Tuesday, December 26, 2023

There Is No Planet B: Part 2

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In Part 1 I applied basic arithmetic to the logistics of Elon Musk's claimed plans for colonizing Mars in 2050 to show they were implausible. Below the fold I continue, first by discussing Maciej Cegłowski's equally basic dissection of NASA's economically implausible plans for Mars in Why Not Mars?. Second, by reviewing the host of non-logistical and non-economic problems facing humans attempting to survive on Mars based on:


There are two known programs planning to land humans on Mars, Musk's and NASA's. Cegłowski's massively footnoted (which I omit) post starts by asking the obvious question of each "What are they trying to achieve?":
  • Musk's is the establishment of a backup planet for humans in case the primary fails. Cegłowski writes:
    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.
    The best that can be said for this is that it is "aspirational", many orders of magnitude more aspirational than, for example, the idea of autonomous Tesla robotaxis earning while their owners sleep.
  • NASA's primary goal is much less aspirational; it appears to be to use the idea of "one small step for a man" on Mars to ensure the continuation of the manned space-flight program. Cegłowski is scathing about NASA's inability to articulate a rational justification, quoting NASA administrator Bill Nelson:
    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.
    The destiny that is being fulfilled here is NASA's manned space-flight program, which has conspicuously failed to deliver "new things ... to improve ... our lives here on earth". The things that have improved lives, from weather forecasts, satellite communications, earth observation and so on have all come from the unmanned side of NASA. As have all the scientific discoveries from astronomical missions such as Hubble and James Webb, and of greater relevance here, planetary missions such as Opportunity and Perseverance. Note how Nelson elides the difference.
If NASA's justification for landing on Mars is science, helping to answer the Ultimate Question of Life, the Universe and Everything by discovering life there, there are three big problems:
  • Economics: using humans increases the cost by at least a couple of orders of magnitude.
  • Schedule: using humans delays results by at least a couple of decades.
  • Science: using humans inevitably contaminates Mars with Earth lifeforms, rendering a definite answer to the research questiuon impossible.
Cegłowski points out that the last couple of decades have seen a vast expansion of understanding of life on Earth:
Microbiologists had long suspected that the 12,000 or so known species of microbes were just a fraction of the total, with perhaps another hundred thousand “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. In the genomic gold rush that followed, researchers discovered not just dozens of unsuspected microbial phyla, but two entire new branches of life.

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].
And that what this means for the search for life on Mars is critical:
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.
Cegłowski points out that NASA has to care about contaminating Mars:
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.
Musk's likely attitude to this treaty can be inferred from the title of Douglas Rushkoff's ‘We will coup whoever we want!’: the unbearable hubris of Musk and the billionaire tech bros.

Cegłowski has noticed NASA manned spaceflight's track record:
Sticking a flag in the Martian dust would cost something north of half a trillion dollars, with no realistic prospect of landing before 2050. 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”. 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.
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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, 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.
Members of the cult of Musk will ignore the elephant in the room, which is life support, but NASA cannot:
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.

In particular, we need preliminary data on the physiological effects of partial gravity, and a better estimate of the risk from heavy ion radiation. Since core tradeoffs around crew safety depend on the outcome, these experiments have to be done before NASA can finalize a mission design.
But partial gravity and radiation aren't the big life support problem:
The chief technical obstacle to a Mars landing is not propulsion, but a lack of reliable closed-loop life support. 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 and there is little appetite for it here on Earth, where plants do a better job for free.
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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.
NASA's requirement is for a completely closed-loop life support system capable of keeping say 6 people healthy for at least 30 months. This is way beyond the state of the art. Musk's is for a similar system capable of keeping a million people healthy indefinitely.

There isn't a good justification for sending humans to Mars, and the technology for doing it doesn't exist yet. Even assuming the bill was only $500B in 2023 dollars, the idea that Congress would consistently fund $20B every year for a program that wouldn't produce its headline result for two-and-a-half decades fails the laugh test. Implausible is a polite way to describe the economics of NASA's plan.

Lets suspend disbelief and assume some humans do land on Mars. Two popular works of hard science fiction about Mars that are fairly plausible about logistics both ignore some of the known problems:
  • Andy Weir's The Martian ignores two big problems. First, Mark Watney spends 549 sols (564 days) on the Martian surface plus the outbound and return trips, for a total of say 1000 days radiation exposure with no shielding. Second, he survives by eating potatoes grown in a mixture of Martian soil and human excrement.
  • Kim Stanley Robinson's Martian Trilogy describes how Mars is terraformed, including providing it with a breathable atmosphere. He doesn't describe how the atmosphere is prevented from leaking back into space.
Problem 1: The collapse of Mars' magnetic field caused it to lose its primordial atmosphere. Without a magnetic field, the same processes would require the terraformed atmosphere to be continually resupplied from elsewhere. Providing Mars with a magnetic field is an interesting engineering problem.

