Air travel is the safest method of transportation, with 0.07 deaths every billion passenger-miles. While space travel certainly has a higher fatality rate per-space-traveller (~3%)1, 2, where does it rank when we look at passenger-miles, especially given the vast distances travelled (people on the ISS for long periods of time)?

The statistics for other methods of transportation appear to only consider fatalities, so that is good enough for me – although I'd be interested in how many non-fatal injuries there actually are in space travel!

  • $\begingroup$ You may take a look at comparision like this one $\endgroup$ – Manu H Apr 5 '18 at 5:48
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    $\begingroup$ Deaths per passenger-miles skews the result in favor of space travel because speeds are so high. Deaths per flight hour may give a better comparison. $\endgroup$ – Hobbes Apr 5 '18 at 8:22
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    $\begingroup$ Generically, I think the per-passenger-mile comparison is only useful for destination-to-destination travel (i.e. what's the safest way to get from A to B). Space travel doesn't really fit because its B destinations are generally unique (unless you want to say e.g. flying the Space Shuttle is a shockingly unsafe way to get from LC-39 to the CCAFS runway). $\endgroup$ – Erin Anne Apr 6 '18 at 19:47
  • $\begingroup$ @ErinAnne It's not even a fast way to make that trip! ;) $\endgroup$ – Russell Borogove Apr 6 '18 at 20:14

According to WP:

The number of deaths per passenger-mile on commercial airlines in the United States between 2000 and 2010 was about 0.2 deaths per 10 billion passenger-miles

The ISS is by far the largest contributor to crewed spaceflight time in the 21st century, being continuously occupied by 3-6 people for over 17 years since November of 2000, during which time it's achieved somewhere between 8 and 16 billion passenger miles. Shuttle flights from 2000-2011 make up something like 10% as much as that; Soyuz flights are accounted for by my ISS crew estimate, and other crewed spaceflight missions are negligible.

Over the same time frame, 7 astronauts have died (the crew of Columbia on STS-107).

That makes space travel about 20-40 times more dangerous than airline travel by passenger-mile, but it's worth noting that all the astronaut fatalities in the 21st century occurred in that single incident, so we're clearly dealing with statistical outliers here; the "real" hazard rate could be much higher or much lower. In the decade 1991-2000, there were no astronaut deaths, making space flight infinitely safer than air travel; in the decade 1981-1990, there were 7 deaths in the single Challenger incident with far fewer space-crew miles flown to amortize over.

As Hobbes notes, it might be more appropriate to consider the risk by passenger-hour rather than by passenger-mile. In this case, assuming an average of 500 mph for airlines, we get ~0.01 deaths per million passenger-hours. There have been somewhere between 500,000 and 1 million passenger-hours spent on ISS, and again 7 deaths. This makes space travel 700-1400 times as deadly per passenger hour.

26500 miles per orbit * 1440 minutes per day * 6360 days / 92.65 minutes per orbit = 2.6 billion miles per crew member.

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  • $\begingroup$ Are you using the ISS as your only reference point because it's too difficult to determine how many miles manned rockets have traveled or because you expect the contribution from manned rockets to be too low to be significant? If the former, you should make that an explicit assumption which would result in deaths per mile being overestimated. If the later, you should make an attempt to provide some evidence. As it is, all I see is ISS miles traveled divided by deaths in rockets, which doesn't seem to make sense since those are two different vehicles. $\endgroup$ – Ellesedil Apr 6 '18 at 16:07
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    $\begingroup$ Made that assumption more explicit. $\endgroup$ – Russell Borogove Apr 6 '18 at 16:29
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    $\begingroup$ Thanks. I'd argue that a 10% difference in miles travelled is significant, especially if you assume the ISS has allowed for 16 billion passenger miles travelled, but it doesn't change the conclusion much since the difference is already so vast. $\endgroup$ – Ellesedil Apr 6 '18 at 16:36
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    $\begingroup$ Because other components in my estimate vary over a 2:1 range, 10% isn't significant. en.wikipedia.org/wiki/Fermi_problem $\endgroup$ – Russell Borogove Apr 6 '18 at 16:38
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    $\begingroup$ @OrganicMarble We just fly a ridiculous number of airplanes -- 90,000 flights a day full of people compared to ~5000 orbital launches ever and only a few hundred crewed. $\endgroup$ – Russell Borogove Apr 8 '18 at 2:30

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