On the one hand, space travel is a completely novel technology and less than 1000 people have traveled outside the planet. On the other hand, every accident in space involving humans is treated as a big deal (such as the Challenger disaster) and there's an implicit assumption that space travel must be safe.

But wouldn't it be better for space exploration if we inherently assumed space travel is incredibly risky and that astronaut deaths are to be expected? I.e. if the Challenger disaster was treated as a cost of doing business, the Space Shuttle program might've still been operational. Obviously astronauts would have to be informed about the potential risks, but I'm sure there would still be tens of millions of people willing to apply for the job.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage
    Jul 6, 2022 at 13:42
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    $\begingroup$ I disagree that the question is wholly opinion based, and think it should be re-opened. It should be possible to find reasoned, on-the-record debates around the issue of safety (certainly the committees discussing the Shuttle disasters would qualify). Likely supporting quotes could be inserted into some of the existing answers with no other edits. $\endgroup$
    – Bear
    Jul 12, 2022 at 15:53
  • $\begingroup$ It's scale. Space flight is not safe. Parking downtown is not safe. Breathing is not safe. $\endgroup$ Jul 25, 2022 at 11:55
  • $\begingroup$ "But wouldn't it be better for space exploration if we inherently assumed space travel is incredibly risky and that astronaut deaths are to be expected?" People dealing with space activities know the risks, from the astronaut family to the insurance company. I guess you know that already, so who's "we"? is it media? politics? public opinion? It's not clear. $\endgroup$
    – mins
    Jul 27, 2022 at 21:36
  • $\begingroup$ @mins if they knew the risks, why was the Challenger disaster a big deal? Shouldn't everyone have just shrugged and moved on to improving the engineering design for the next launch? $\endgroup$ Jul 28, 2022 at 0:31

8 Answers 8


But wouldn't it be better for space exploration if we inherently assumed space travel is incredibly risky and that astronaut deaths are to be expected?

NASA and Roscosmos do assume space travel is inherently risky and that astronaut / cosmonaut deaths are to be expected. NASA asks their astronaut candidates (with a psychiatrist present to evaluate the responses) if the ASCANs accept that spaceflight is inherently risky and that they may die if accepted into the astronaut corp.

The goal is to make it so that 99.73% of one-way space flights end up with no one dying or suffering serious injury. The typical consequence of a serious mishap is death for all on the vehicle. That is an incredibly low bar.

Imagine that 99.73% safety margin was the safety margin for one-way car trips. Many people in the US make well over 1000 one-way car trips per year. They drive to and from work, to and from a store, to and from a gas station, and so on. If 99.73% of those trips was "safe", the odds of surviving a year involving 1000 such one-way trips is less than 7%. People would think twice (multiple times) before hopping in a car.

Imagine that 99.73% safety margin was the safety margin for commercial plane flights. There are 115000 commercial plane flights per day. If 99.73% of those flights didn't involve death for all involved, that would mean over 300 flights per day that did involve death or serious injury. Hardly anyone would fly under such circumstances. It took two fatal crashes separated by several months of Boeing's 737-MAX for the 737-MAX fleet to be grounded worldwide for well over a year.

One final reason that that 99.73% safety margin is an incredibly low bar is that that is the design goal. Vehicle designers et al. work very hard to achieve that goal. Testers, simulation designers et al. work very hard to test whether that goal is met. However, just as six-sigma manufacturing strives hard to get the design defect rate to about four per billion, the reality is that the actual defect rate, even with six-sigma manufacturing in place, is about 3.4 defects per million.

Vehicle designers, software designers, testers, et al. inevitably miss some of the things that can go seriously wrong with a crewed spacecraft. The design goal of less than 3 serious mishaps per 1000 flights is most likely closer to a serious mishap every few hundred flights or so in reality.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage
    Jul 6, 2022 at 13:45

I think you're mixing up public perception vs engineering reality. For example, you mention the space shuttle...

if the Challenger disaster was treated as a cost of doing business, the Space Shuttle program might've still been operational

You have some facts mixed up.

