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Challenges to human spaceflight include the following:

  • radiation effects
  • psychological effects
  • management of resources for life support
  • muscle wastage

I know these are all major challenges to putting boots on Mars, but which is the most important to solve before we can make the first crewed Mars mission happen?

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  • $\begingroup$ Do the astronauts need to return to Earth or is it a one-way trip? $\endgroup$
    – Thorbjørn Ravn Andersen
    Commented 17 hours ago

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There is no technical barrier to a Apollo style Mars mission, and has not been since Skylab/Mir, with a well math'd Venus flyby proposed for 1973 that had answers for most of the points in the question.

The issue is this mission design is very much brute force - launch a large craft and then stuff it with several years worth of food for a very small (2-3 person) crew, that crew does as little as possible while in transit (reducing life support needs). If possible provide a lander so at Mars crew can plant a flag rather than just looking from orbit, then fly home.

The most costly/risky part of this mission is the lander, which is outside the human factors scope of the question.

The issue with the above mission profile is 'why'. It achieves a very expensive 'first' but otherwise is mostly about astronauts struggling with boredom and pooping in a bag which is hard to justify to taxpayers (and probably the crew).

An obvious improvement is to make life support more closed loop:

  • Lower launch mass/cost (in a way clearly explainable to the taxpayer)
  • Allows (and may even require) larger crew size (can bring actual geologists etc to Mars, rather than giving an astronaut a crash course)
  • Much more 'going on' both for crew and public interest
  • Design and possible even vehicle itself re-usable.
  • Lots more 'what do we do next' mission options.

Issue is that this makes mission much more complicated, and in particular there is three axis problem space of maximizing closed loop efficiency, reducing system mass and maximizing system reliability that while certainly solvable tends to produce decision paralysis in full system design in absence of firm mission scope and budget, while plenty of work has been done at subsystem level.

This means that should someone NEED to pull together a Mars mission 'by the end of the decade' most of the life support parts are already there, they just need to commit to choices and start iterating on hardware (ie spending money in large amounts).

So it could be argued the biggest obstacle is right combination of money and willingness to lock in a choice that is 'wrong' by at least one metric.

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    $\begingroup$ This answer could benefit from addressing the challenges the question mentions beyond resource management (i.e. radiation - commonly said to be a big / precluding problem, as well as psychology and muscle wastage). $\endgroup$
    – NotThatGuy
    Commented 20 hours ago
  • $\begingroup$ And even if you create a mostly closed loop system for as many consumables as possible you probably still need to ferry a large amount of consumables as a backup if parts of the closed loop systems fail. So while closed loop is preferable it probably won't reduce the launch mass by much. It's not like ISS where you can either ring the crew back almost anytime if necessary or resuply consumabes or replacement parts if something breaks. $\endgroup$
    – TrySCE2AUX
    Commented 5 hours ago
  • $\begingroup$ @TrySCE2AUX - see section at the end there about 'choice that will be wrong by at least one metric'. Mathing X supplies for Y people for Z days for an open loop mission is not hard project management. Doing a mission with partially closed loop means you either arrive back with very expensive supplies you did not need, or you had to send up the 'who to eat first' list. $\endgroup$
    – GremlinWranger
    Commented 5 hours ago
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Spoiler: Opinion based answer

I vote for “life support” as the most pressing question since it is an absolute necessity for astronauts making the round trip alive. Closed-loop life support has not been demonstrated.

Radiation will produce an increased probability of cataracts and cancer deaths after return, but would not prevent astronauts from returning.

Muscle and bone wasting could be crippling. There is also a risk of fatality during the mission due to kidney stones from hypercalcemia secondary to bone wasting.

Psychological stress would likely be handled by those steely eyed missile men. They got the right stuff.

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    $\begingroup$ You can probably upgrade things a bit from opinion based by referencing the long duration ISS missions as proving humans can survive 'plant flag and take a selfie' Mars mission like profiles just fine, concerns/research are more focused on feasibility or otherwise of living in space and/or Mars full time. $\endgroup$
    – GremlinWranger
    Commented yesterday
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    $\begingroup$ @KasieReam - the risks including radiation are well understood when it comes to 'can we get them back from Mars alive'. Issue is if the trip has long term chronic effects that are not considered acceptable. $\endgroup$
    – GremlinWranger
    Commented yesterday
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    $\begingroup$ But we have life support figured out. Sure, not closed-loop (or close to it) but the ISS has been running for quite a while and the support missions don't bring anything that couldn't be stashed at launch (or added in-orbit before transfer burns begin). Yes, it'll be almost absurdly heavy, but it's doable (if someone wants to waste the money) $\endgroup$
    – Hobbamok
    Commented yesterday
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    $\begingroup$ @KasieReam "Outside god knows how much radiation there is and what it will do to our brave astronauts. " no, we know pretty precisely as well $\endgroup$
    – Hobbamok
    Commented yesterday
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    $\begingroup$ @KasieReam if we use Hohmman Transfer windows, sure. Estimations for a realistic "faster" round trip are as low as 8 months total. But that's using a LOT more energy, so nuclear propulsion is a likely candidate. It COULD be done with conventional chemical propulsion and an unreasonable amount of money though haha. 3 years outside of the Earth's magnetic field would be quite spicy, and strapping a nuclear reactor to the vehicle might legitimately be a better overall. $\endgroup$
    – abestrange
    Commented 15 hours ago

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