This post is the second in a series. Read part one here. p {line-height:1.6em; } p.caption { margin-top:0px;padding-top:0px;margin-bottom:20px;text-align:center;} a.fnote {text-decoration:none;color:red} img {margin-bottom:0px;} “From a mathematics and trajectory standpoint and with a certain kind of technology, there’s not too many different ways to go to Mars. It’s been pretty well figured out. You can adjust the decimal places here and there, but basically if you're talking about chemical rockets, there's a certain way you're going to go to Mars.” - John Aaron[1] Unlike the Moon, which hangs in the sky like a lonely grandparent waiting for someone to visit, Mars leads a rich orbital life of its own and is not always around to entertain the itinerant astronaut. There is just one brief window every 26 months when travel between our two planets is feasible, and this constraint of orbital mechanics is so fundamental that we’ve known since Lindbergh crossed the Atlantic what a mission to Mars must look like.[2] Using chemical rockets, there are just two classes of mission to choose from: (The durations I give here can vary, but are representative). Long Stay: Spend six months flying to Mars, stay for 17 months, spend six months flying back (~1000 days total). This is sometimes called a conjunction class mission. This profile trades a simple out-and-back trajectory for a long stay time at Mars. Short Stay: Spend six months flying to Mars, stay for 30-90 days, spend 400 days flying back (~650 days total). This is also called an opposition class mission. This profile trades a short Martian stay time for a long and frankly terrifying trip home through the inner solar system. Before comparing the merits of each, it’s worth stressing what they have in common—both are long, more than double the absolute record for space flight (438 days), five times longer than anyone has remained in space without resupply (128 days), and about ten times humanity’s accumulated time beyond low Earth orbit (82 days).[3] It is this inconvenient length, more than any technical obstacle, that has kept us from going to Mars since rockets capable of making the trip first became available in the 1960's. [4] And because this length is set by the relative motions of the planets, it’s resistant to attack by technology. You can build rockets that go faster, but unless you make Mars go faster, you’ll mostly end up trading transit time for longer stay times. Getting a round trip below the 500 day mark requires fundamental breakthroughs in either propulsion or refueling. [5] Delta-v requirements for short stay missions of varying length (left) and a long-stay mission (orange line right) for comparison. Note the sharp jump at around 500 days. source. That’s the bad news. The good news is that these constraints are so strong that we can say a lot about going to Mars without committing to any particular spacecraft or mission design. Just like animals that live in the sea are likely to have good hearing and a streamlined body shape, there are things that have to hold true for any Mars-bound spacecraft, just from the nature of the problem. I. No escape, no rescue A trip to Mars will be commital in a way that has no precedent in human space flight. The moon landings were designed so that any moment the crew could hit the red button and return expeditiously to Earth; engineers spent the brief windows of time when an abort was infeasible chain smoking and chewing on their slide rules. [6] But within a few days of launch, a Mars-bound crew will have committed to spending years in space with no hope of resupply or rescue. If something goes wrong, the only alternative to completing the mission will be to divert into a long, looping orbit that gets the spacecraft home about two years after departure.[7] And if they get stuck on Mars, astronauts will find themselves in a similar position to the early Antarctic explorers, able to communicate home by radio, but forced by unalterable cycles of nature to wait months or years for a rescue ship. Delta-v in km/sec required to return to Earth in 50, 70, and 90 days from various points in a long-stay Mars mission. Values above 10 km/sec are not realistic at our current technology level. source The effect of this no-abort condition is to make Mars mission design acutely risk-averse. You can think of flying to Mars like one of those art films where the director has to shoot the movie in a single take. Even if no scene is especially challenging, the requirement that everything go right sequentially, with no way to pause or reshoot, means that even small risks become unacceptable in the aggregate. To get a feel for this effect, consider a toy model where we fly to Mars on a 30 month mission. Every month there is a 3% chance that a critical system on our spacecraft will fail, and once that happens, the spacecraft enters a degraded state, with a 5% chance every month that a subsequent failure kills the crew. In this model, the probability that the crew gets home safely works out to 68%. But if we add an abort option that can get them home in six months, that probability jumps to 85%. And with a three month abort trajectory, the odds of safe return go up to 92%. These odds are notional, but they demonstrate how big an effect the absence of abort options can have on safety.[8] This necessary risk aversion introduces a tension into any Mars program. What’s the point of spending a trillion dollars to send a crew if they’re going to cower inside their spacecraft? And yet since going outside is one of the most dangerous things you can do on Mars, early missions have to minimize it. The first visitors to Mars will have to land in the safest possible location and do almost nothing. Risk is closely tied with the next issue, reliability. II. Reliability The closest thing humanity has built to a Mars-bound spacecraft is the International Space Station. But ‘reliable’ is not the first word that leaps to the lips of ISS engineers when they talk about their creation—not even the first printable word. Despite twenty years of effort, equipment on the station breaks constantly, and depends on a stream of replacement parts flown up from Earth.[9] A defective heat exchanger packaged for return to Earth from ISS in 2023 Going to Mars will require order of magnitude reliability improvements over the status quo. Systems on the spacecraft will need to work without breaking, or at least break in ways the crew can fix. If there’s an emergency, like a chemical leak or a fire, the crew must be able to live for years in whatever’s left of the ship. And the kind of glitches that made for funny stories in low Earth orbit (like a urine icicle blocking the Space Shuttle toilet) will be enough to kill a Mars-bound crew. Complicating matters is that traditional reliability engineering practices don’t work in life support, where everything is interconnected, often through the bodies of the crew. Life support engineering is much more like keeping a marine aquarium than it is like building a rocket. It’s not easy to untangle cause from effect, the entire system evolves over time, and there’s a lot of “spooky action at a distance” between subsystems that were supposed to be unrelated.[10] Indeed, failures in life support have a tendency to wander the spacecraft until they find the most irreplaceable thing to break. Nor is it possible to brute-force things by filling the spacecraft with spare parts. The same systemic interactions that damage one component can eat through any number of replacements. The bedrock axiom of reliability engineering—that complex designs can be partitioned into isolated subsystems with independent failure rates—does not hold for regenerative life support. The need for long and expensive test flights to validate life support introduces another kind of risk aversion, this time in the design phase. With prototypes needing to be flown for years in space, there will be pressure to freeze the life support design at whatever point it becomes barely adequate, and no amount of later innovation will make it onto the spacecraft. This is a similar dynamic to one that afflicted the Space Shuttle, a groundbreaking initial design so expensive to modify that it froze the underlying technology at the prototype phase for thirty years. In that period we learned nothing about making better space planes, but burned through decades and billions of dollars patching up the first working prototype. Such timorousness goes against the grain of a development strategy that proven spectacularly successful in recent years for SpaceX, an approach you could call “fly often and try everything”. With hardware to spare, SpaceX is not afraid to make wholesale changes between tests of its Starship rocket, relying on rapid iterations to advance the state of the art at an exhilarating pace. But this Yosemite Sam approach to testing won’t work for Mars. It only takes a few hours for engineers to collect the data they need after a Starship launch, while test runs of Mars-bound systems will last for years. The inevitable outcome is a development program that looks an awful lot like NASA, with long periods of fussing and analysis punctuated by infrequent, hideously expensive test flights. III. Autonomy Autonomy is a concept alien to NASA, which has been micromanaging astronauts from the ground since the first Mercury astronaut had to beg controllers for permission to pee (the request went all the way up the reporting chain to Wernher Von Braun). To this day, missions follow a test pilot paradigm where the crew works from detailed checklists prepared for them months or years in advance. On the space station, this takes the form of a graphical schedule creeping past a red vertical line on a laptop screen, with astronauts expected to keep pace with the moving colored boxes. Most routine work on the space station (like pumping water or managing waste heat) is relegated to specialized teams on the ground and is not even visible to the crew. Alan Shepard aboard Freedom 7, explaining that he really has to go pretty bad. But as a Mars-bound spacecraft gets further from Earth, the round-trip communications delay with ground control will build to a maximum of 43 minutes, culminating in a week or more of communications blackout when the Sun is directly between the two planets. This physical constraint means that the crew has to have full control over every system on the spacecraft, without help from the ground. Autonomy sounds like a good thing! Who wants government bean-counters deciding how astronauts spend their space time? But the ground-driven paradigm has its advantages, most notably in limiting workload. The ISS is run by a staff of hundreds who together send some 50,000 commands per day to the station. The seven astronauts on board are only called in as a last resort, and even so the demands on their time are so great that the station has struggled to perform its scientific mission.[11] One benefit of NASA’s backseat driving has always been that in an emergency, the crew has access to unlimited real-time expert help on Earth. The starkest illustration of this came on Apollo 13, when an oxygen tank in the service module ruptured 56 hours into the flight. It took the crew and mission controllers nearly an hour to get their bearings, at which point there was only a short window of time left to power down the spacecraft in a way that would preserve their ability to return to Earth. A transcript of that first hour shows how difficult it was for crew and ground to figure out what was happening, and prioritize their response. It casts no aspersions on the crew of Apollo 13 to say they could not have survived a Mars-like communications delay. And while this mission is the most famous example of ground controllers backstopping an Apollo crew, there were at least five more occasions in the Apollo program when timely help from the ground averted serious trouble: Apollo 12 was hit twice by lightning after launch, scrambling the electrical system and lighting up the command module with warning lights. Flight controller John Aaron recognized the baffling error pattern and passed into NASA legend by telling the crew to flip an obscure switch that restored sanity to their displays. On Apollo 14, the descent radar on the lunar module failed to lock on properly, returning spurious range data. Without a timely call from ground control (who told the pilot to reset a breaker), the problem would likely have led to an aborted landing. On Apollo 15, the crew struggled to contain a water leak that threatened to become serious. After fifteen minutes, engineers on the ground were able to trace the problem to a pre-launch incident with a chlorination valve and relay up a procedure that solved the problem. Also on Apollo 15, a sliver of loose metal floating in a switch caused an intermittent abort signal to be sent to the lunar module engine. Suppressing the signal so the lunar module could descend safely required reprogramming the onboard computer in a procedure guaranteed to raise the hairs on the head of every modern software developer. On Apollo 16, a pair of servo motors on the service module failed in lunar orbit. Mission rules called for an abort, but after some interactive debugging with the command module pilot, ground controllers found a workaround they judged safe enough to continue with the landing. While these incidents stand out, Apollo transcripts reveal numberless other examples of crew and ground working closely to get on top of problems. The loss of this real-time help is a real risk magnifier for astronauts going to Mars. IV. Analysis Another way in which the ISS depends on Earth is for laboratory analysis of air and water samples, which are collected on a regular schedule and sent down with each returning capsule. The tests that can be performed on the station itself are rudimentary, alerting crew to the presence of microbes or contaminants, but without the detailed information necessary to trace a root cause. For Mars, this analytic capability will have to move into the spacecraft. In essence, this means building a kind of Space Theranos, an automated black box that can perform biochemical assays in space without requiring repair or calibration. Such an instrument doesn’t exist anywhere, but a Mars mission requires two flavors of it—one that works in zero G, and another for Martian gravity.[12] This black box belongs to a category of hardware that pops up a lot in Mars plans: technologies that would be multibillion dollar industries if they existed on Earth, but are assumed to be easy enough to invent when the time comes to put them on a Mars-bound spacecraft. [13] Some Mars boosters even cite these technologies as examples of the benefits going to Mars will bring to humanity. But this gets things exactly backwards—problems that are hard on Earth don’t get easier by firing them into space, and the fact that nonexistent technologies are on the critical path to Mars is not an argument for going there. V. Automation The requirement that the crew be able to handle the ship when some members are incapacitated and there is no communication with Earth means that an ISS-size workload has to be automated to the point where it can be run by two or three astronauts. Astronaut Alexander Gerst (right) interacting with CIMON, NASA's $6 million AI chatbot Automation means software, and lots of it. To automate the systems on a Mars-bound spacecraft will be a monumental task, like trying to extend the autopilot on an airliner to make it run the airport concession stands, baggage claim, and airline pension plan. The likely outcome is an ISS-like hotchpotch of software tested to different levels of rigor, running across hundreds of processors. But this hardware will be exposed to a far harsher radiation environment than systems on the ISS, making software design and integration a particular challenge. A special case of the automation problem comes up on long-stay missions, when the orbiting spacecraft has to keep itself free of mold, fungus, and space raccoons for the year and a half that the crew are on the Martian surface. Anyone who owns a vacation home knows that this problem—called “quiescence” in the Mars literature—is already hard to solve on Earth. Unless carefully managed, the interplay between automation, complexity and reliability can enter a pathological spiral. Adding software to a system makes it more complex. To stay reliable, complex systems have to degrade gracefully, so that the whole continues to function even if an individual component fails. But these degraded modes, as well as unexpected interactions between them, introduce their own complexity, which then has to be managed with software, and so on. The upshot is that automation introduces its own, separate reason for running full-length mock missions before actually going to Mars. There will be too many bugs in a system this complex to leave them all for the first Mars-bound crew to discover. Implications The extreme requirements for autonomy, reliability, and automation I’ve outlined are old news to designers of deep-space probes. The solar system is full of hardware beeping serenely away decades after launch, most spectacularly the forty-six-year-old Voyager spacecraft. But no one has ever tried attaching a box of large primates to a deep space probe with the goal of keeping them alive, happy, and not tweeting about how NASA sent them into the vast empty spaces to die. A Mars-bound spacecraft will be the most complicated human artifact ever built, about a hundred times bigger than any previous space probe, and inside it will be a tightly-coupled system of software, hardware, bacteria, fungi, astronauts, and (for half the mission) whatever stuff the crew tracks with them back onto the spacecraft. Designing such a machine means taking something at the ragged edge of human ability (building interplanetary probes) and combining it with something that we can’t even do yet on Earth (keep a group of six or eight humans alive for years with regenerative life support).