The space shuttle program continued after the Challenger disaster in 1986, and even after the Columbia disaster in 2003. The flights resumed despite continuing to have the same problems that lead to Columbia breaking up: shedding debris striking the heat shield during launch. Instead they mitigated the risk with inspections and the ability to repair the heat shield in space.

Even so, we would not be flying the Space Shuttle today.

The real reason why the space shuttle program was shut down was that it was old, risky, and waaay too expensive. It was designed to be reusable so it could build Space Station Freedom in the 90s and then shuttle back and forth between the Earth and the station at the pace of dozens of launches a year. But Freedom didn't happen (it eventually became the ISS). With no station for the space shuttle to shuttle to, flights were infrequent and the whole concept wasn't economically viable.

In 2004 it was decided the Shuttle was needed to ensure the ISS was built. Meanwhile a newer and cost effective crewed vehicle would be built in 2008, the Crew Exploration Vehicle aka Orion. With a new vehicle flying, the shuttle would retire in 2010. Orion never happened, but they retired the Space Shuttle anyway. It was too old, too unsafe, and too expensive.

So space is risky. But you want to mitigate that risk for several reasons. Here's the most important one: If the rocket blows up, the mission fails. The mission was the whole point.

Here's some other reasons:

  1. Space hardware is very expensive, particularly the payloads. Nobody wants their billion dollar space telescope blowing up on the pad.
  2. Space launches are very public. I watched the Challenger disaster live on TV in school.
  3. Space launches are a point of national pride. They represent the pinnacle of nation's technological achievement and it's politically embarrassing to have it blow up.
  4. We value human life.
  5. Astronauts are considered heroes.

It's one thing to blow up empty uncrewed rockets while you're developing new technology, but it's an entirely other thing to put highly trained heroes, and the mission and the very expensive hardware and all the effort, at unnecessary risk.

It is expected that they will do everything we can to mitigate the risks both to the people and to the mission.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage
    Jul 7, 2022 at 13:29
  • $\begingroup$ Space exploration is risky, deaths cannot be excluded, but for Challenger the Congress report clearly indicated the first reason for not mitigating known risks correctly was the political pressure and the 24 flights a year unrealistic schedule imposed to engineers by NASA management. See page 3. I believe this statement was a potential key contribution to safety as it forced NASA to rethink it's decision and quality management processes rather than blaming engineers alone, a point you didn't mention. $\endgroup$
    – mins
    Jul 28, 2022 at 10:46

My heavens… my sweet heavens. I’m going to try hard to maintain my composure and professionalism, but it’s hard as a space professional to deal with debasing of our work.

The very notion that shooting up one more person means one more person shot up… and therefore “more done git”… is a child’s notion of space exploration. Much like the schoolchildrens’ experiment of putting up an ant colony into orbit aboard the shuttle, when given a chance in the late ‘80s to fly their own experiment. Because ants in space! In space! They’re in space! (I wonder if this is how Christian ecclesiastics feel about Santa Claus as theology.)

The notion of humans in space because humans in space is a late-‘50s notion, already dated by the late ‘60s, let alone the mid ‘70s. Human presence aboard space vehicles needs a mission requirement and a success criterion, which in the first few years was simply proving (in the sense of field trials, i.e., proving grounds) that it could be done, then proving further details and decimal places on the criteria. After reasonably concluding that it could be done, humans in space because humans is then a stunt, not a fulfilled requirement. This was the path of the aviation industry, after the experimental era (1900s to ~World War I) led to the Barnstorming Era (Air circuses and sideshows), because neither air mail nor airlines turned a profit without massive subsidization.

