[JPLeRouzic]

Thanks for the insight. I mostly agree but I guess there are many humans on Earth that live without help available within a few hours, for example sailors in international seas.

Even traveling abroad in a developed country carries some risks, if you have some medical issue and are unable to explain yourself because of lack of medical vocabulary, the consequences may be dire.

[ben_w]

While true, I think you're underestimating the extra difficultly of space here.

Mars is colder than Antarctica, drier than the Sahara, has an air pressure much much closer to vacuum than it is to even the top of Mt Everest (and a quarter of it condenses each Martian winter), the air it does have is 95% CO2 and 0.174% oxygen, the soil is as polluted as a superfund* cleanup site, the sunlight is at best 50% of the Moon's due to distance from the sun but planet-spanning dust storms can reduce that, because of the lack of free oxygen there's no free ozone layer and combined with the thin atmosphere in general it has higher ionising surface radiation despite the lower sunlight, and the return time to Earth even for nice options like VASIMR** are 39 days in the best launch window.

To give a toy example: If the water supply suffers a catastrophic loss, everyone dies in almost all circumstances before being able to get help (even if we had/when we get working VASIMR solutions at this scale, right now most discussions assume much slower and more delta-v-efficient Hohmann transfer orbits).

Same incident happens on the moon, emergency evacuation or resupply is possible before death by dehydration.

To get back to Earth from Mars with that kind of time constraint, we'd need an engine that can sustain close to 1g acceleration for about 2 days at closest approach; at maximum separation, unless I've messed up the formula, 1g would still take 4.7 days (with mid-point flip for deceleration). Basically, mytailorisrich is correct to describe this as needing "near Star Trek level" tech, because the closest we have to an inertial dampener right now is a very big magnet pushing on the water inside our bodies***.

* https://en.wikipedia.org/wiki/Superfund

** Claim I last heard was 39 days for a 200 megawatt reactor "with a power-to-mass density of 1,000 watts per kilogram", the good news is we can almost do that power-to-mass density with PV after accounting for Mars-gets-less-sun: https://www.globenewswire.com/news-release/2023/10/25/276652...

*** The difficulty of making this useful is comparable to the difficulty of launching a spaceship with a big magnet on the ship that pushes against Earth's own magnetic field.

As I recall from last time I did the maths, if you did it with copper, the copper would boil before you did much useful.