[14] My argument is not that it is impossible to do this, but that it is impossible to do it quickly. Preparing for Mars will be an iterative, open-ended undertaking in which every round of testing eats up years of time and most of our space budget, like Artemis and the ISS before it. The first decade of a Mars program will be indistinguishable from the last forty years of space flight—a series of repetitive, long-duration missions to orbit. The only thing NASA will need to change is the program name. Nor is this a problem that can be delegated to billionaire hobbyists. Life support is going to be a grind no matter whose logo is on the rocket. The sky could be thick with Starships and we’d still be stuck doing all-up trials of hardware and software on these multi-year missions to nowhere. The only way to explore Mars in our lifetime is to ditch the requirement that people accompany the machinery. Choosing a profile But since we’re determined to go to Mars, and have two profiles to choose from, which one is better? Everyone agrees that only the long-stay profile makes sense for exploration. There’s no point in spending 95% of the trip in transit just to get a rushed couple of weeks at the destination. But on early missions, where the goal is just to get the crew home alive, the choice is tricky. Long Stay The virtue of the long stay profile is simplicity. You fly your rocket to Mars, wait 17 months for the planets to align, and then fly the same trajectory home. Each leg of this transfer journey lasts about as long as an ISS deployment, and it’s possible to tweak the transfer time by burning more fuel (although the crew then has to stay longer on Mars to compensate). At every point in the mission, the ship remains between 1 AU and 1.5 AU from the Sun. This simplifies thermal and solar panel design and greatly reduces the risk to the crew from solar storms. But the problem of what to do with all that time on Mars is vexing. 500 days is a long time for a first stay anywhere, even someplace with nightlife and an atmosphere. And as we’ll see, an orbital mission is probably out of the question. The requirement that the crew go live on Mars on their first visit adds enormously to the level of risk. Short Stay The appeal of the short stay profile is right in the name. Instead of staying on Mars so long they have to file taxes, the first arrivals can plant the flag, grab whatever rock is nearest the ladder, and get the hell out of there. Or they can choose to skip the landing and make the first trip strictly orbital, following a tradition in aerospace engineering of attempting the impossible sequentially instead of all at once. But the problem with the short stay profile is that trip home. The return trajectory cuts well inside the orbit of Venus, complicating the design of the spacecraft and adding spectacular ways for the crew to die during the weeks near perihelion. For most of that journey, the ship is on the wrong side of the Sun, hampering communications with Earth while leaving the crew with no warning of solar storms. And that crew has to spend two consecutive years in deep space, maximizing their exposure to radiation and microgravity, the biggest known risks to astronaut health. The short stay profile also requires more propellant, in some years a prohibitive amount. If your strategy for mitigating risk on Mars is to launch crews during every synodic period, so that there are always potential rescuers en route to Mars, then this is a problem.  A diagram comparing the delta-v requirements for short stay and long stay missions across future launch dates. Since propellant requirements go up exponentially with delta v, a mission in 2041 requires five times as much propellant as one in 2033. source“ Orbit or Land? Once you’ve picked a profile, the other decision to make is whether to land the spacecraft. Obviously you have to land a crew at some point; if you don’t, the other space programs will make fun of you, and there will be hurtful zingers at your Congressional hearing. But since surviving a trip to Mars requires tackling a sequence of unrelated problems (arrival, entry, landing, surface operations, ascent, rendezvous), there is a case for cutting the problem in half by making the first mission orbital. This was the approach taken by the Apollo program, which looped the first crew around the Moon before a working lunar lander existed. Not having to carry a lander on the first mission means more room for spare parts and consumables, which improves the margin of safety for the crew. It also buys time for engineers to work on the hard problems of entry, landing, quiescence, and ascent without holding back the entire program. But there are powerful arguments against an orbital mission. Since so much of the risk in going to Mars is a simple function of time, why roll the dice more than necessary? And given the expense and physical toll on crew, how do you justify not attempting a landing? Imagine driving to Disneyland, turning the car around in the parking lot, and announcing to your family that you’re now ready for the real trip next year. There will be angry kicking from the backseat, and mutiny. NASA has waffled for years over which option to choose. In the 2009 design reference architecture, they favored sending a crew of four on the long stay trajectory. Their more recent plans envision a shoestring mission on a short-stay profile with four crew members, two of whom attempt a landing. Elon Musk, for his part, has proposed solving the problem in stages, sending volunteers to settle Mars first, then figuring out how to get them home later.[15] What makes the choice genuinely hard is that we lack answers to two key questions: 1. How does the human body respond to partial gravity? Decades in space have given us a good idea of what prolonged periods in free-fall do to astronauts, and how they recover after returning to Earth. But we have no idea what happens in partial gravity, either on the Moon (0.16 g) or on Mars (0.38 g). In particular, we don’t know whether Martian gravity is strong enough to arrest or slow the degenerative processes that we observe in free fall.[16] The answer to this question will drive a key decision: whether or not to spin the spacecraft. As we’ll see, spinning a spacecraft to create artificial gravity is an enormous hassle, but whether it’s avoidable depends on the unstudied effects of long stays in partial gravity.[17] 2. What is the risk to the crew from the heavy-ion component of galactic cosmic radiation? Radiation in space comes in many varieties, most of which are well-understood from experience with their analogues on Earth. Low-dose heavy-ion radiation, however, is different. It doesn’t exist outside of particle accelerators on Earth and is hard to study in low orbit, where both the magnetosphere and the bulk of our planet shield astronauts from most of the flux they’d experience in free space. Heavy ion radiation has biological effects that are not captured by the standard model of radiation damage to tissue. In particular, there is a class of phenomena called non-targeted effects (NTEs) that are known to damage cells far from the radiation track. This is a weird effect, like if found yourself hospitalized because your neighbor got hit by a car. It’s believed that NTEs disrupt epigenetic signaling mechanisms in cells, but the phenomenon is poorly understood. Uncertainty about the effects of low-dose heavy ion radiation widens our best guess at radiation risk by at least a factor of two.[18] At the low end of the range, these effects are just a curiosity, and Mars missions can be planned using traditional models of radiation exposure. At the high end of the range, long-duration orbital missions may not be survivable, and astronauts on the Martian surface will either have to live in a cave or cover their shelter with meters of soil. Prediction of tumor prevalence after 1 year of galactic cosmic radiation exposure. The solid line at bottom shows the standard radiation model (TE). The dotted lines show the influence of non-targeted effects (NTE) under different assumptions. Note the nearly threefold uncertainty in predicted tumor prevalence in the unshielded case. source This uncertainty about biological effects makes radiation the greatest uncharacterized known risk facing a Mars-bound crew, and it affects every aspect of mission design. It’s helpful to combine the three main risk factors in going to Mars into one big chart:  table.risk { font-size:1.1em; margin:0px; margin-top:20px; width:550px; border-spacing:0px; } caption { font-size:1.2em; margin-bottom:10px; color:#777; } th { text-align:center; padding-bottom:10px; } td { text-align:left; padding:14px; margin:0px; } td.risk {border:1px solid #777;} td.unknown { background:#888; color:white; } td.low { background:#afa; } td.mid { background:#ff9; } td.high { background:#fc9; } td.vhigh { background:#f99; } Technical Risk OrbitLand Short Stay Spacecraft trajectory complicates spacecraft design, communications are a challenge. Requires working lander and ascent stage, less margin than orbital mission. Long Stay Lowest complexity, large mass budget for spares and consumables. Highest complexity, all-up mission must work on the first try. Radiation Risk OrbitLand Short Stay 600 days in deep space, return trip requires close solar approach (0.7 AU). Risk from solar particle events may require flying near solar minimum, incurring higher GCR dose. Long Stay Risk of death or incapacitation from heavy ion component of GCR may exceed 50% Lowest radiation exposure, but adequately shielding the habitat on Mars increases complexity and contamination risk Deconditioning Risk OrbitLand Short Stay 1.5 times beyond human endurance record; crew at risk for bone fractures and eye damage. Long Stay 2.5 times beyond human endurance record. Physiological effects of partial gravity unknown. The gray areas in these grids represent knowledge gaps that have to be filled before we decide how to go to Mars. How long this preliminary medical research would take is anyone’s guess, but it has to be some multiple of the total mission time. Studying partial gravity in particular is tricky—you can do it on the Moon (42% of martian gravity) and hope the results extend to Mars, or you can build rotating structures in space and do more precise tests there. Studying radiation effects means flying animals outside the magnetosphere for a few years and then watching them for tumors, which (unless the radiation news is really bad) is also going to take some time. In software engineering we have a useful concept called “yak shaving”. To get started on a project you must first prepare your tools, which often involves reconfiguring your programming environment, which may mean updating software, which requires finding a long-disused password, and pretty soon you find yourself under the office chair with a hex wrench. (The TV show Malcolm in the Middle has a beautiful illustration of yak shaving in the context of home repair.) The same phenomenon afflicts us in trying to go to Mars. It would be one thing if, given enough rockets and money, explorers could climb on a spaceship and go. But there is always this chain of necessary prerequisites. We paint Destination: Mars! on the side of our spaceship and then find ourselves in low Earth orbit a decade later, centrifuging mice. It’s dispiriting. It’s tempting to say “you can just build things” and dismiss all this research and testing as timid and unnecessary. But this would mean ignoring the biggest risk factor for Mars, which I’ll include here for the sake of completeness. Unknown Risks OrbitLand Short Stay Unknown Unknown Long Stay Unknown Unknown A trip to Mars is so difficult that we don’t have the luxury of ignoring known risks—we need all the room we can spare in our risk budget for the things we don’t know to worry about yet. My goal in all this is not to kill a cherished dream, but to try to push people to a more realistic view of what it means to commit to a Mars landing, and in particular to think about going to Mars in terms of opportunity costs. In recent years, there’s been a remarkable division in space exploration. On one side of the divide are missions like Curiosity, James Webb, Gaia, or Euclid that are making new discoveries by the day. These projects have clearly defined goals and a formidable record of discovery. On the other side, there is the International Space Station and the now twenty-year old effort to return Americans to the moon. These projects have no purpose other than perpetuating a human presence in space, and they eat through half the country’s space budget with nothing to show for it. Forget even Mars—we are further from landing on the Moon today than we were in 1965. In going to Mars, we have a choice about which side of this ledger to be on. We can go aggressively explore the planet with robots, benefiting from an ongoing revolution in automation and software to launch ever more capable missions to the places most likely to harbor life. Or we can stay on the treadmill we’ve been on for forty years, slowly building up the capacity to land human beings on the safest possible piece of Martian real estate, where they will leave behind a plaque and a flag. But we can’t do both. Next time: Eyes and Bones Footnotes [1] Quote taken from a 2000 oral history with Aaron. [2] For an early example, see the 1928 Scientific American article, “Can we go to Mars?”, While understandably hand-wavy about the means of propulsion, it describes a conjunction-class orbital mission not substantially different from NASA’s 2009 Design Reference Architecture. [3] Valerii Polyakov set the 437 day record on a space flight that landed in 1995. The International Space Station went without resupply from Nov 25, 2002 to April 2, 2003. Nine Apollo missions went beyond low Earth orbit, the longest of these (Apollo 17) was gone 12.4 days. [4] The Saturn V was capable of launching about 20 tons on a Mars flyby trajectory. NASA undertook preliminary planning for such a mission (requiring four Saturn V launches) in 1967. [5] In 1987 a team chaired by Sally Ride proposed a ‘split/sprint’ mission architecture that is probably the best way to get to Mars. In this architecture, slow-moving tankers pre-position cryogenic propellant depots in Mars orbit, and then in the next synodic period a human mission (the “sprint” part of the mission) lands briefly on Mars, refuels from the orbiting depots, and get home within 400 days. Such a mission requires about 15 heavy launches and two nonexistent technologies: long-term storage of liquid hydrogen in space, and the ability to pump liquid hydrogen between spacecraft in space. (Interestingly, both of these technologies are part of Blue Origin's plan to build a moon lander). The other way to get to Mars fast is with nuclear thermal rockets. A nuclear thermal rocket is just a nuclear reactor that shoots hot hydrogen out one end. Nuclear thermal rocket designs are about twice as efficient as chemical rockets, making it feasible to fly missions with higher delta V requirements. [6] For a comprehensive discussion of Apollo abort modes, see 1972 Apollo Experience Report - Abort Planning. [7] You can read about possible Mars abort modes in Earth to mars Abort Analysis for Human Mars Missions. What kind of a failure scenario would even benefit from a two-year abort option is an interesting philosophical question. [8] I wrote a little python script if you want to play with these scenarios yourself. [9] Life support equipment on ISS is packaged into components called ‘Orbital Replacement Units’. In some cases, this means that an assembly weighing hundreds of kilograms has to be flown up because a tiny sensor within it failed. Here's a partial list of ORUs replaced in calendar year 2023 (source): Heat exchanger in Node 3 Common cabin air assembly water separator Node 3 water separator Common cabin air assembly water separator liquid check valve 21 charcoal filters stationwide HEPA filters in Node 3 Blower in carbon dioxide removal assembly (twice, first replacement failed) Sample Distribution Assembly in Node 3 Mass Spectrometer assembly Multifiltration bed Pump in oxygen generation assembly [10] An early urine reprocessor on the space station failed after it got clogged up by calcium crystals from the astronauts' dissolving bones, an effect of weightlessness that wasn't properly accounted for in the design. [11] The 50,000 command figure is from The ISS: Operating an Outpost in the New Frontier, a detailed primer on space station operations. ISS utilization has gone up in recent years, but still remains below 80 hours/week—two full-time equivalents. The seven-member crew spends most of their waking time on mandatory exercise, housekeeping, and station repair. [12] Existing instruments in space are usually set up to identify chemicals on a target list of 10-20 substances, a much easier task than identifying arbitrary compounds. For the state of the art on the latter, see Progress on the Organic and Inorganic Modules of the Spacecraft Water Impurity Monitor, a Next Generation Complete Water Analysis System for Crewed Vehicles (ICES-2023-110). [13] Other examples of magic Mars technology include leakless seals for spacesuits, waterless washing machines, biofilm-proof coatings, nutritionally complete meals that can be stored for years at room temperature, and autonomous solar-powered factories for turning CO2 into hundreds of tons of methane. [14] The endurance record for closed-system life support belongs to Biosphere 2, which kept a crew alive for 17 months before oxygen fell to dangerous levels because of unanticipated interactions with building materials. [15] Plans involving Starship and Mars depend on being able to produce hundreds of tons of propellant on the Martian surface so the rockets can launch again. In the absence of any details from Musk or SpaceX, the closest thing we have to a detailed plan is this analysis in Nature. [16] For all we know, the set of problems collectively called "deconditioning" could get worse in partial gravity. This goes against our intuitions, but there have been bigger surprises in space. [17] Another decision that hinges on the effects of partial gravity is whether or not to include heavy exercise equipment on the Mars surface habitat, where space and mass are at a premium.