We are not staging circuses for public amusement… or at least, I refuse to. Private billionaires are tacitly doing so, and as long as it’s their money then they can blow it. And yet, neither Branson, Bezos, Ansari, or Musk are interested in throwing their billions to hacks and amateurs. In the direct sense, a billion can disappear before you realize it, and then you’re down a billion. In the operations sense, these vehicles (and more) operate in ranges, airspaces and orbital zones that result in consequences for failure. Rutan had a propellant explosion ON THE GROUND that killed a few of his employees- even aside from labor violations, you won’t keep your operation running when your own staff fear for their jobs/lives/whatevers. Dropping a live rocket on a populated area can also make a billion disappear before you know it, so these (current) billionaires are thinking twice before approving plans and cutting metal.

And those are the stunters, at least at first glance. Branson and Bezos actually hope to (eventually) make their money back and then some by selling tickets; Musk plans on making the investment pay back via Starlink, third-party payloads, DoD/NASA contracts, etc. (There’s the Mars PR, but it’s possible that the notion of “Mars!” is a marketing/advertising gambit for the benefit of the greater operation.) The rest of us are NOT doing some stunt: space because “space!”.

Therefore, making the success criteria lower, not higher, is less than possible, it’s actually harmful to our industry (at least, by certain metrics). The loss of schedule due to post-investigation grounding leads to loss of funds (time is money), loss of staff (trained engineers can jump to other fields), loss of capital via investor flight… and in the general sense another loss of confidence may lead to yet another “space winter” just like for AI.

Santa Claus can lower his sleigh margins because… Santa and the sleigh aren’t real, and the presents will arrive without consequences. You can also search for the schoolchildrens’ space ant project to see what waste looks like (though no real monetary consequence occurred). Meanwhile, those of us with real paychecks for successfully meeting our real mission criteria- not amusing a fickle and distractable audience- won’t waste our time and effort.

My source: over twenty years of academic/DoD/NASA work. With paychecks to match, because the goal wasn’t amusement. (Therefore, almost all of those projects were uncrewed, not wasteful.)

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    $\begingroup$ Well put. I think the OP is suggesting not grounding other work / launches for an investigation after an incident, so instead of lost time, you'd potentially have more lost payloads and equipment if any of the other launches had the same problem that caused the first incident. That would pretty clearly be even worse, unless the only resource you were short of was time, not money, lives, manufacturing, or morale. e.g. if we knew the Earth was going to be uninhabitable in 3 years, and turned the entire budget of the world to building space habitats large enough to grow crops and live in. $\endgroup$ Jul 6, 2022 at 4:28
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    $\begingroup$ (And even then, with putting people into space as the only priority for the entire world, expecting 20% failure rate seems way too high, even for unmanned stuff. The days of early experimentation are long done, and we can simulate and automate much better.) $\endgroup$ Jul 6, 2022 at 4:30
  • $\begingroup$ Could you please clarify AI in "yet another “space winter” just like for AI"? $\endgroup$
    – sehe
    Jul 6, 2022 at 12:53
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    $\begingroup$ -1 This does not address the question "Why is it assumed that space flights have to be safe?" but instead rebukes the asker for daring to ask it. Regardless of how you feel about the question, I don't think that's appropriate for a Stack Exchange answer. $\endgroup$
    – Bear
    Jul 12, 2022 at 16:04
  • $\begingroup$ @sehe I thing this is comparing how the field of space exploration and the field of AI research have both had breakthroughs followed by intense advancement and optimism followed by "winters" of frustration, slow progress, and cynicism. $\endgroup$
    – ikrase
    Jul 15, 2022 at 5:45

Why is it assumed that space flights have to be safe?

It is because of a concept called Duty of Care.

Which basically boils down to, not willingly or knowingly harming others. To do one's best to ensure other people are not adversely affected by whatever one does or does not do.

People have a right to expect they can go about their lives, including work, and not be injured or killed and employers have a duty of care to ensure their employees and contractors are not injured or killed while in their employ.

Space flights, like any other activity, would cease if the failure rate was 100 percent or close to it.

Anything that anyone does has a risk of injury or death associated with it. The risk can never be eliminated, but it can be reduced and that is one of the functions of Duty of Care.

