Becoming an astronaut is notoriously difficult, with something on the order of 0.01% of all applicants getting picked for the job. To a large extent this is inevitable as only a dozen people per year will get to go to space, while hundreds of millions would potentially like to go. However there's also the component of skill and health - you can't go to space if you're 95 years old, if you have major health issues, if you're not intelligent enough to operate the controls and run the experiments, etc.

Did NASA or other space agencies ever publish estimates of what % of humans could realistically do an astronauts job if given the opportunity? I.e. if NASA was forced to pick the 5000th best candidate instead of the 1st best candidate, would they significantly lower the chance of a successful mission? What about the 50,000th best candidate? By "astronauts job" I'm referring to the most critical parts of the job, not just tagging along as a space tourist. In other words, what percentile of humans could staff the entire space mission without having to sacrifice anything in the process?

Since my previous question was misunderstood, here's an additional example to clarify what I'm thinking of:

  1. Imagine we're trying to replace every astronaut on the ISS
  2. We need to define what percentile of humans could do the job without harming the expected outcome of the mission (top 0.01%, top 1%, top 10%, etc)
  3. What would be the biggest percentile we choose within these constraints? In other words, what percentage of humans could do every single job carried out by ISS astronauts?

Assume that we're willing to provide a reasonable amount of training to the people applying - i.e. if someone isn't familiar with orbital mechanics but has the mental capacity to learn them, we're willing to spend time teaching them the gaps in their knowledge. If someone doesn't know how to operate lab equipment, we're likewise willing to spend a few months showing them the ropes.

  • $\begingroup$ "A reasonable amount of training" is really the key. It costs a lot of money to train astronauts, and they don't want to waste it on someone who won't stick around, will get sick, die, go on strike, get in disputes/fights with others, etc. So I think it's a lot less of CAN they do the job, and more of WILL they do the job. $\endgroup$ Commented Jul 6, 2022 at 17:55
  • $\begingroup$ @GregMiller there's different parts of the training though? Some of it happens long before the mission when astronauts go to college to study engineering/biochemistry/etc - I assume this type of training is relatively cheap. Some of it happens after you're picked for the job and that part is indeed expensive. $\endgroup$ Commented Jul 6, 2022 at 18:04
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    $\begingroup$ Yea, I assumed there are enough biologists, engineers, etc to be cheaply replaceable. The mission/astronaut specific training is still going to be very expensive. $\endgroup$ Commented Jul 6, 2022 at 19:02
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    $\begingroup$ I'm not the downvoter, but is there any actual data that could be used to answer this question? If not, it's opinion based. If all you are asking is, did NASA publish this number, the answer is no, because they don't know (or care) what the answer is either. They want to select people who can successfully do the job, not figure out some funky alternative means of picking the suboptimal candidates. Why would they? $\endgroup$ Commented Jul 6, 2022 at 23:51
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    $\begingroup$ @OrganicMarble There are no data that can be used to answer this question. The OP is asking for Controlled Unclassified Information (CUI) data. Leaking such data isn't quite as bad would be leaking classified information, but it can still spell fines and even perhaps years of free room and board for the leaker. (But rather substandard free room and board.) In other words, go directly to jail, do not pass go, do not collect $200. $\endgroup$ Commented Jul 8, 2022 at 0:48

1 Answer 1


The easy answer for replacing the crew of the ISS is that your process will 'pass' about as many as there are current Astronauts simple because you do not need that many and will just add filters until your candidate pool meets the number of spots even if the final criteria is number of vowels in their name or similar.

if we are looking at making random people astronauts we get to the question of risk. Currently there is a surplus of astronauts so they can be multi trained, so any of them can command a return to earth, take care of injuries or fix life support systems. If we relax that requirement, for example by making them all fly as 'spam in a can' to orbit with no manual control and then have an expert on the ground meat puppeting them via headphones and camera we get lots more candidates but increase our risks by hard to quantify amounts when things go wrong.

What we can do is look at things that would rule people out.

There are currently size restrictions borne of capsule size (cannot be big) and seating arrangements (cannot have short legs). These are engineering/cost problems that can be solved with money if there was a reason to do so. This is assuming the only space suit they get is a rescue ball.

These studies seem to suggest that the majority of vaguely healthy people can survive the G-forces of a ride to orbit, and out of a sample size of two even pacemakers will not rule people out.

Space sickness is a problem with the majority of people seeming to suffer from it to some extent, though it appears nobody who has flown has required a mission abort from it, though there is a self selection element here. There are probably a small number of people who would dehydrate or starve due nausea, assuming similar numbers to sea sickness that would be under 1%.

A more ambiguous criteria is psychological. Somewhere between 8 and 2% of the population are concerned enough by flying commercially to either not fly or medicate themselves to fly, approximately matching these numbers for a simulated flight in a centrifuge. given the claustrophobia etc of space flight the numbers should be expected to be higher. Noting the number that reported medicating via alcohol this may be a complication for astronaut selection - is it ok if they need to be drunk to get into the capsule?

In terms of the skills required, the majority of people who can afford to seek a private pilots license seem to pass the academic components given enough time, suggesting that most people when sufficiently motivated can learn a combination of new to them mechanical and theory skills to at least that extant. This also suggests the ability for most people to learn some non intuitive muscle memory survival skills (eg stall recovery) with enough practice and exposure.

This skill question is important, since as anybody who has taught someone to drive learns humans have a strong tendency to freeze when faced with complex decisions and while this is useful when say choosing the non poisonous fruit, in many hypothetical space situations freezing up is lethal. Training helps but there is a strong normal distribution to 'function under pressure' and the related avoidance of inattention blindness that current astronaut selection process gets to pick the top performers at and a more general selection system would just have to accept changes to design to 'idiot proof' things and accept that this design (eg removing manual overrides) and human nature would kill a hard to quantify number of people.

In terms of surviving the environment of cramped living conditions, limited freedoms and constrained food, most people who enter the prison system survive. Suggesting that most humans can adapt and not die in conditions not unlike the ISS, albeit with a range of long term effects due stress and related conditions.

Taken together that suggests that if you have no ethics probably at least 50% of the adult population could be turned into an astronaut and not have them die straight away, the question is why this would be a good idea?

  • $\begingroup$ Interestingly, ESA has announced that they are explicitly aiming to have at least one physically disabled astronaut in the next class. $\endgroup$ Commented Jul 9, 2022 at 10:01
  • $\begingroup$ @JörgWMittag Had seen discussion back to the 80s that space station crews should be selected from those missing legs since you reduce your life support needs by a claimed 20%, would be interesting to know what those who have actually lived in space think, since suspect legs are still useful for positioning yourself to use your arms. $\endgroup$ Commented Jul 9, 2022 at 10:34

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