Introduction A Note on Apollo I. The Rocket II. The Capsule III. The Orbit IV. Gateway V. The Lander VI. Refueling VII. Conclusion Notes A little over 51 years ago, a rocket lifted off from Cape Canaveral carrying three astronauts and a space car. After a three day journey to the moon, two of the astronauts climbed into a spindly lander and made the short trip down to the surface, where for another three days they collected rocks and did donuts in the space car. Then they climbed back into the lander, rejoined their colleague in orbit, and departed for Earth. Their capsule splashed down in the South Pacific on December 19, 1972. This mission, Apollo 17, would be the last time human beings ventured beyond low Earth orbit. If you believe NASA, late in 2026 Americans will walk on the moon again. That proposed mission is called Artemis 3, and its lunar segment looks a lot like Apollo 17 without the space car. Two astronauts will land on the moon, collect rocks, take selfies, and about a week after landing rejoin their orbiting colleagues to go back to Earth. But where Apollo 17 launched on a single rocket and cost $3.3 billion (in 2023 dollars), the first Artemis landing involves a dozen or two heavy rocket launches and costs so much that NASA refuses to give a figure (one veteran of NASA budgeting estimates it at $7-10 billion).[1] The single-use lander for the mission will be the heaviest spacecraft ever flown, and yet the mission's scientific return—a small box of rocks—is less than what came home on Apollo 17. And the whole plan hinges on technologies that haven't been invented yet becoming reliable and practical within the next eighteen months. You don’t have to be a rocket scientist to wonder what’s going on here. If we can put a man on the moon, then why can't we just go do it again? The moon hasn’t changed since the 1960’s, while every technology we used to get there has seen staggering advances. It took NASA eight years to go from nothing to a moon landing at the dawn of the Space Age. But today, twenty years and $93 billion after the space agency announced our return to the moon, the goal seems as far out of reach as ever.[2] Articles about Artemis often give the program’s tangled backstory. But I want to talk about Artemis as a technical design, because there’s just so much to drink in. While NASA is no stranger to complex mission architectures, Artemis goes beyond complex to the just plain incoherent. None of the puzzle pieces seem to come from the same box. Half the program requires breakthrough technologies that make the other half unnecessary. The rocket and spacecraft NASA spent two decades building can’t even reach the moon. And for reasons no one understands, there’s a new space station in the mix. In the past, whatever oddball project NASA came up with, we at least knew they could build the hardware. But Artemis calls the agency’s competence as an engineering organization into question. For the first time since the early 1960's, it's unclear whether the US space agency is even capable of putting astronauts on the moon. A Note on Apollo In this essay I make a lot of comparisons to Project Apollo. This is not because I think other mission architectures are inferior, but because the early success of that program sets such a useful baseline. At the dawn of the Space Age, using rudimentary technology, American astronauts landed on the moon six times in seven attempts. The moon landings were NASA’s greatest achievement and should set a floor for what a modern mission, flying modern hardware, might achieve. Advocates for Artemis insist that the program is more than Apollo 2.0. But as we’ll see, Artemis can't even measure up to Apollo 1.0. It costs more, does less, flies less frequently, and exposes crews to risks that the steely-eyed missile men of the Apollo era found unacceptable. It's as if Ford in 2024 released a new model car that was slower, more accident-prone, and ten times more expensive than the Model T. When a next-generation lunar program can’t meet the cost, performance, or safety standards set three generations earlier, something has gone seriously awry. I. The Rocket The jewel of Artemis is a big orange rocket with a flavorless name, the Space Launch System (SLS). SLS looks like someone started building a Space Shuttle and ran out of legos for the orbiter. There is the familiar orange tank, a big white pair of solid rocket boosters, but then the rocket just peters out in a 1960’s style stack of cones and cylinders. The best way to think of SLS is as a balding guy with a mullet: there are fireworks down below that are meant to distract you from a sad situation up top. In the case of the rocket, those fireworks are a first stage with more thrust than the Saturn V, enough thrust that the boosted core stage can nearly put itself into orbit. But on top of this monster sits a second stage so anemic that even its name (the Interim Cryogenic Propulsion Stage) is a kind of apology. For eight minutes SLS roars into the sky on a pillar of fire. And then, like a cork popping out of a bottle, the tiny ICPS emerges and drifts vaguely moonwards on a wisp of flame. With this design, the minds behind SLS achieved a first in space flight, creating a rocket that is at the same time more powerful and less capable than the Saturn V. While the 1960’s giant could send 49 metric tons to the moon, SLS only manages 27 tons—not enough to fly an Apollo-style landing, not enough to even put a crew in orbit around the moon without a lander. The best SLS can do is slingshot the Orion spacecraft once around the moon and back, a mission that will fly under the name Artemis 2. NASA wants to replace ICPS with an ‘Exploration Upper Stage’ (the project has been held up, among other things, by a near-billion dollar cost overrun on a launch pad). But even that upgrade won’t give SLS the power of the Saturn V. For whatever reason, NASA designed its first heavy launcher in forty years to be unable to fly the simple, proven architecture of the Apollo missions. Of course, plenty of rockets go on to enjoy rewarding, productive careers without being as powerful as the Saturn V. And if SLS rockets were piling up at the Michoud Assembly Facility like cordwood, or if NASA were willing to let its astronauts fly commercial, it would be a simple matter to split Artemis missions across multiple launches. But NASA insists that astronauts fly SLS. And SLS is a “one and done” rocket, artisanally hand-crafted by a workforce that likes to get home before traffic gets bad. The rocket can only launch once every two years at a cost of about four billion dollars[3]—about twice what it would cost to light the rocket’s weight in dollar bills on fire[4]. Early on, SLS designers made the catastrophic decision to reuse Shuttle hardware, which is like using Fabergé eggs to save money on an omelette. The SLS core stage recycles Space Shuttle main engines, actual veterans of old Shuttle flights called out of retirement for one last job. Refurbishing a single such engine to work on SLS costs NASA $40 million, or a bit more than SpaceX spends on all 33 engines on its Superheavy booster.[5] And though the Shuttle engines are designed to be fully reusable (the main reason they're so expensive), every SLS launch throws four of them away. Once all the junkyards are picked clean, NASA will pay Aerojet Rocketdyne to restart production of the classic engine at a cool unit cost of $145 million[6]. The story is no better with the solid rocket boosters, the other piece of Shuttle hardware SLS reuses. Originally a stopgap measure introduced to save the Shuttle budget, these heavy rockets now attach themselves like barnacles to every new NASA launcher design. To no one’s surprise, retrofitting a bunch of heavy steel casings left over from Shuttle days has saved the program nothing. Each SLS booster is now projected to cost $266 million, or about twice the launch cost of a Falcon Heavy.[7] Just replacing the asbestos lining in the boosters with a greener material, a project budgeted at $4.4M, has now cost NASA a quarter of a billion dollars. And once the leftover segments run out seven rockets from now, SLS will need a brand new booster design, opening up fertile new vistas of overspending. Costs on SLS have reached the point where private industry is now able to develop, test, and launch an entire rocket program for less than NASA spends on a single engine[8]. Flying SLS is like owning a classic car—everything is hand built, the components cost a fortune, and when you finally get the thing out of the shop, you find yourself constantly overtaken by younger rivals. But the cost of SLS to NASA goes beyond money. The agency has committed to an antiquated frankenrocket just as the space industry is entering a period of unprecedented innovation. While other space programs get to romp and play with technologies like reusable stages and exotic alloys, NASA is stuck for years wasting a massive, skilled workforce on a dead-end design. The SLS program's slow pace also affects safety. Back in the Shuttle era, NASA managers argued that it took three to four launches a year to keep workers proficient enough to build and launch the vehicles safely. A boutique approach where workers hand-craft one rocket every two years means having to re-learn processes and procedures with every launch. It also leaves no room in Artemis for test flights. The program simply assumes success, flying all its important 'firsts' with astronauts on board. When there are unanticipated failures, like the extensive heat shield spalling and near burn-through observed in Artemis 1,[9] the agency has no way to test a proposed fix without a multi-year delay to the program. So they end up using indirect means to convince themselves that a new design is safe to fly, a process ripe for error and self-delusion. II. The Capsule Orion, the capsule that launches on top of SLS, is a relaxed-fit reimagining of the Apollo command module suitable for today’s larger astronaut. It boasts modern computers, half again as much volume as the 1960’s design, and a few creature comforts (like not having to poop in a baggie) that would have pleased the Apollo pioneers. The capsule’s official name is the Orion Multipurpose Crew Vehicle, but finding even a single purpose for Orion has greatly challenged NASA. For twenty years the spacecraft has mostly sat on the ground, chewing through a $1.2 billion annual budget. In 2014, the first Orion flew a brief test flight. Eight short years later, Orion launched again, carrying a crew of instrumented mannequins around the moon on Artemis 1. In 2025 the capsule (by then old enough to drink) is supposed to fly human passengers on Artemis 2. Orion goes to space attached to a basket of amenities called the European Service Module. The ESM provides Orion with solar panels, breathing gas, batteries, and a small rocket that is the capsule’s principal means of propulsion. But because the ESM was never designed to go to the moon, it carries very little propellant—far too little to get the hefty capsule in and out of lunar orbit.[10] And Orion is hefty. Originally designed to hold six astronauts, the capsule was never resized when the crew requirement shrank to four. Like an empty nester’s minivan, Orion now hauls around a bunch of mass and volume that it doesn’t need. Even with all the savings that come from replacing Apollo-era avionics, the capsule weighs almost twice as much as the Apollo Command Module. This extra mass has knock-on effects across the entire Artemis design. Since a large capsule needs a large abort rocket, SLS has to haul Orion's massive Launch Abort System—seven tons of dead weight—nearly all the way into orbit. And reinforcing the capsule so that abort system won't shake the astronauts into jelly means making it heavier, which puts more demand on the parachutes and heat shield, and around and around we go. Size comparison of the Apollo command and service module (left) and Orion + European Service Module (right) What’s particularly frustrating is that Orion and ESM together have nearly the same mass as the Apollo command and service modules, which had no trouble reaching the moon. The difference is all in the proportions. Where Apollo was built like a roadster, with a small crew compartment bolted onto an oversized engine, Orion is the Dodge Journey of spacecraft—a chunky, underpowered six-seater that advertises to the world that you're terrible at managing money. III. The Orbit The fact that neither its rocket or spaceship can get to the moon creates difficulties for NASA’s lunar program. So, like an aging crooner transposing old hits into an easier key, the agency has worked to find a ‘lunar-adjacent’ destination that its hardware can get to. Their solution is a bit of celestial arcana called Near Rectilinear Halo Orbit, or NRHO. A spacecraft in this orbit circles the moon every 6.5 days, passing 1,000 kilometers above the lunar north pole at closest approach, then drifting out about 70,000 kilometers (a fifth of the Earth/Moon distance) at its furthest point. Getting to NRHO from Earth requires significantly less energy than entering a useful lunar orbit, putting it just within reach for SLS and Orion.[11] To hear NASA tell it, NRHO is so full of advantages that it’s a wonder we stay on Earth. Spacecraft in the orbit always have a sightline to Earth and never pass through its shadow. The orbit is relatively stable, so a spacecraft can loiter there for months using only ion thrusters. And the deep space environment is the perfect place to practice going to Mars. But NRHO is terrible for getting to the moon. The orbit is like one of those European budget airports that leaves you out in a field somewhere, requiring an expensive taxi. In Artemis, this taxi takes the form of a whole other spaceship—the lunar lander—which launches without a crew a month or two before Orion and is supposed to be waiting in NRHO when the capsule arrives. Once these two spacecraft dock together, two astronauts climb into the lander from Orion and begin a day-long descent to the lunar surface. The other two astronauts wait for them in NRHO, playing hearts and quietly absorbing radiation. Apollo landings also divided the crew between lander and orbiter. But those missions kept the command module in a low lunar orbit that brought it over the landing site every two hours. This proximity between orbiter and lander had enormous implications for safety. At any point in the surface mission, the astronauts on the moon could climb into the ascent rocket, hit the big red button, and be back sipping Tang with the command module pilot by bedtime. The short orbital period also gave the combined crew a dozen opportunities a day to return directly to Earth. [12] Sitting in NRHO makes abort scenarios much harder. Depending on when in the mission it happens, a stricken lander might need three or more days to catch up with the orbiting Orion. In the worst case, the crew might find themselves stuck on the lunar surface for hours after an abort is called, forced to wait for Orion to reach a more favorable point in its orbit. And once everyone is back on Orion, more days might pass before the crew can depart for Earth. These long and variable abort times significantly increase risk to the crew, making many scenarios that were survivable on Apollo (like Apollo 13!) lethal on Artemis. [13] The abort issue is just one example of NRHO making missions slower. NASA likes to boast that Orion can stay in space far longer than Apollo, but this is like bragging that you’re in the best shape of your life after the bank repossessed your car. It's an oddly positive spin to put on bad life choices. The reason Orion needs all that endurance is because transit times from Earth to NRHO are long, and the crew has to waste additional time in NRHO waiting for orbits to line up. The Artemis 3 mission, for example, will spend 24 days in transit, compared to just 6 days on Apollo 11. NRHO even dictates how long astronauts stay on the moon—surface time has to be a multiple of the 6.5 day orbital period. This lack of flexibility means that even early flag-and-footprints missions like Artemis 3 have to spend at least a week on the moon, a constraint that adds considerable risk to the initial landing. [14] In spaceflight, brevity is safety. There's no better way to protect astronauts from the risks of solar storms, mechanical failure, and other mishaps than by minimizing slack time in space. Moreover, a safe architecture should allow for a rapid return to Earth at any point in the mission. There’s no question astronauts on the first Artemis missions would be better off with Orion in low lunar orbit. The decision to stage from NRHO is an excellent example of NASA designing its lunar program in the wrong direction—letting deficiencies in the hardware dictate the level of mission risk.  