During the development of the Apollo space program, astronauts were concerned about the lack of safety with the Block 1 version of the command module, but in the rush to get ahead in the space race very little, if anything was done until the Apollo 1 disaster which claimed the lives of three astronauts.

That prompted a redesign and a cessation of testing using astronauts for 18 months. The Block 2 version "eliminated the dangers of wiring", that initiated the fire in Apollo 1.

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$\sf{The\ Apollo\ 1\ crew\ expressed\ their\ concerns\ about\ their}$ $\sf{\ spacecraft's\ problems\ by\ presenting\ this\ parody\ of\ their}$ $\sf{\ crew\ portrait\ to\ ASPO\ manager\ Joseph\ Shea\ on\ August\ 19,\ 1966.}$

The Apollo 13 incident resulted in a spare oxygen supply being installed on the opposite side of the service module.

I forget which book I read it in, but Frank Borman's wife was very unhappy with senior management at NASA when she learned her husband was going to fly on an untested mission to the Moon. She didn't like the idea of her husband taking the risk of going to the Moon in Apollo 8.

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    $\begingroup$ @JonathanReez: Employees dying at work is never a good look. It's bad for PR & eventually people start to question the organization's social license to operate. Remember, NASA is a government owned entity. Why would the American people want their taxes to pay for people to be killed on the job? It also sets a dangerous precedent, "if it's good enough for such an organization to have lax safety standards, then why not elsewhere?". Besides, what's there to be gained by people dying on the job & space exploration organizations & companies wasting money on a failed space craft or other equipment? $\endgroup$
    – Fred
    Jul 4, 2022 at 4:09
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    $\begingroup$ @JonathanReez: Take another example: the military. Everyone who joins the military knows there's a possibility they may serve in military conflict and they could be injured, maimed, suffer mental damage or die. No-one likes it when the body bags just keep returning home. They eventually start asking "why are so many of our fighting men & women dying, why don't we end this war? Why are we still involved?". Have a look at what happened in Korea, Vietnam, Iran, Somalia, Afghanistan. $\endgroup$
    – Fred
    Jul 4, 2022 at 4:30
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    $\begingroup$ @JonathanReez the morality of sending people to their deaths so willingly aside, investing some extra time and money into making the mission as safe as reasonably possible seems like a good idea when the people you are launching into space take decades to train. $\endgroup$ Jul 4, 2022 at 13:52
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    $\begingroup$ @JonathanReez what debate on the safety of flying to Mars? We don’t even have a rocket that can take humans to mars. That discussion is not the blocking factor. And how would it be faster to colonise mars if we launch 5 rockets and only 4 of them get there? We’ve lost 20% of the cargo / people / recourses right out the gate. It feels like asking “why we do maintenance on trucks. Couldn’t we get there quicker if we just left now”. And finally, you seem to have a very caviller attitude towards death. Government sanctioned Russian roulette doesn’t sound like a particularly healthy plan. $\endgroup$
    – Tim
    Jul 4, 2022 at 14:47
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    $\begingroup$ @JonathanReez The actual death rate for US soldiers serving in Afghanistan seems to be about 0.5%, which is much lower than your suggested acceptable rate for astronauts of 20%. And death is a soldier’s business. Science is an astronaut’s business. $\endgroup$ Jul 5, 2022 at 3:38

Ask the Rooskis about that. It's not just that unsafe space travel is Bad For Business (turns taxpayers away from future investment), it's that, like any transport mode, space travel has to eventually be fit for everyone. Yes, a certain amount of risk is acceptable and also to be expected. However, the mitigation of that risk has to be a top priority to show that the travel modality can be viable long term.

600 years ago travel from the centers of "civilization" to The New World was considered dangerous not because the ship might sink of its own accord before landfall, but because of the inherent dangers of any long sea journey. How many adventurers do you think would be willing to risk dying in the open sea just because the vessel was a piece of junk?