Problem 2: Radiation environment for future human exploration on the surface of Mars: the current understanding based on MSL/RAD dose measurements by Jingnan Guo et al states:
The accumulated GCR dose equivalent, via a Hohmann transfer, is about 0.65±0.24 sievert and 1.59±0.12 sievert during solar maximum and minimum periods, respectively.
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A typical round-trip mission scenario to Mars using a Hohmann transfer trajectory both ways thus includes about 400–500 days of transit time and 500 days of surface stay.
A 1 sievert dose:
In a short term dose is about the threshold for causing immediate radiation sickness in a person of average physical attributes, but would be unlikely to cause death. Above 1000 mSv, severity of illness increases with dose. If doses greater than 1000 mSv occur over a long period they are less likely to have early health effects but they create a definite risk that cancer will develop many years later.
Lets say the radiation dose for the emigrants is around 0.75 sieverts/year. 0.02 sieverts/year:
Averaged over 5 years is the limit for radiological personnel such as employees in the nuclear industry, uranium or mineral sands miners and hospital workers (who are all closely monitored).
So the emigrants are subject to 36 times the radiation level considered safe for persons subjected to radiation in their jobs. Watney would likely get cancer. Robinson acknowledges but underplays the radiation issue.

Problem 3: Plants grown in Martian soil will take up perchlorates:
"Anybody who is saying they want to go live on the surface of Mars better think about the interaction of perchlorate with the human body," he warned. "At one-half percent, that's a huge amount. Very small amounts are considered toxic. So you'd better have a plan to deal with the poisons on the surface."

Any humans exploring Mars, Smith said, will find it hard to avoid the finest of dust particles. "It'll get into everything…certainly into your habitat."
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The research emphasizes that perchlorate is widespread in Martian soils at concentrations of between 0.5 to 1 percent. There are dual implications of calcium perchlorate on Mars. On one hand, at such concentrations, perchlorate could be an important source of oxygen. But it could also become a critical chemical hazard to astronauts.
Perchlorates aren't just toxic, but also:
Perchlorate is highly soluble in water, and relatively stable and mobile in surface and subsurface aqueous systems.
Watney would have been poisoned both by his potatoes and by breathing the Martian dust. So would Robinson's Martians, who would also be poisoned by the Martian water.

The implications of the toxicity of the Martian dust for human exploration are so awkward that the response seems to be "ignore it and hope it goes away". For example Mars Needs Insects by Sarah Scoles in the NYT is about the virtues of soldier fly larvae for growing plants in Martian regolith. It is based on research using simulated Martian regolith from a company called Martian Garden that doesn't contain perchlorates. Presumably this is because its toxicity would severely limit the potential market.

But toxicity isn't the only problem posed by Martian dust. It is a real problem for solar power:
Mars’ dust storms aren’t totally innocuous, however. Individual dust particles on Mars are very small and slightly electrostatic, so they stick to the surfaces they contact like Styrofoam packing peanuts.

“If you’ve seen pictures of Curiosity after driving, it’s just filthy,” Smith said. “The dust coats everything and it’s gritty; it gets into mechanical things that move, like gears.”

The possibility of dust settling on and in machinery is a challenge for engineers designing equipment for Mars.

This dust is an especially big problem for solar panels. Even dust devils of only a few feet across — which are much smaller than traditional storms — can move enough dust to cover the equipment and decrease the amount of sunlight hitting the panels. Less sunlight means less energy created.

In “The Martian,” Watney spends part of every day sweeping dust off his solar panels to ensure maximum efficiency, which could represent a real challenge faced by future astronauts on Mars.
This alone likely makes solar power impractical for powering human habitation on Mars. But there's an even worse problem; every few years Mars is completely covered in a dust storm that lasts months:
“Once every three Mars years (about 5 ½ Earth years), on average, normal storms grow into planet-encircling dust storms, and we usually call those ‘global dust storms’ to distinguish them,” Smith said.
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Global storms can also present a secondary issue, throwing enough dust into the atmosphere to reduce sunlight reaching the surface of Mars.
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Large global dust storms put enough dust in the air to completely cover the planet and block out the sun, but doing so ultimately dooms the storm itself. The radiative heat of sunlight reaching the surface of the planet is what drives these dust storms.
Source
This image is a:
Time-lapse composite of the Martian horizon as seen by the Opportunity rover over 30 Martian days; it shows how much sunlight the July 2007 dust storms blocked; Tau of 4.7 indicates 99% sunlight was blocked.
It is clearly uneconomic to over-provision solar panels by a factor of 100, even if they could be swept clear of dust. Nor is it practical to store enough power to last an unpredictable number of months while waiting out the storm. Nuclear reactors are the only feasible way to power human habitation on Mars, but putting tons of nuclear fuel on rockets that can fail and dump their contents in Earth's atmosphere isn't going to be popular. Let alone the chances of contaminating the Martian atmosphere when a reentry is misjudged.

These are far from the only known problems facing humans on Mars; there are bound to be many others, as yet unknown. Mitigating each of them will involve both difficult engineering and massive expense. All this for no clearly expressed benefit, and very clearly expressed negative scientific benefit. A far more practical and afforable policy would be to divert a small proportion of the funding from manned space-flight to a massive increase in automated exploration of the solar system and its plaents. And divert the rest to dealing with actual pressing problems on Earth, such as climate change.

1 comment:

Geoff said...

I nominate "Providing Mars with a magnetic field is an interesting engineering problem." as Understatement of the Year.