Early diagram of Gateway. Note that the segment marked 'human lander system' now dwarfs the space station. IV. Gateway I suppose at some point we have to talk about Gateway. Gateway is a small modular space station that NASA wants to build in NRHO. It has been showing up across various missions like a bad smell since before 2012. Early in the Artemis program, NASA described Gateway as a kind of celestial truck stop, a safe place for the lander to park and for the crew to grab a cup of coffee on their way to the moon. But when it became clear that Gateway would not be ready in time for Artemis 3, NASA re-evaluated. Reasoning that two spacecraft could meet up in NRHO just as easily as three, the agency gave permission for the first moon landing to proceed without a space station. Despite this open admission that Gateway is unnecessary, building the space station remains the core activity of the Artemis program. The three missions that follow that first landing are devoted chiefly to Gateway assembly. In fact, initial plans for Artemis 4 left out a lunar landing entirely, as if it were an inconvenience to the real work being done up in orbit. This is a remarkable situation. It’s like if you hired someone to redo your kitchen and they started building a boat in your driveway. Sure, the boat gives the builders a place to relax, lets them practice tricky plumbing and finishing work, and is a safe place to store their tools. But all those arguments will fail to satisfy. You still want to know what building a boat has to do with kitchen repair, and why you’re the one footing the bill. NASA has struggled to lay out a technical rationale for Gateway. The space station adds both cost and complexity to Artemis, a program not particularly lacking in either. Requiring moon-bound astronauts to stop at Gateway also makes missions riskier (by adding docking operations) while imposing a big propellant tax. Aerospace engineer and pundit Robert Zubrin has aptly called the station a tollbooth in space. Even Gateway defenders struggle to hype up the station. A common argument is that Gateway may not ideal for any one thing, but is good for a whole lot of things. But that is the same line of thinking that got us SLS and Orion, both vehicles designed before anyone knew what to do with them. The truth is that all-purpose designs don't exist in human space flight. The best you can do is build a spacecraft that is equally bad at everything. But to search for technical grounds is to misunderstand the purpose of Gateway. The station is not being built to shelter astronauts in the harsh environment of space, but to protect Artemis in the harsh environment of Congress. NASA needs Gateway to navigate an uncertain political landscape in the 2030’s. Without a station, Artemis will just be a series of infrequent multibillion dollar moon landings, a red cape waved in the face of the Office of Management and Budget. Gateway armors Artemis by bringing in international partners, each of whom contributes expensive hardware. As NASA learned building the International Space Station, this combination of sunk costs and international entanglement is a powerful talisman against program death. Gateway also solves some other problems for NASA. It gives SLS a destination to fly to, stimulates private industry (by handing out public money to supply Gateway), creates a job for the astronaut corps, and guarantees the continuity of human space flight once the ISS becomes uninhabitable sometime in the 2030’s. [15] That last goal may sound odd if you don’t see human space flight as an end in itself. But NASA is a faith-based organization, dedicated to the principle that taxpayers should always keep an American or two in orbit. it’s a little bit as if the National Oceanic Atmospheric Administration insisted on keeping bathyscapes full of sailors at the bottom of the sea, irrespective of cost or merit, and kneecapped programs that might threaten the continuous human benthic presence. You can’t argue with faith. From a bureaucrat’s perspective, Gateway is NASA’s ticket back to a golden era in the early 2000's when the Space Station and Space Shuttle formed an uncancellable whole, each program justifying the existence of the other. Recreating this dynamic with Gateway and SLS/Orion would mean predictable budgets and program stability for NASA well into the 2050’s. But Artemis was supposed to take us back to a different golden age, the golden age of Apollo. And so there’s an unresolved tension in the program between building Gateway and doing interesting things on the moon. With Artemis missions two or more years apart, it’s inevitable that Gateway assembly will push aspirational projects like a surface habitat or pressurized rover out into the 2040’s. But those same projects are on the critical path to Mars, where NASA still insists we’re going in the late 2030’s. The situation is awkward. So that is the story of Gateway—unloved, ineradicable, and as we’ll see, likely to become the sole legacy of the Artemis program.  V. The Lander The lunar lander is the most technically ambitious part of Artemis. Where SLS, Orion, and Gateway are mostly a compilation of NASA's greatest hits, the lander requires breakthrough technologies with the potential to revolutionize space travel. Of course, you can’t just call it a lander. In Artemis speak, this spacecraft is the Human Landing System, or HLS. NASA has delegated its design to two private companies, Blue Origin and SpaceX. SpaceX is responsible for landing astronauts on Artemis 3 and 4, while Blue Origin is on the hook for Artemis 5 (notionally scheduled for 2030). After that, the agency will take competitive bids for subsequent missions. The SpaceX HLS design is based on their experimental Starship spacecraft, an enormous rocket that takes off on and lands on its tail, like 1950’s sci-fi. There is a strong “emperor’s new clothes” vibe to this design. On the one hand, it is the brainchild of brilliant SpaceX engineers and passed NASA technical review. On the other hand, the lander seems to go out of its way to create problems for itself to solve with technology. An early SpaceX rendering of the Human Landing System, with the Apollo Lunar Module added for scale. To start with the obvious, HLS looks more likely to tip over than the last two spacecraft to land on the moon, which tipped over. It is a fifteen story tower that must land on its ass in terrible lighting conditions, on rubble of unknown composition, over a light-second from Earth. The crew are left suspended so high above the surface that they need a folding space elevator (not the cool kind) to get down. And yet in the end this single-use lander carries less payload (both up and down) than the tiny Lunar Module on Apollo 17. Using Starship to land two astronauts on the moon is like delivering a pizza with an aircraft carrier. Amusingly, the sheer size of the SpaceX design leaves it with little room for cargo. The spacecraft arrives on the Moon laden with something like 200 tons of cryogenic propellant,[16] and like a fat man leaving an armchair, it needs every drop of that energy to get its bulk back off the surface. Nor does it help matters that all this cryogenic propellant has to cook for a week in direct sunlight. Other, less daring lander designs reduce their appetite for propellant by using a detachable landing stage. This arrangement also shields the ascent rocket from hypervelocity debris that gets kicked up during landing. But HLS is a one-piece rocket; the same engines that get sandblasted on their way down to the moon must relight without fail a week later. Given this fact, it’s remarkable that NASA’s contract with SpaceX doesn’t require them to demonstrate a lunar takeoff. All SpaceX has to do to satisfy NASA requirements is land an HLS prototype on the Moon. Questions about ascent can then presumably wait until the actual mission, when we all find out together with the crew whether HLS can take off again.[17] This fearlessness in design is part of a pattern with Starship HLS. Problems that other landers avoid in the design phase are solved with engineering. And it’s kind of understandable why SpaceX does it this way. Starship is meant to fly to Mars, a much bigger challenge than landing two people on the moon. If the basic Starship design can’t handle a lunar landing, it would throw the company’s whole Mars plan into question. SpaceX is committed to making Starship work, which is different from making the best possible lunar lander. Less obvious is why NASA tolerates all this complexity in the most hazardous phase of its first moon mission. Why land a rocket the size of a building packed with moving parts? It’s hard to look at the HLS design and not think back to other times when a room full of smart NASA people talked themselves into taking major risks because the alternative was not getting to fly at all. It’s instructive to compare the HLS approach to the design philosophy on Apollo. Engineers on that progam were motivated by terror; no one wanted to make the mistake that would leave astronauts stranded on the moon. The weapon they used to knock down risk was simplicity. The Lunar Module was a small metal box with a wide stance, built low enough so that the astronauts only needed to climb down a short ladder. The bottom half of the LM was a descent stage that completely covered the ascent rocket (a design that showed its value on Apollo 15, when one of the descent engines got smushed by a rock). And that ascent rocket, the most important piece of hardware in the lander, was a caveman design intentionally made so primitive that it would struggle to find ways to fail. On Artemis, it's the other way around: the more hazardous the mission phase, the more complex the hardware. It's hard to look at all this lunar machinery and feel reassured, especially when NASA's own Aerospace Safety Advisory Panel estimates that the Orion/SLS portion of a moon mission alone (not including anything to do with HLS) already has a 1:75 chance of killing the crew. VI. Refueling Since NASA’s biggest rocket struggles to get Orion into distant lunar orbit, and HLS weighs fifty times as much as Orion, the curious reader might wonder how the unmanned lander is supposed to get up there. NASA’s answer is, very sensibly, “not our problem”. They are paying Blue Origin and SpaceX the big bucks to figure this out on their own. And as a practical matter, the only way to put such a massive spacecraft into NRHO is to first refuel it in low Earth orbit. Like a lot of space technology, orbital refueling sounds simple, has never been attempted, and can’t be adequately simulated on Earth.[18] The crux of the problem is that liquid and gas phases in microgravity jumble up into a three-dimensional mess, so that even measuring the quantity of propellant in a tank becomes difficult. To make matters harder, Starship uses cryogenic propellants that boil at temperatures about a hundred degrees colder than the plumbing they need to move through. Imagine trying to pour water from a thermos into a red-hot skillet while falling off a cliff and you get some idea of the difficulties. To get refueling working, SpaceX will first have to demonstrate propellant transfer between rockets as a proof of concept, and then get the process working reliably and efficiently at a scale of hundreds of tons. (These are two distinct challenges). Once they can routinely move liquid oxygen and methane from Starship A to Starship B, they’ll be ready to set up the infrastructure they need to launch HLS. The plan for getting HLS to the moon looks like this: a few months before the landing date, SpaceX will launch a special variant of their Starship rocket configured to serve as a propellant depot. Then they'll start launching Starships one by one to fill it up. Each Starship arrives in low Earth orbit with some residual propellant; it will need to dock with the depot rocket and transfer over this remnant fuel. Once the depot is full, SpaceX will launch HLS, have it fill its tanks at the depot rocket, and send it up to NRHO in advance of Orion. When Orion arrives, HLS will hopefully have enough propellant left on board to take on astronauts and make a single round trip from NRHO to the lunar surface. Getting this plan to work requires solving a second engineering problem, how to keep cryogenic propellants cold in space. Low earth orbit is a toasty place, and without special measures, the cryogenic propellants Starship uses will quickly vent off into space. The problem is easy to solve in deep space (use a sunshade), but becomes tricky in low Earth orbit, where a warm rock covers a third of the sky. (Boil-off is also a big issue for HLS on the moon.) It’s not clear how many Starship launches it will take to refuel HLS. Elon Musk has said four might be enough; NASA Assistant Deputy Associate Administrator Lakiesha Hawkins says the number is in the “high teens”. Last week, SpaceX's Kathy Lueders gave a figure of fifteen launches. The real number is unknown and will come down to four factors: How much propellant a Starship can carry to low Earth orbit. What fraction of that can be usably pumped out of the rocket. How quickly cryogenic propellant boils away from the orbiting depot. How rapidly SpaceX can launch Starships. SpaceX probably knows the answer to (1), but isn’t talking. Data for (2) and (3) will have to wait for flight tests that are planned for 2025. And obviously a lot is riding on (4), also called launch cadence. The record for heavy rocket launch cadence belongs to the Space Shuttle, which flew nine times in the calendar year before the Challenger disaster. Second place belongs to the Saturn V, which launched three times during a four and a half month period in 1969. In third place is Falcon Heavy, which flew six times in a 13 month period beginning in November 2022. For the refueling plan to work, Starship will have to break this record by a factor of ten, launching every six days or so across multiple launch facilities. [19] The refueling program can tolerate a few launch failures, as long as none of them damages a launch pad. There’s no company better prepared to meet this challenge than SpaceX. Their Falcon 9 rocket has shattered records for both reliability and cadence, and now launches about once every three days. But it took SpaceX ten years to get from the first orbital Falcon 9 flight to a weekly cadence, and Starship is vastly bigger and more complicated than the Falcon 9. [20] Working backwards from the official schedule allows us to appreciate the time pressure facing SpaceX. To make the official Artemis landing date, SpaceX has to land an unmanned HLS prototype on the moon in early 2026. That means tanker flights to fill an orbiting depot would start in late 2025. This doesn’t leave a lot of time for the company to invent orbital refueling, get it working at scale, make it efficient, deal with boil-off, get Starship launching reliably, begin recovering booster stages,[21] set up additional launch facilities, achieve a weekly cadence, and at the same time design and test all the other systems that need to go into HLS. Lest anyone think I’m picking on SpaceX, the development schedule for Blue Origin’s 2029 lander is even more fantastical. That design requires pumping tons of liquid hydrogen between spacecraft in lunar orbit, a challenge perhaps an order of magnitude harder than what SpaceX is attempting. Liquid hydrogen is bulky, boils near absolute zero, and is infamous for its ability to leak through anything (the Shuttle program couldn't get a handle on hydrogen leaks on Earth even after a hundred some launches). And the rocket Blue Origin needs to test all this technology has never left the ground. The upshot is that NASA has put a pair of last-minute long-shot technology development programs between itself and the moon. Particularly striking is the contrast between the ambition of the HLS designs and the extreme conservatism and glacial pace of SLS/Orion. The same organization that spent 23 years and 20 billion dollars building the world's most vanilla spacecraft demands that SpaceX darken the sky with Starships within four years of signing the initial HLS contract. While thrilling for SpaceX fans, this is pretty unserious behavior from the nation’s space agency, which had several decades' warning that going to the moon would require a lander. All this to say, it's universally understood that there won’t be a moon landing in 2026. At some point NASA will have to officially slip the schedule, as it did in 2021, 2023, and at the start of this year. If this accelerating pattern of delays continues, by year’s end we might reach a state of continuous postponement, a kind of scheduling singularity where the landing date for Artemis 3 recedes smoothly and continuously into the future. Otherwise, it's hard to imagine a manned lunar landing before 2030, if the Artemis program survives that long. VII. Conclusion I want to stress that there’s nothing wrong with NASA making big bets on technology. Quite the contrary, the audacious HLS contracts