Let's focus on getting to the places we want to visit and also getting back safely. There's no reason safety can't be a top priority in doing so. Modern technology allows us to sidestep risks that had to be accepted with gritted teeth in past generations. Keep yer eyes on the prize, dooode.

  • $\begingroup$ "space travel has to eventually be fit for everyone" - requires citation. I think that only seems self-evident because you labeled it "travel". In reality the vast majority of space missions are more like "space transport", "space presence", "space mobility". $\endgroup$
    – sehe
    Jul 6, 2022 at 12:55

Frame Challenge - the Question is Unclear

The proposal is to reduce safety for some reason. The gain in that tradeoff is never stated. Is it it to reduce schedules, reduce cost or what?

Also, what's the long-term benefit of the tradeoff? What's the end-goal here? Again, that's never stated. Answers make assumptions about those two items but the asker never comes right out and says.


Astronauts understand that space travel is risky, they are willing to accept the risk if the mission is worth it. The astronauts who flew on the Hubble repair missions thought that their work to enable the great science that Hubble collects is worth the risk of life, but a proposed mission to recover Hubble so it could be placed in the Smithsonian was not considered worth the risk.

NASA doesn't want suicidal astronauts. The psychological exam is full of subtle ways to fail out of the program. When the NASA psychologist asks you if you want to come home from your mission, the only correct answer is yes, any other answer will get you bounced out of the program.

Space flight is not the same as commercial air travel. Air travel is generally safe because airlines make thousands of flights per day and the experience builds up. The technology is not comparable, it takes 900 times as much kinetic energy to put something or someone into orbit as it takes to fly them in a passenger aircraft. Any vehicle that can propel itself into orbit is going to be inherently dangerous. We take our children on airplanes to go visit Disney World, would you put your children on a space shuttle?

It might be fair to compare space flight to military service. People who volunteer for military service know that there is a possibility that they could die in combat, but they are willing to accept that risk to serve their country. The early space program was the moral equivalent of war by other means. Frank Borman said that he did not go to the moon as an explorer, he went as a soldier in the cold war.

Astronauts are not the national heroes that they were in the early days. How many Americans can name the current crew members of the ISS? How many can name one of the other six Challenger crew members aside from Christa McAuliffe?

In some respects manned spaceflight is a relic of the early science fiction stories, in which a human crew had to explore space because early SF writers failed to imagine that robotic spacecraft could collect data and radio it to Earth without a need to come back. With few exceptions, such as repairing Hubble or collecting rocks on the moon, most scientific missions can be done just as well by robots.

Humans also are very irrational about risk assessment, worrying a lot about very rare possibilities and accepting much more common risks such as smoking and poor diet. We lose 30,000 Americans in highway accidents each year but we are willing get into our cars every day because we rationalize that it won't happen to us.

  • $\begingroup$ astronauts who flew on the Hubble repair missions thought that their work to enable the great science that Hubble collects is worth the risk of life - those were the currently hired astronauts though. NASA would still get thousands of excellent applicants for the mission to recover the satellite, just not the ones currently hired. $\endgroup$ Jul 6, 2022 at 3:37
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    $\begingroup$ @JonathanReez At this point it appears you indeed are trolling. It's not a good look. $\endgroup$ Jul 6, 2022 at 7:21
  • $\begingroup$ The point is that NASA screens astronaut candidates for emotional stability, they don't want daredevils and people who take risks for no good reason. I would not trust my billion dollar space telescope to a crew that is lacking in maturity and good judgement. $\endgroup$
    – n8fgv
    Jul 6, 2022 at 13:39
  • $\begingroup$ @n8fgv there's nothing immature about undertaking a 20% risk of death for the sake of science/humanity, assuming such an increase in risk would in fact be beneficial for rapid iteration in the industry. Dying at 90 in a retirement home isn't the only acceptable way to end your life. $\endgroup$ Jul 6, 2022 at 22:04

Why do you think deaths are the issue here?

The issue for all of these isn't the deaths of people. It's failure of the mission.