may be the healthiest thing about Artemis. Visionaries at NASA identified a futuristic new energy source (space billionaire egos) and found a way to tap it on a fixed-cost basis. If SpaceX or Blue Origin figure out how to make cryogenic refueling practical, it will mean a big step forward for space exploration, exactly the thing NASA should be encouraging. And if the technology doesn’t pan out, we’ll have found that out mostly by spending Musk’s and Bezos’s money. The real problem with Artemis is that it doesn’t think through the consequences of its own success. A working infrastructure for orbital refueling would make SLS and Orion superfluous. Instead of waiting two years to go up on a $4 billion rocket, crews and cargo could launch every weekend on cheap commercial rockets, refueling in low Earth orbit on their way to the moon. A similar logic holds for Gateway. Why assemble a space station out of habitrail pieces out in lunar orbit, like an animal, when you can build one on Earth and launch it in one piece? Better yet, just spraypaint “GATEWAY” on the side of the nearest Starship, send it out to NRHO, and save NASA and its international partners billions. Having a working gas station in low Earth orbit fundamentally changes what is possible, in a way the SLS/Orion arm of Artemis doesn't seem to recognize. Conversely, if SpaceX and Blue Origin can’t make cryogenic refueling work, then NASA has no plan B for landing on the moon. All the Artemis program will be able to do is assemble Gateway. Promising taxpayers the moon only to deliver ISS Jr. does not broadcast a message of national greatness, and is unlikely to get Congress excited about going to Mars. The hurtful comparisons between American dynamism in the 1960’s and whatever it is we have now will practically write themselves. What NASA is doing is like an office worker blowing half their salary on lottery tickets while putting the other half in a pension fund. If the lottery money comes through, then there was really no need for the pension fund. But without the lottery win, there’s not enough money in the pension account to retire on. The two strategies don't make sense together. There’s a ‘realist’ school of space flight that concedes all this but asks us to look at the bigger picture. We’re never going to have the perfect space program, the argument goes, but the important thing is forward progress. And Artemis is the first program in years to survive a presidential transition and have a shot at getting us beyond low Earth orbit. With Artemis still funded, and Starship making rapid progress, at some point we’ll finally see American astronauts back on the moon. But this argument has two flaws. The first is that it feeds a cycle of dysfunction at NASA that is rapidly making it impossible for us to go anywhere. Holding human space flight to a different standard than NASA’s science missions has been a disaster for space exploration. Right now the Exploration Systems Development Mission Directorate (the entity responsible for manned space flight) couldn’t build a toaster for less than a billion dollars. Incompetence, self-dealing, and mismanagement that end careers on the science side of NASA are not just tolerated but rewarded on the human space flight side. Before we let the agency build out its third white elephant project in forty years, it’s worth reflecting on what we're getting in return for half our exploration budget. The second, more serious flaw in the “realist” approach is that it enables a culture of institutional mendacity that must ultimately be fatal at an engineering organization. We've reached a point where NASA lies constantly, to both itself and to the public. It lies about schedules and capabilities. It lies about the costs and the benefits of its human spaceflight program. And above all, it lies about risk. All the institutional pathologies identified in the Rogers Report and the Columbia Accident Investigation Board are alive and well in Artemis—groupthink, management bloat, intense pressure to meet impossible deadlines, and a willingness to manufacture engineering rationales to justify flying unsafe hardware. Do we really have to wait for another tragedy, and another beautifully produced Presidential Commission report, to see that Artemis is broken? Notes [1] Without NASA's help, it's hard to put a dollar figure on a mission without making somewhat arbitrary decisions about what to include and exclude. The $7-10 billion estimate comes from a Bush-era official in the Office of Management and Budget commenting on the NASA Spaceflight Forum And that $7.2B assumes Artemis III stays on schedule. Based on the FY24 budget request, each additional year between Artemis II and Artemis III adds another $3.5B to $4.0B in Common Exploration to Artemis III. If Artemis III goes off in 2027, then it will be $10.8B total. If 2028, then $14.3B. In other words, it's hard to break out an actual cost while the launch dates for both Artemis II and III keep slipping. NASA's own Inspector General estimates the cost of just the SLS/Orion portion of a moon landing at $4.1 billion. [2] The first US suborbital flight, Friendship 7, launched on May 15, 1961. Armstrong and Aldrin landed on the moon eight years and two months later, on July 21, 1969. President Bush announced the goal of returning to the moon in a January 2004 speech, setting the target date for the first landing "as early as 2015", and no later than 2020. [3] NASA refuses to track the per-launch cost of SLS, so it's easy to get into nerdfights. Since the main cost driver on SLS is the gigantic workforce employed on the project, something like two or three times the headcount of SpaceX, the cost per launch depends a lot on cadence. If you assume a yearly launch rate (the official line), then the rocket costs $2.1 billion a launch. If like me you think one launch every two years is optimistic, the cost climbs up into the $4-5 billion range. [4] The SLS weighs 2,600 metric tons fully fueled, and conveniently enough a dollar bill weighs about 1 gram. [5] SpaceX does not disclose the cost, but it's widely assumed the Raptor engine used on Superheavy costs $1 million. [6] The $145 million figure comes from dividing the contract cost by the number of engines, caveman style. Others have reached a figure of $100 million for the unit cost of these engines. The important point is not who is right but the fact that NASA is paying vastly more than anyone else for engines of this class. [7] $250M is the figure you get by dividing the $3.2 billion Booster Production and Operations contract to Northrop Grumman by the number of boosters (12) in the contract. Source: Office of the Inspector General. For cost overruns replacing asbestos, see the OIG report on NASA’s Management of the Space Launch System Booster and Engine Contracts. The Department of Defense paid $130 million for a Falcon Heavy launch in 2023. [8] Rocket Lab developed, tested, and flew its Electron rocket for a total program cost of $100 million. [9] In particular, the separation bolts embedded in the Orion heat shield were built based on a flawed thermal model, and need to be redesigned to safely fly a crew. From the OIG report: Separation bolt melt beyond the thermal barrier during reentry can expose the vehicle to hot gas ingestion behind the heat shield, exceeding Orion’s structural limits and resulting in the breakup of the vehicle and loss of crew. Post-flight inspections determined there was a discrepancy in the thermal model used to predict the bolts’ performance pre-flight. Current predictions using the correct information suggest the bolt melt exceeds the design capability of Orion. The current plan is to work around these problems on Artemis 2, and then redesign the components for Artemis 3. That means astronauts have to fly at least twice with an untested heat shield design. [10] Orion/ESM has a delta V budget of 1340 m/s. Getting into and out of an equatorial low lunar orbit takes about 1800 m/s, more for a polar orbit. (See source.) [11] It takes about 900 m/s of total delta V to get in and out of NHRO, comfortably within Orion/ESM's 1340 m/s budget. (See source.) [12] In Carrying the Fire, Apollo 11 astronaut Michael Collins recalls carrying a small notebook covering 18 lunar rendezvous scenarios he might be called on to fly in various contingencies. If the Lunar Module could get itself off the surface, there was probably a way to dock with it. For those too young to remember, Tang is a powdered orange drink closely associated with the American space program. [13] For a detailed (if somewhat cryptic) discussion of possible Artemis abort modes to NRHO, see HLS NRHO to Lunar Surface and Back Mission Design, NASA 2022. [14] The main safety issue is the difficult thermal environment at the landing site, where the Sun sits just above the horizon, heating half the lander. If it weren't for the NRHO constraint, it's very unlikely Artemis 3 would spend more than a day or two on the lunar surface. [15] The ISS program has been repeatedly extended, but the station is coming up against physical limiting factors (like metal fatigue) that will soon make it too dangerous to use. [16] This is my own speculative guess; the answer is very sensitive to the dry weight of HLS and the boil-off rate of its cryogenic propellants. Delta V from the lunar surface to NRHO is 2,610 m/sec. Assuming HLS weighs 120 tons unfueled, it would need about 150 metric tons of propellant to get into NRHO from the lunar surface. Adding safety margin, fuel for docking operations, and allowing for a week of boiloff gets me to about 200 tons. [17] Recent comments by NASA suggest SpaceX has voluntarily added an ascent phase to its landing demo, ending a pretty untenable situation. However, there's still no requirement that the unmanned landing/ascent demo be performed using the same lander design that will fly on the actual mission, another oddity in the HLS contract. [18] To be precise, I'm talking about moving bulk propellant between rockets in orbit. There are resupply flights to the International Space Station that deliver about 850 kilograms of non-cryogenic propellant to boost the station in its orbit, and there have been small-scale experiments in refueling satellites. But no one has attempted refueling a flown rocket stage in space, cryogenic or otherwise. [19] Both SpaceX's Kathy Lueders and NASA confirm Starship needs to launch from multiple sites. Here's an excerpt from the minutes of the NASA Advisory Council Human Exploration and Operations Committee meeting on November 17 and 20, 2023: Mr. [Wayne] Hale asked where Artemis III will launch from. [Assistant Deputy AA for Moon to Mars Lakiesha] Hawkins said that launch pads will be used in Florida and potentially Texas. The missions will need quite a number of tankers; in order to meet the schedule, there will need to be a rapid succession of launches of fuel, requiring more than one site for launches on a 6-day rotation schedule, and multiples of launches. [20] Falcon 9 first flew in June of 2010 and achieved a weekly launch cadence over a span of six launches starting in November 2020. [21] Recovering Superheavy stages is not a NASA requirement for HLS, but it's a huge cost driver for SpaceX given the number of launches involved.

For a successful technology, reality must take precedence over public relations, for nature cannot be fooled. — Richard Feynman Entrance to underground cavern on Pavonis Mons. HiRISE, 2011 The goal of this essay is to persuade you that we shouldn’t send human beings to Mars, at least not anytime soon. Landing on Mars with existing technology would be a destructive, wasteful stunt whose only legacy would be to ruin the greatest natural history experiment in the Solar System. It would no more open a new era of spaceflight than a Phoenician sailor crossing the Atlantic in 500 B.C. would have opened up the New World. And it wouldn’t even be that much fun. The buildup to Mars would not look like Apollo, but a long series of ISS-like flights to nowhere. If your main complaint about the International Space Station is that it’s too exciting and has a distracting view of Earth out the window, then you’ll love watching ISS Jr. drift around doing bone studies in deep space. But if you think rockets, adventure, exploration, and discovery are more fun than counting tumors in mice, then the slow and timorous Mars program will only break your heart. Sticking a flag in the Martian dust would cost something north of half a trillion dollars [1], with no realistic prospect of landing before 2050 [2]. To borrow a quote from John Young, keeping such a program funded through fifteen consecutive Congresses would require a series “of continuous miracles, interspersed with acts of God”. [3] Like the Space Shuttle and Space Station before it, the Mars program would exist in a state of permanent redesign by budget committee until any logic or sense in the original proposal had been wrung out of it. When the great moment finally came, and the astronauts had taken their first Martian selfie, strict mission rules meant to prevent contamination and minimize risk would leave the crew dependent on the same robots they’d been sent at enormous cost to replace. Only the microbes that lived in the spacecraft, uninformed of the mission rules, would be free to go wander outside. They would become the real explorers of Mars, and if their luck held, its first colonists. How long such a program could last is anyone’s guess. But if landing on the Moon taught us anything, it’s that taxpayer enthusiasm for rock collecting has hard limits. At ~$100B per mission, and with launch windows to Mars one election cycle apart [4], NASA would be playing a form of programmatic Russian roulette. It’s hard to imagine landings going past the single digits before cost or an accident shut the program down. And once the rockets had retired to their museums, humanity would have nothing to show for its Mars adventure except some rocks and a bunch of unspeakably angry astrobiologists. It would in every way be the opposite of exploration. Polar sand dunes, HiRISE, 2009 It wasn’t always like this. There was a time when going to Mars made sense, back when astronauts were a cheap and lightweight alternative to costly machinery, and the main concern about finding life on Mars was whether all the trophy pelts could fit in the spacecraft. No one had been in space long enough to discover the degenerative effects of freefall, and it was widely accepted that not just exploration missions, but complicated instruments like space telescopes and weather satellites, were going to need a permanent crew [5]. But fifty years of progress in miniaturization and software changed the balance between robots and humans in space. Between 1960 and 2020, space probes improved by something like six orders of magnitude[6], while the technologies of long-duration spaceflight did not. Boiling the water out of urine still looks the same in 2023 as it did in 1960, or for that matter 1060. Today’s automated spacecraft are not only strictly more capable[7] than human astronauts, but cost about a hundred times less [8] to send (though it’s hard to be exact, since astronauts have not gone anywhere since 1972[9]). The imbalance between human and robot is so overwhelming that, despite the presence of a $250 billion[10] International Space Station National Laboratory, every major discovery made in space this century has come from robotic spacecraft [11]. In 2023, we simply take it for granted that if a rocket goes up carrying passengers, it’s not going to get any work done. As for that space station, the jewel of human spaceflight, it exists in a state of nearly perfect teological closure, its only purpose being to teach its creators how to build future spacecraft like it. The ISS crew spend most of their time fixing the machinery that keeps them alive, and when they have a free moment for science, they tend to study the effect of space on themselves. At 22 years old [12], the ISS is still as dependent on fresh meals and clean laundry sent from home as the most feckless grad student. And yet this orbiting end-in-itself is also the closest we’ve come to building an interplanetary spacecraft. The idea of sending something like it on a three year journey to Mars does not get engineers’ hearts racing, at least not in the good way. Mars in the springtime. The dots and dark lines are conjectured to be flow phenomena connected with sublimating dry ice. HiRISE, 2008 Mars is also not the planet we took it for. The first photos Mariner 4 sent back in 1965 were shocking; instead of bucolic canals they showed a waterless, cratered wasteland not much different from the Moon. Ten years later, the Viking landers confirmed that Mars was a frozen, desiccated world bathed in sterilizing radiation, where any Earth creature that arrived unprotected would be dead before it hit the ground. But as orbiters started arriving in the 2000’s, Mars got a glow-up. The surface might be dry, but in most places there was water ice just underneath. Dynamic surface features hinted that water (or at least brine) was flowing to the surface from deep underground. In 2020, radar surveys found evidence of at least two subglacial lakes[13] under the south polar cap, strongly implying a reservoir of geothermal heat[14]. And earlier this month, an article in Nature announced the discovery of an active mantle plume[15] below Elysium Planitia, catapulting Mars onto the VIP list of geologically active worlds. The news from the ground also got better. Arriving at Gale Crater in 2012, the Curiosity rover found itself looking at an ordinary lake bed, complete with organic sediment and odd stick-like structures[16] that would be called fossils if we found them on Earth. The crater had been habitable for millions of years[17] in the past, and something in it was still emitting methane at night[18]. Over in its own crater, the Perseverance rover found complex organic molecules of indeterminate origin. Sand dunes, HiRISE 2016 But the really exciting news for Mars was the discovery of unexpected life on Earth. Microbiologists had long suspected that the 12,000 or so[19] known species of microbes were just a fraction of the total, with perhaps another hundred thousand[20] “unculturable” species left to discover. But when new sequencing technology became available at the turn of the century, it showed the number of species might be as high as one trillion [21]. In the genomic gold rush that followed, researchers discovered not just dozens of unsuspected microbial phyla[22], but two entire new branches of life[23]. These new techniques confirmed that earth’s crust is inhabited to a depth of kilometers by a ‘deep biosphere’ of slow-living microbes nourished by geochemical processes and radioactive decay. One group of microbes was discovered still living their best lives[24] 100 million years after being sealed in sedimentary rock. Another was found enjoying a rewarding, long-term relationship with fungal partners deep beneath the seafloor[25]. This underground ecology, which we have barely started to explore, might account for a third[26] of the biomass on earth. Our family tree, circa 2016. Branches with red dots are ones we know nothing about. Another 1,300 microbial phyla may remain undiscovered [27]. You and I are in the bottom right corner. At this point, it is hard to not find life on Earth. Microbes have been discovered living in cloud tops[28], inside nuclear reactor cores[29], and in aerosols high in the stratosphere[30]. Bacteria not only stay viable for years on the space station hull, but sometimes do better out there[31] than inside the spacecraft. Environments long thought to be sterile, like anoxic brines at the bottom of the Mediterranean sea[32], are in fact as rich in microbial life as a gas station hot dog. Even microbes trapped for millions of years in salt crystals[33] or Antarctic ice[34] have shown they can wake up and get back to metabolizing[35] without so much as a cup of coffee. The fact that we failed to notice 99.999% of life on Earth until a few years ago is unsettling and has implications for Mars. The existence of a deep biosphere in particular narrows the habitability gap between our planets to the point where it probably doesn’t exist—there is likely at least one corner of Mars that an Earth organism could call home. It also adds support to the theory that life may have started as an interplanetary infection, a literal Venereal disease that spread across the early solar system by meteorite[36]. If that is the case, and if our distant relatives are still alive in some deep Martian cave, then just about the worst way to go looking for them would be to land in a septic spacecraft. Dust devil tracks on Mars. What causes the dark parallel lines is still unknown. HiRISE, 2009. But the fact that a Mars landing stopped making sense has not had the slightest impact on NASA’s plan to go there in a rocket-propelled terrarium. Though facts may change, and technology may change, one thing will always remain the same—we’re going to Mars, 1950’s style. It is difficult to get NASA leadership to explain the purpose of this mission, not because they're obdurate, but because they seem genuinely confused by the question. We’ve already been to the Moon, and Mars comes after the Moon. What part of that is not clear? The idea that a human landing might be in tension with other forms of exploration, or that the might need to make a case for the mission, does not enter into their thinking. Last summer, at a press briefing on the Moon to Mars program[37], a journalist asked NASA Administrator Bill Nelson to explain to Americans in plain language why NASA wanted to send astronauts to Mars and to the Moon. His reply is worth quoting in full: “This is what I would tell them. First of all, we are explorers and adventurers as a species. That basically is the fulfilment of our destiny. But, in that exploration, we’re going to learn new things and develop new things that is going to improve, just as it’s been under our space program, our lives here on Earth. Last week I was in Kansas, I was with a corn farmer, where we are giving him real time information on the moisture content of the soil in this crop and next to it, that crop, so that he knows what to plant. Those instruments obviously for example can pick up disease, pick up disease in forest that then become susceptible to fire. That certainly is going to help our life here on Earth. And those are things that have come out of the space program, things that we can’t even think of. But there’s more. When we go to Mars in the late 30’s[38], just think how much more we’re going to understand about our Solar System, and about the Universe, as a result of things like many of our instruments out there, not the least of which is the James Webb Space Telescope. We may have by that time found an asteroid that we don’t have to protect Earth on, as we want to try with DART in another month, but we may find an asteroid that has valuable materials on it, metals, that we can harvest. By 2040, we may have detected life elsewhere in the universe. And think what that’s going to do in our yearning for exploration. So I can’t answer specifically the question, “what happens after Mars?” I just know we’re going to know a lot more between now and then. And our discoveries and our exploration are going to continue. And the apt analogy was given by [Associate Administrator] Bhavya [Lal]. When Thomas Jefferson sent Lewis and Clark all the way to the Pacific coast, look what happened as a result! I include Nelson’s full remarks because this is the most substantive explanation I’ve found from NASA for their Mars landing. [40] Note that none of the programs he references (Global Agricultural Monitoring, DART, Landsat, the Webb Space Telescope, and TESS) have any connection to human spaceflight, let alone Mars. The only parts of this answer that apply to Mars are the bits about destiny, exploration, and Lewis and Clark (who I have to stress were looking for an ocean of liquid water). If the head of NOAA Ocean Exploration (budget: $25 million) or the U.S. Antarctic Program ($350 million) held a press conference announcing a plan to fulfill human destiny, they’d be carrying their belongings home in a cardboard box before sundown. But our space agency is held to a lower standard. All this would be fine if it was just talk. But NASA spent more on their Moon and Mars programs in 2022[41] than the total budget of the National Science Foundation[42]. And in 2024, they plan to start launching pieces of a new space station, the Gateway, which by the laws of orbital bureaucracy will lock us in to decades of having to invent reasons to go visit the thing. Somehow we’ve embarked on the biggest project in history even though it has no articulable purpose, offers no benefits, and will cost taxpayers more than a good-sized war. Even the builders of the Great Pyramid at Giza could at least explain what it was for. And yet this project has sailed through an otherwise gridlocked system with the effortlessness of a Pentagon budget. Presidents of both parties now make landing on Mars an official goal of US space policy. Even billionaires who made their fortune automating labor on Earth agree that Mars must be artisanally explored by hand. The whole thing is getting weird. Volunteers carry out a mock mission at the Mars Desert Research Station in Utah (photo: Brian van der Brug) The Mars Religion When you hold on to a belief so strongly that neither facts nor reason can change it, what you are doing is no longer science, but religion. So I’ve come to believe the best way to look at our Mars program is as a faith-based initiative. There is a small cohort of people who really believe in going to Mars, the way some people believe in ghosts or cryptocurrency, and this group has an outsize effect on our space program. At NASA, the faith takes the form of a cargo cult. The agency has persuaded itself that re-enacting the Moon landings with enough fidelity will reward them with a trip to Mars, bringing back the limitless budgets, uncomplicated patriotism, and rapt public attention of the early sixties. They send up their rockets with the same touching faith that keeps Amtrak hauling empty dining cars across the prairie, dreaming of the golden age of rail. Outside of NASA, the Mars faith shades darker. It is part of a transhumanist worldview that holds mankind must either spread to the stars or die. Elon Musk, the Martian spiritual leader, has talked about the need to “preserve the light of consciousness” by making us a multiplanetary species. As he sees it, Mars is our only way off of a planet crawling with existential risk. And it's not just enough to explore mars; we have make it a backup for all civilization. Failing to stock it with subsistence farming incels would be tantamount to humanity lying down in its open grave. That is some heavy stuff to lay on a small, rocky world. I think it’s time we brought the Mars talk down to earth, and started approaching a landing there as an aerospace project rather than the fulfillment of God’s plan. But so far, public discourse on Mars has mostly been about whose rocket is bigger and which billionaire can get his up the fastest. Since we’re already paying for this program, why not look at it in more detail? It's pretty clear what a Mars mission would look like, how long it would take, and where the big technology gaps are. We’ve learned a great deal about Mars itself, and have twenty years of ISS technical reports to work from. So let's have ourselves a good old fashioned nerdfight. In what follows, I want to lay out the case against Mars in more technical detail than I’ve been able to find elsewhere. Then we can argue about it online, on the merits, like space nerds used to. The argument I’ll make has three parts: 1. Research Astronaut Karen Nyberg performs an eye exam on the ISS in 2013 The things that make going to Mars hard are not fun space things, like needing a bigger rocket, but tedious limits of human physiology. Understanding these limits well enough to get to Mars will require years of human experiments beyond low Earth orbit[43]. In particular, we need preliminary data on the physiological effects of partial gravity,[44] and a better estimate of the risk from heavy ion radiation[45]. Since core tradeoffs around crew safety depend on the outcome, these experiments have to be done before NASA can finalize a mission design. Absent a miracle in appropriations, the only practical place to do this research will be on the Moon[46]. This puts a working lunar base on the critical path to a Mars landing, and means any delay or snag in NASA’s Artemis program automatically pushes back the earliest date for a Mars landing. This research gap is what makes it impossible to get to Mars quickly, even with unlimited funding[47]. Unless you’re willing to risk the safety of the crew, there’s no way to avoid watching astronauts sit around on the Moon for a few years with their Geiger counters out. 2. Engineering Italian astronaut Samantha Cristoforetti tests ISSpresso, her country's contribution to the ISS life support system, in 2015 The chief technical obstacle to a Mars landing is not propulsion, but a lack of reliable closed-loop life support[48]. With our current capability, NASA would struggle to keep a crew alive for six months on the White House lawn, let alone for years in a Martian yurt. The technology program required to close this gap would be remarkably circular, with no benefits outside the field of applied zero gravity zookeeping. The web of Rube Goldberg devices that recycles floating animal waste on the space station has already cost twice its weight in gold[49] and there is little appetite for it here on Earth, where plants do a better job for free. I would compare keeping primates alive in spacecraft to trying to build a jet engine out of raisins. Both are colossal engineering problems, possibly the hardest ever attempted, but it does not follow that they are problems worth solving. In both cases, the difficulty flows from a very specific design constraint, and it’s worth revisiting that constraint one or ten times before starting to perform miracles of engineering. What makes life support so vexing is that all the subcomponents interact with each other and with the crew. There’s no such thing as a life support unit test; you have to run the whole system in space under conditions that mimic the target mission. Reliability engineering for life support involves solving mysteries like why gunk formed on a certain washer on Day 732, then praying on the next run that your fix doesn’t break on Day 733. The process repeats until the first crew makes it home alive (figuratively speaking), at which point you declare the technology reliable and chill the champagne. Unlike the medical research, there’s no way to predict how long these trials might take. A typical exploration profile[50] needs two different kinds of life support (for the spacecraft and the surface) that together have to work for about 1000 days. The spacecraft also has to demonstrate that it can go dormant for the time the crew is on Mars and still work when it wakes up. Twenty years of tinkering with the much simpler systems on the space station have brought them no closer to reliability. And yet to get a crew to Mars, we’d need to get this stuff working like a Swiss watch. Humanity does not need a billion dollar shit dehydrator that can work for three years in zero gravity, but a Mars mission can’t leave Earth without it. 3. Contamination Debris left by the Perserverance landing, photographed in April 2022 by the Ingenuity helicopter. Humans who land on Mars will not be able to avoid introducing a large ecosystem of microbes to the area around the landing site. If any fugitives from the spacecraft make their way to a survivable niche on Mars, we may never be able to tell whether biotic signatures later found on the planet are traces of native life, or were left by escapees from our first Martian outhouse. Like careless investigators who didn’t wear gloves to a crime scene, we would risk permanently destroying the evidence we came to collect. “No exploration without contamination” would be a good phrase to stencil in red letters above the airlock (ideally before welding it shut). Contamination risk is a real showstopper for Mars, one of those problems that gets worse the more carefully you look at it. It should put the planet off limits to human explorers until we’re either sure that there is no pathway from the spacecraft to a habitable Martian environment, or are confident for other reasons that the consequences don’t matter[51]. Even the astronaut corps recognizes that exploring Mars and keeping it pristine are irreconcilable activities, like trying to drill for oil in a cleanroom. The problem goes beyond practical questions like how to store 17 months of astronaut shit and gets to the crux of the matter: why is bringing a leaky, bacteria-filled terrarium to Mars step one[52] in our search for Martian life? What incredible ability do astronauts have that justifies taking this risk? Skeptics point out that Earth microbes have already landed on Mars, both on robotic landers[53] and the occasional meteorite. But as we’ll see, the diverse microbiome that would travel with a human crew poses a qualitatively different threat[54], and would have a far better chance of getting settled on Mars, than the sad loners clinging to rovers like Curiosity. Even if you don’t care about contamination, NASA is required by treaty to care[55], and that has severe consequences for mission design. It means human landing sites will intentionally be kept far from anything interesting. The phenomena of greatest scientific interest on Mars (gullies, recurrent slope lineae, intermittent methane sources, and underground water) will all be off-limits to astronauts. So will terrain features like caves or lava tubes that could conceivably shelter life. The crew will not live in a Martian pueblo, but something resembling a level 4 biocontainment facility[56]. And even there, they’ll have to do their lab work remotely, the same way it’s done today, raising the question of what exactly the hundreds of billions of dollars we’re spending to get to Mars are buying us. Ice near Ultimi Scopuri. ESA/Mars Express, 2022 That’s my case against Mars in a nutshell: it comes front-loaded with expensive research, the engineering is mostly port-a-potty chemistry, and the best-case outcome is that thirty years from now, we’ll get to watch someone remotely operate a soil scoop from Mars instead of Pasadena. I understand not wanting to let go of a cherished dream. But I also have a cherished dream, which is to see space exploration happen in my lifetime. And it is hard to overlook that the $93 billion[57] NASA has already spent through 2025 to not land anyone on the Moon would be enough[58] to send probes to every world in the solar system, including moons we know have oceans of liquid water[59] and two entire planetary systems that haven’t been visited since Voyager 2 gave them a quick once-over in the 1980’s.