Challenger wasn't just going up there to take some pretty pictures. The primary mission was launching one of NASA's TDRS satellites, which (after all the birds were launched) let NASA remain in permanent contact with everything in orbit, all the time. NASA may publicly claim that this was intended to allow continuous communication with civilian space missions - but it's not exactly a secret that this was also used to allow permanent contact with US spy satellites. In other words, losing that satellite meant a delay in getting this network established to use spy satellites to their full potential, and a more serious vulnerability if anything went wrong with the first (and at the time, the only) relay satellite in orbit.

Columbia wasn't just up there for fun either. It was a science flight, running experiments which needed to be in zero-G, and testing orbital observation kit. Through good luck, a lot of the experimental data was salvaged, but only through luck. Without that luck, all those experiments would have been lost and people would have had to do it again. It's not cheap to put stuff into orbit, so this isn't just done on a whim. Some university or government department has to find another few million bucks to do it all again, and that's not trivial.

Ariane proved that if you want to get anything into orbit, it's way more reliable and way cheaper to use remote/automated systems. The infrastructure to keep humans alive is heavy and fragile. There simply isn't a mission benefit to people being up there. Even exploration doesn't need people.

Where do we need people? Precious few places, actually, and that's why the ISS is such a white elephant.

The only place which genuinely needs humans involved is if you plan to stay wherever you're going. The aim of going to the Moon was not simply to go there, it was to establish a missile base there which the Russians could not easily target. By 1969 it was pretty clear there was no military justification for that, and the vast cost of setting up and maintaining a base (especially given technology levels of the time) was unjustifiable. One of the few benefits of the ISS has been to study long-term spaceflight, which is a key enabler for any future colonising mission to Mars.

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    $\begingroup$ NASA distinguishes between loss of mission and loss of life. It is a huge distinction. $\endgroup$ Jul 4, 2022 at 15:51
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    $\begingroup$ Re The aim of going to the Moon was not simply to go there, it was to establish a missile base there which the Russians could not easily target. That is a false meme. From the outset, the goal was to just go there. Just getting there was the goal that the US foresaw as the first opportunity of substance where the US was likely to succeed over the USSR. A space station, even a primitive one, was ruled out as a goal as the US foresaw the USSR being the first (and they were). Other goals where the US did foresee beating the USSR to the punch were deemed to be not substantial enough to count. $\endgroup$ Jul 4, 2022 at 15:57
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    $\begingroup$ The loss of astronaut lives is absolutely a big concern because space travel is a human endeavor and humans have feelings and emotions. Even a cold, calculating person must acknowledge the political aspects of NASA and how the loss of Christa McAuliffe aboard Challenger was a huge emotional blow to the public support of NASA and space exploration. Without public support, NASA does not get funding. American taxpayers do not want to spend billions of dollars to see it blow up and kill teachers and astronauts. I choose to believe it’s because we have heart and compassion. $\endgroup$ Jul 5, 2022 at 3:53
  • $\begingroup$ @DavidHammen: Conceptually, that notion might seem attractive, but was any serious consideration ever given to overcoming the physics involved? A lunar satellite which had enough fuel to return to Earth would have far less maneuvering ability than would an attack rocket or even a terrestrial satellite that was intended to be capable of evasive maneuvers. I think physics would favor an attacker in either case, but the lunar situation would be worse. Landing on the Moon might offer some defensive prospects, but the amount of fuel required for a rocket to proceed from the Moon... $\endgroup$
    – supercat
    Jul 5, 2022 at 18:56
  • $\begingroup$ ...directly to Earth, without a lunar-orbit rendez-vous, would be rather huge. Add in the fuel required to get the craft to the Moon, and then have it land safely on the Moon, and the fuel to round-trip payload ratio would become totally impractical. I could see some use for some moon-based communications infrastructure, but the fact that most parts of the planet would only be able to communicate for about twelve hours every twenty-four would be a rather substantial disadvantage. $\endgroup$
    – supercat
    Jul 5, 2022 at 18:58

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