[60] And let’s not forget Mars! For my part, I would love to know what causes recurrent slope lineae, why there is methane at Gale Crater, and whether anything is swimming in the subsurface lakes discovered in 2018. Orbiters have already found dozens of creepy caves and pits, any one of which would be worth looking into. And the discovery that Mars is geologically active should inspire a search for life deep underground. Exploring these environments remotely won’t be easy, but whatever technology we invent to do it will pay dividends on missions across the solar system. Polar dunes showing carbon dioxide frost and sublimation phenomena, HiRISE 2007 ON THIS PLANET WE BELIEVE IN SCIENCE We’re at a rare moment when the United States is in between white elephant space projects. The ISS is nearing the end of its life[61], and tensions between NASA and Roscosmos have filled all hearts with hope that we can soon drop the thing into the ocean. For the first time since Nixon, Americans have a chance to choose a bolder future for their space program. One path forward would be to build on the technological revolution of the past fifty years and go explore the hell out of space with robots. This future is available to us right now. Simply redirecting the $11.6 billion budget[62] for human space flight would be enough to staff up the Jet Propulsion Laboratory and go from launching one major project per decade to multiple planetary probes and telescopes a year[63]. It would be the start of the greatest era of discovery in history. A different path forward would take us to Mars the slow, dangerous, and hard way. It would take decades and cost hundreds of billions of dollars. It requires developing a solipsistic technology that can’t take us anywhere else except Venus[64]. And it is not guaranteed to work. If there’s a reason this plan is better than going exploring, NASA should articulate it to the people who are going to be paying the bill. NASA has spent decades learning how to survive in the harsh environment of Congress, and that knowledge is bearing fruit today. The machinery that brought us two pointless multibillion dollar space projects has been spun up again to take us to Mars. Like George Lucas preparing to release another awful prequel, NASA is hoping that cool spaceships and nostalgia will be enough to keep everyone from noticing that their story makes no sense. But you can't lie your way to Mars, no matter how sincerely you believe in what you're doing. The Other Mars Program “Mere failure to realize a long-term, aspirational goal is not fraud” —lawyers representing Tesla, November 2022 Of course, in 2022 there is an alternative vision for Mars exploration centered on the activities of Elon Musk. If NASA is Amtrak in space, then SpaceX is the Fyre Festival with rockets, a glamorous effort led by a hype man who promises that every logistical problem will melt away if we can just get people to the destination. What can I say about Musk? He likes rockets and drama, and his approach to every engineering problem is to promise to solve it with cool technology that he’ll have ready in Q2 of next year. This has the effect of turning technical discussions into debates over the character and achievements of Elon Musk— just the way he likes it. SpaceX has built some magnificent rockets, and their dynamism is a welcome change from the souls-trapped-in-powerpoint vibe at NASA. If their founder were anyone else, SpaceX’s incredible track record of achievement would force us to take their Mars plan[65] seriously. But their founder is who he is, and what he has publicly shared is not so much a blueprint as an inspirational poster. Musk’s vision for the company hinges on a reusable rocket called Starship, which will be able to do everything—refuel in space, re-enter either the Martian or Earth atmosphere, land on the Moon, make an amazing cup of coffee. Economies of scale will make this rocket so cheap that it will soon cost less to launch things into space than to keep them on Earth. At that point, moving to Mars will just be a matter of buying a second-hand Starship and filling it with Monster energy drinks and oxygen. The difficult and unglamorous problems of a Mars mission—how do you wash your socks? What is there to eat?— get no love from Elon. Once you get beyond “rocket factory go brrrrr,” there is no plan, just a familiar fog of Musky woo. The Mars rockets will refuel from autonomous robot factories powered by sunlight. Their crews will be shielded from radiation by some form of electromagnetic handwaving. Life support, the hardest practical problem in space travel, “is actually quite easy”. And of course Musk dismisses the problem of microbial contamination (which I can’t emphasize enough is governed by international treaty) as both inevitable and no big deal. But SpaceX is ultimately in the business of building rockets, not zoo enclosures. And as any Tesla owner can attest, slowly working the bugs out of a life-critical technology is not what keeps the world’s most distractible CEO entertained. In the end there are just two organizations (Roscosmos and NASA) that have deep enough expertise in life support to make it work on Mars-length missions. SpaceX will either have to find a way to work with them, or hire away[66] their experts. If you have faith in Musk, there’s nothing I can say to shake it. But if you notice a pattern in his past promises—the hypertunnel that is just a regular tunnel, the door panels that fall off the self-driving car, the robot that’s only a guy in a suit—then maybe you’ll be persuaded that firing difficult problems into space does not make them easier, and that the challenges I’ll lay out here will apply no matter whose name is on the rocket. Wherever you stand on the matter, whether you’re a Musk fanboy, an unaligned Mars obsessive, or just biplanetary/curious, I invite you to come imagine with me what it would take, and what it would really mean, for people to go put their footprints in the Martian sand. Next week: The Shape of a Mars Mission Footnotes [1] I’ll justify this figure in detail later on. For now, consider that each SLS launch costs $4.2B, and that developing just the Orion space capsule has cost $20B. The ISS, which is functionally close to a Mars transfer vehicle, has so far cost $250 billion. [2] This is the date you get when you add the minimum time required for research, design, and testing to the earliest date we're likely to have a working lunar base (which is needed to start the research bit). I'll talk about it in detail later. [3] John Young commanded the first Space Shuttle flight; the context of the original quote was his assessment of a particularly exciting Shuttle abort mode called ‘Return To Landing Site’. [4] For orbital mechanics reasons, Mars launch windows are 26 months apart. We'll talk about this in Section 1. [5] For example, early space station designs circa 1969 assumed a crew of 50-100 men working in geosynchronous orbit. Many of the early Space Shuttle astronauts were refugees from an Air Force program called the Manned Orbiting Laboratory, a kind of inhabitable spy satellite that the Air Force came very close to launching in the early 1970's. For a representative Skylab-era view, see Weitz, The Role of Man in Conducting Earth Resources Observations From Space, doi.org/10.2514/6.1974-250 [6] For example, Mariner 4 (1965) photos were 240,000 bits in size; the orbiter sent them back at 8.5 bits per second. The HiRISE camera on the Mars Reconnaissance Orbiter (2005), source of most of the photographs in this essay, takes 28 Gibit photos that are sent to Earth at up to 4 Mbps. [7] I know, no robot can reflect on the nature of the Sublime while looking at sunbeams dancing on the limb of Deimos or whatever. But when it comes to tasks like “look under this rock on Mars” or “fly through this plume and sample it”, robots are awesome. [8] For example, compare the $93 billion spent on Artemis through 2025 with the $435 million program cost of the VIPER lunar rover, or the $264 billion estimated cost of a Mars landing in “Evaluation of a Human Mission to Mars by 2033 ” compared to $3.5 billion for the Mars Science Laboratory and Curiosity rover. (Figures in 2022 dollars) [9] Apollo 17 took off from the Moon on December 14, 1972. This was the last time human beings ventured beyond low earth orbit. [10] NASA gave the total cost of ISS as $150B in 2010; adjusting this figure for inflation and adding 12 years of operating costs (at about $3 billion/year) adds up to almost exactly a quarter trillion dollars. [11] Some of the notable discoveries made by spacecraft after 2000: Kepler finds over 2,600 exoplanets Curiosity discovers that Mars was habitable Hubble telescope discovers galaxies at high redshift (z > 8) Cassini observes water jets and organic molecules on Enceladus Huygens lands on Titan Mars Express discovers subsurface lakes on Mars WMAP and Planck measure the cosmic background radiation to high precision. New Horizons flies by Pluto Dawn finds water on Vesta Rosetta gives us our first close look at a comet Gaia maps the Milky Way Compare this to NASA’s official list of ISS breakthroughs, which include “monitoring our planet from a unique perspective”, “student access to an orbiting laboratory”, and “responding to natural disasters”. [12] The first segment of the ISS launched in 1998; I’m counting from the arrival of the first permanent crew in November 2000. [13] This result has been very controversial, since the surrounding rock should be far too cold even for supercooled brine to exist as a liquid. The counterargument is that the bright radar reflections must be geological features, not water. However, recent evidence finds independent support for the subglacial lake theory. This is one of those unhappy situations where you can’t just rely on Wikipedia, but have to go read the papers, like an animal. See: (i) Lauro, S.E., Pettinelli, E., Caprarelli, G. et al. Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data. Nat Astron 5, 63–70 (2021). doi.org/10.1038/s41550-020-1200-6 (ii) Lauro, S.E., Pettinelli, E., Caprarelli, G. )et al. Using MARSIS signal attenuation to assess the presence of South Polar Layered Deposit subglacial brines. Nat Commun 13, 5686 (2022). doi.org/10.1038/s41467-022-33389-4 (iii) Arnold, N.S., Butcher, F.E.G., Conway, S.J. et al. Surface topographic impact of subglacial water beneath the south polar ice cap of Mars. Nat Astron 6, 1256–1262 (2022). doi.org/10.1038/s41550-022-01782-0 [14] For a discussion of this and a possible heating mechanism, see Sori, M. M., & Bramson, A. M. (2019). Water on Mars, with a grain of salt: Local heat anomalies are required for basal melting of ice at the south pole today. Geophysical Research Letters, 46, 1222– 1231. doi.org/10.1029/2018GL080985 [15] Broquet, A., Andrews-Hanna, J.C. Geophysical evidence for an active mantle plume underneath Elysium Planitia on Mars. Nat Astron (2022). doi.org/10.1038/s41550-022-01836-3 [16] Baucon, Andrea, Carlos Neto De Carvalho, Fabrizio Felletti, and Roberto Cabella. 2020. "Ichnofossils, Cracks or Crystals? A Test for Biogenicity of Stick-Like Structures from Vera Rubin Ridge, Mars" Geosciences 10, no. 2: 39. doi.org/10.3390/geosciences10020039 [17] E.B. Rampe, D.F. Blake, et al. Mineralogy and geochemistry of sedimentary rocks and eolian sediments in Gale crater, Mars: A review after six Earth years of exploration with Curiosity, Geochemistry, Volume 80, Issue 2, 2020. doi.org/10.1016/j.chemer.2020.125605. [18] As who among us has not! See: Moores, J. E., King, P. L., Smith, C. L., Martinez, G. M., Newman, C. E., Guzewich, S. D., et al. (2019). The methane diurnal variation and microseepage flux at Gale crater, Mars as constrained by the ExoMars Trace Gas Orbiter and Curiosity observations. Geophysical Research Letters, 46, 9430– 9438. doi.org/10.1029/2019GL083800 [19] Chun, Jongsik, Rainey, Fred A., Integrating genomics into the taxonomy and systematics of the Bacteria and Archaea. International Journal of Systematic and Evolutionary Microbiology, VO 64. doi.org/10.1099/ijs.0.054171-0 [20] Kennedy, A.C., Smith, K.L. Soil microbial diversity and the sustainability of agricultural soils. Plant Soil 170, 75–86 (1995). doi.org/10.1007/BF02183056 gives a figure of 87% undiscovered, citing Hawksworth 1991 [21] Estimates of total microbial biodiversity depend on a raft of modeling assumptions, and there is an ongoing debate about whose model is more realistic. Note that the one trillion figure is not an upper bound. See Lennon and Locey, Scaling Laws Predict Global Microbial Diversity (2016) doi.org/10.1073/pnas.1521291113 and More support for Earth’s Massive Microbiome (2020) doi.org/10.1186/s13062-020-00261-8 for a discussion. [22] Discovering a phylum is a big deal; imagine suddenly noticing the existence of vertebrates, or flowering plants. The microbial revolution in the early 21st century found something like 30 new phyla; scientists expect to find 1,300 more. (source: Yarza, P., Yilmaz, P., Pruesse, E. et al. Uniting the classification of cultured and uncultured bacteria and archaea using 16S rRNA gene sequences. Nat Rev Microbiol 12, 635–645 (2014). doi.org/10.1038/nrmicro3330) [23] Specifically, a type of archaea called DPANN and the “Candidate Phyla Radiation” in bacteria. DPANN organisms were hard to discover since they are almost exclusively symbiotic; their past may shed light on the evolution of eukaryotes. See Cindy J. Castelle, Jillian F. Banfield, Major New Microbial Groups Expand Diversity and Alter our Understanding of the Tree of Life, Cell, Volume 172, Issue 6, 2018, Pages 1181-1197, ISSN 0092-8674. doi.org/10.1016/j.cell.2018.02.016. [24] Morono, Y., Ito, M., Hoshino, T. et al. Aerobic microbial life persists in oxic marine sediment as old as 101.5 million years. Nat Commun 11, 3626 (2020). doi.org/10.1038/s41467-020-17330-1 [25] Bengtson, S., Ivarsson, M., Astolfo, A., Belivanova, V., Broman, C., Marone, F. and Stampanoni, M. (2014), Deep-biosphere consortium of fungi and prokaryotes in Eocene subseafloor basalts. Geobiology, 12: 489-496. doi.org/10.1111/gbi.12100 [26] Like everything to do with the deep biosphere, estimates on biomass differ by a couple of orders of magnitude. [27] Yarza, P., Yilmaz, P., Pruesse, E. et al. Uniting the classification of cultured and uncultured bacteria and archaea using 16S rRNA gene sequences. Nat Rev Microbiol 12, 635–645 (2014). doi.org/10.1038/nrmicro3330 [28] Tina Šantl Temkiv, Kai Finster, Bjarne Munk Hansen, Niels Woetmann Nielsen, Ulrich Gosewinkel Karlson, The microbial diversity of a storm cloud as assessed by hailstones, FEMS Microbiology Ecology, Volume 81, Issue 3, September 2012, Pages 684–695, doi.org/10.1111/j.1574-6941.2012.01402.x [29] Petit, Pauline C. M., Olivier Pible, Valérie Van Eesbeeck, Claude Alban, Gérard Steinmetz, Mohamed Mysara, Pieter Monsieurs, Jean Armengaud, and Corinne Rivasseau. 2020. "Direct Meta-Analyses Reveal Unexpected Microbial Life in the Highly Radioactive Water of an Operating Nuclear Reactor Core" Microorganisms 8, no. 12: 1857. doi.org/10.3390/microorganisms8121857 [30] DasSarma, Priya, André Antunes, Marta Filipa Simões, and Shiladitya DasSarma. 2020. "Earth's Stratosphere and Microbial Life" Current Issues in Molecular Biology 38, no. 1: 197-244. doi.org/10.21775/cimb.038.197 [31] Daisuke Fujiwara, Yuko Kawaguchi, Iori Kinoshita, Jun Yatabe, Issay Narumi, Hirofumi Hashimoto, Shin-ichi Yokobori, and Akihiko Yamagishi. Mutation Analysis of the rpoB Gene in the Radiation-Resistant Bacterium Deinococcus radiodurans R1 Exposed to Space during the Tanpopo Experiment at the International Space Station. Astrobiology. Dec 2021.1494-1504.doi.org/10.1089/ast.2020.2424 [32] Steinle, L., Knittel, K., Felber, N. et al. Life on the edge: active microbial communities in the Kryos MgCl2-brine basin at very low water activity. ISME J 12, 1414–1426 (2018). doi.org/10.1038/s41396-018-0107-z [33] Vreeland, R., Rosenzweig, W. & Powers, D. Isolation of a 250 million-year-old halotolerant bacterium from a primary salt crystal. Nature 407, 897–900 (2000). doi.org/10.1038/35038060 [34] For viable microbes found in 8 milion year old ice, see “Fossil genes and microbes in the oldest ice on Earth doi.org/10.1073/pnas.0702196104 [35] Fang J, Kato C, Runko GM, Nogi Y, Hori T, Li J, Morono Y and Inagaki F (2017) Predominance of Viable Spore-Forming Piezophilic Bacteria in High-Pressure Enrichment Cultures from ~1.5 to 2.4 km-Deep Coal-Bearing Sediments below the Ocean Floor. Front. Microbiol. 8:137. doi.org/10.3389/fmicb.2017.00137 [36] See discussion in: Nicholson, W.L. (2020). Spore-Forming Bacteria as Model Organisms for Studies in Astrobiology. In Extremophiles as Astrobiological Models (eds J. Seckbach and H. Stan-Lotter). doi.org/10.1002/9781119593096.ch13 [37] Full video is at https://www.c-span.org/video/?522488-1/nasa-holds-briefing-moon-mars-program [38] Obama originally directed NASA to land by 2033; Nelson said that the earliest a Mars landing can happen now is in the late 2030’s or early 2040’s. [39] Not a typo; the total budget for ocean exploration is about half of what NASA plans to spend next year ($48.3 M) on architecture studies for Mars. [40] Here are the reasons a “Why Mars?” conference came up with in 1992: Human Evolution- Mars is the next logical step in the expansion of the human race into the stars. Comparative Planetology- by understanding Mars and its evolution as a planet, a better understanding of Earth will be achieved. International Cooperation- an international Mars exploration effort has the potential to bring about a sense of global unity as never seen before. Technological Advancement- the development of new and improved technologies for the Mars mission will enhance the lives of those on Earth while encouraging high-tech Inspiration- the human Mars exploration mission will test our technological abilities to their maximum. The ingenuity of the mobilized populace will be tested and our accomplishments will serve to inspire future generations. A common focus will unite people from around the world as they expand the envelope of achievability. Investment- the cost of a crewed Mars exploration mission is reasonable when compared with the costs of other current societal expenditures. Note that only the first two of these reasons have any connection to Mars, and even back in 1992, ‘Comparative Planetology’ was best done by space probe. The others are all riffs on “doing difficult things together builds character”, while (6) is just kind of plaintive. Fourth graders writing to Santa make a stronger case for an X-Box than NASA has been able to put together for a Mars landing. [41] In 2022, NASA spent $6.79B on Exploration (Moon-to-Mars stuff) and $4.04B on Space Operations (running the ISS). I lump the two together since ISS research is almost entirely in support of life support for the Moon-to-Mars mission. Source: https://www.planetary.org/space-policy/nasas-fy-2022-budget [42] The National Science Foundation budget was $8.8 billion in 2022. [43] More precisely, outside Earth’s magnetosphere, which blocks a large fraction of the radiation that we need to study. [44] The key question is whether Martian gravity (0.38g) is enough to stop the kinds of degenerative processes we see in freefall. We’ll talk about this in detail in the section on deconditioning. [45] The best guess right now is that a 40 year old woman would face between a 3% and 21% risk of dying from cumulative radiation exposure on a 940 day Mars mission (at 95% confidence). The large uncertainty comes from lack of data on the effects of heavy ion radiation. See Francis A. Cucinotta, Eliedonna Cacao, Myung-Hee Y. Kim, Premkumar B. Saganti, Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations, Acta Astronautica, Volume 166, 2020. doi.org/10.1016/j.actaastro.2018.08.022. [46] I’ll talk about why it’s impractical to build a rotating spacecraft for this purpose in the section on artificial gravity. [47] Trump actually made this offer to NASA, who sensibly refused. [48] There’s no a priori reason a Mars mission has to have closed-loop life support, but NASA treats it as a requirement. As a practical matter, you do have to at least recycle water. I’ll discuss open/closed loop tradeoffs in detail in the section on life support. [49] The current mass of ECLSS components on the ISS is 1,776 kg (source: ICES-2021-212, An Environmental Control and Life Support System (ECLSS) for Deep Space and Commercial Habitats), with an estimated cost of development of $200 million, giving $110,000 per kilogram. At this writing, the price of gold was $58,000 per kilogram. [50] I’ll talk about the four basic mission types later. Here I’m assuming a long-stay surface mission, but the argument holds for any of them. [51] One way to make the problem not matter is to contaminate Mars early and often, which makes Musk’s plan to land cargo on the surface in bulk as soon as possible particularly cynical. [52] No mission has searched for life on Mars since the original Viking landers (which I’m calling Step 0). [53] The Viking landers were the cleanest objects ever sent to Mars; subsequent landers and rovers have received more of a quick wipedown. I’ll talk about the complex standards that govern this in the section on contamination. For a good rant on the qualitative difference between robots and human crews, see Alberto G. Fairén, Victor Parro, Dirk Schulze-Makuch, and Lyle Whyte. “Searching for Life on Mars before it is too late” Astrobiology. Oct 2017. 962-970. doi.org/10.1089/ast.2017.1703 [54] I’ll talk about why microbial communities are vastly more adaptive than singletons in the section on microbes. [55] The requirement to avoid contamination is a clause in the 1967 Outer Space Treaty. The detailed guidelines for what this means are formulated by an international body called COSPAR. I'll go over these rules in gripping detail in the section on contamination. [56] For a taste of how restrictive an explorer's life would be, see Bobskill, Marianne, and Mark L. Lupisella. "Human Mars Mission Surface Science Operations." In SpaceOps 2014 Conference, p. 1620. 2014. https://doi.org/10.2514/6.2014-1620 [57] See NASA’s Management of the Artemis Missions, Office of Inspector General (IG-22-003) [58] As a rough rule of thumb, a probe to explore a planetary system costs $5 billion, while a smaller mission costs $1 billion. This does not factor in economies of scale from building and launching a number of probes at once, since we’ve never had the money to do that. [59] The moons with liquid water are Ganymede, Europa, Callisto and Enceladus, with a recent surprise fifth contender, Mimas, the little moon that looks like a Death Star. [60] Voyager 2 flew by Uranus in 1986 and Neptune in 1988, and that’s the last we saw of them. [61] NASA plans to de-orbit the ISS in 2031, but Roscosmos says they’ll bail in 2024. [62] I base this figure on the 2023 NASA budget request, which earmarks $7.4 billion for Moon-to-Mars stuff and $4.2 billion for the ISS. [63] For context, consider the cost of missions like Europa Clipper ($5 billion), the Mars Science Laboratory / Curiosity Mars rover ($3.2 billion), or the Roman Space Telescope ($3.2 billion). There is potential for substantial savings by binning similar missions, sharing hardware, and not being forced to launch on NASA’s overpriced rockets. [64] No one seems to want to go to Venus, but conditions higher up in the atmosphere are surprisingly mild (0.53 bar, 27C at ~55km). If not for the sulfuric acid, astronauts could even go relax outside their blimp wearing just shorts and an oxygen mask. For a cool blimp mission to Venus, see: https://ntrs.nasa.gov/citations/20160006329 [65] I’m assuming the adults who run SpaceX have a more realistic plan for Mars that they kept hidden away from Musk, in a room he doesn’t know exists. Here I’m only talking about Musk’s version. [66] I would pay large sums of American money to be a fly on the wall at the meeting where someone tries to pitch senior career civil servants on working for Elon Musk.

Part of what brought me to Taiwan was bureaucratic thrill seeking. Few other countries had gone from “just hop on a plane” to North Korean levels of inaccessibility as fast as Taiwan, and like a cat that paws at a door just because it's closed, I wanted in. The country was off-limits to foreign visitors, but there was a tiny gap left in the regulations, and with the right references, statements of purpose, and forms filled out in triplicate it might just be possible to get a Taiwan visa and come eat all the noodles. It was not easy! Even buying the plane ticket felt like an LSAT word problem. I could only arrive during a certain window of time on a weekday, and I had to send my visa number eight business days in advance (minding the international date line) in order to secure an entry permit that would be emailed to me after my flight took off. I would have to take a PCR test no earlier than 48 hours before landing, but at least 12 hours before departure. I needed proof of travel to get the visa, and a visa to book the plane ticket. One gate agent always lied, while another only told the truth. It wasn’t until they let me on the plane that I believed this might actually work. It had been two years since my last international flight, and the feeling of stepping back in time was intense. Our domestic airlines might have covid fatigue, but for China Airlines it was still April 2020. The poor flight attendants had to wear latex gloves, goggles, face shield, and a full-body plastic gown on top of their regular uniform for the entire thirteen hour flight. The hazmat team that met our flight in Taipei made the flight attendants look reckless. A dozen or so staff in bunny suits put numbered stickers on our shoulders and read off names ten at a time. It took maybe twenty minutes to give everyone a PCR test, and another forty to get the result. When a lab worker finally came in to give us the all-clear, everybody cheered. On our way out, I was given a little plastic card attesting that our flight was at low risk for African swine fever, the other disease Taiwan is trying to keep out of its borders. Then I saw a young woman holding up my name on a sign. The Ministry of Education had sent her to shepherd me through the arrival procedure; she had spent the night in the terminal in order to meet the early flight. Her name tag said “Angel”. I had been briefed about what to do on arrival, but in airport situations I am an agent of chaos and the Taiwan government was wise not to take chances. The first task was to get a local SIM card so the Central Epidemic Command Center could keep track of me. I was cautioned not to turn my phone off and to answer any phone calls promptly, in order to avoid an awkward visit from the police. Next we walked into an open space that looked like a Mad Men episode filmed at Chernobyl. There was a grid of large desks, and a bunny-suited pandemic worker was seated behind each one. A woman called me over to her desk and made me photograph a little calendar. Then she handed me a box of covid self-tests, and mimed that was supposed to take them on the days marked in red. In exchange for the tests they asked me for the swine fever card, which I had misplaced the second I got it. By now I was carrying my luggage, entry card, phone, documents, passport, box of tests, and a tiny plastic baggie with my old SIM card inside it. Every time we stopped I found a way to lose a different combination of these items, and my poor guide lived up to her English name as she watched me rummage through my bag every ten feet. The other passengers were long gone. The Taipei airport is one of those massive hubs set up to handle thousands of arrivals at once, but when we made it to passport control, it was deserted except for a single booth at the far corner. It felt just like leaving the Tokyo airport in May 2020, an enormous building with nobody in it. The main terminal was also empty except for the police, the first people I had seen who were not wearing full-body protective gear. Some of the ribbons were bright red, and the cops motioned to us to disconnect them and step through the red zones until we reached the exit. My feeling of being a dangerous pathogen breaking through the island’s defenses intensified. At the taxi rank, a final set of bunny-suited workers sprayed everyone's luggage and body with disinfectant, not forgetting the soles of the feet. My name was checked off a list and they hustled me into a quarantine cab, where a wall of plastic sheeting had been set up to protect the cab driver. It was a true Tom Friedman moment. This half-hour journey into Taipei would be my only glimpse of Taiwan for the next ten days, so whatever insights I had about this place, I’d better have them quick. Instead, my phone buzzed, reminding me to call my quarantine hotel and warn them I was coming in hot. The staff at the hotel had prepared a plastic chute to funnel guests in from the street through the lobby and into a dedicated “red” elevator. When the cab pulled up, the desk clerk slid some documents at me through a gap in the plastic, showed me how to add the hotel as a contact in LINE (Taiwan’s universal chat app) and then sent me upstairs to start doing time. If The Shining had been shot on a budget, the Santos Hotel would have been a good choice for a set. The hallways were dark and silent; the single plastic-wrapped chair in front of each door gave the place an eerie feeling. Later I realized the chair was just a place to put food trays. Inside my room I found a case of bottled water, a fork and chopsticks, and a brand new digital thermometer. Every surface that my virus-soaked fingers might touch, including the light switches, remote control, telephone, toilet handle, and thermostat, had been wrapped in protective plastic. As an avid indoorsman, I did not expect staying in one room for ten days to be difficult, but confinement left me feeling surprisingly antsy. At the same time, Taiwan was the first time in two years I had experienced pandemic competence. The feeling was so unusual and refreshing that I never begrudged the fuss they made. The fact that my quarantine coincided with the debacle in Shanghai only deepened my sense of gratitude. For its part, the hotel took good care of us. The water was hot and the internet was fast. Lunch and dinner were bento boxes with Chinese characteristics. Breakfast was a wild card—one morning they gave me what I swear was a churro sandwich. The hotel also let guests order in. Back in America, I had spent sleepless nights regretting all the noodles that were going uneaten by me across East Asia. Now I was locked in a room with nothing to do except order from Taipei's extensive delivery network. Soon mopeds from every quarter of the city were converging on the Santos Hotel, and the poor chair outside my door groaned under a pyramid of dinners. Nobody will ever care about my health the way they did in that hotel. Every morning brought an automated call from the CECC, asking me to press one if I had survived the night. “The Central Epidemic Command Center cares about you,” the voice would remind me, and I believed it! If I got sick, I had no doubt I’d be taken someplace safe where people would take care of me, more reassurance than I had ever had back in America. Twice a day I had to report my temperature to the hotel, as well as deny a long list of symptoms on a Google form. And in the early afternoons, my visa sponsor would call in to check in on me. Every third day I had to take one of the rapid tests from the airport. The instructions were a wall of Chinese, but a set of IKEA-like drawings made things clear enough. The box of tests even had a little hole to hold the test vial, and the procedure reminded me of celebrating Mass. I would sit in front of the little vial stirring and muttering “hoc est mucus meum,” then apply three drops to the test wafer and pray for good health. On the last day of quarantine we had to pass another PCR test. This was administered in a converted city bus that roved between the several quarantine hotels; like the Second Coming, no man knew its appointed hour. The hotel told us to be ready on ten minutes’ notice, and throughout the hotel excited guests sat by their doors, wearing pants for the first time in ten days, hungry for a glimpse of the sky. When the bus came, I did my best to linger, but the trio of bunny-suited health workers was too efficient. One checked my name on a clipboard while a second rubbed the back of my brain with a test swab, and before I could stall I was being shooed back into the plastic chute. They say you only do two days in quarantine—the day you arrive and the day you leave. My bus test must have been negative, because the next morning the hotel had put me out on the street, upgraded to a ghostly status called “self-health monitoring”. I could move into my real apartment, and even walk the streets of Taipei, but for seven days I was barred from crowded places or public transit. Once I was free to actually see the city, the sense of traveling back in time intensified. Everyone in Taipei wore a face mask, even people on remote hiking trails. Temperature checks and hand sanitizer were unavoidable. Every building and storefront had a QR code posted at the entrance for contact tracing, and people took care to scan it and text the central authority before going inside. Woe unto those who forgot their cell phone! On the evening news, I could see whole teams of hazmat-suited workers fumigating the subway system and outdoor sidewalks, just like back in that first pandemic spring. All told, it took seventeen days, three PCR tests, and five rapid tests for me to become street legal in Taiwan. Sadly, my quarantine period ended just as a wave of infections was beginning to break through the island's defenses. At this point the virus has simply become too infectious. After two years of successful eradication, the country will have to make the transition to living with covid like the rest of us. As I write this, the public health authority is trying to walk a delicate balancing act between getting everyone vaccinated and normalizing a disease that people have been treating like the black plague. For me, this brief quarantine in Taiwan was a glimpse into an alternate reality where pandemic response was not a shitshow. People knew what they were doing, there was a plan and adequate resources to make it work, and everyone seemed to be living in a shared reality when it came to fighting an infectious disease. Even though I was a foreigner and a potential vector for the pandemic they were trying to keep out of their country, at every step I was treated with kindness and respect. I don't think I could explain to anyone in Taiwan how novel this feeling is to an American, but I will always be grateful to them for it, and for the lengths they went to keep foreign guests like me safe while I plundered their restaurants. I hope the public health system can continue to lead by example as this next, difficult stage of the pandemic begins. And I hope someday we have something like it back home.