And when they arrive all their muscle will be gone due to lack of gravity and then the lower gravity on Mars.
If they were able to return to Earth they would probably be in a wheelchair or bed-ridden for months.
This is something none of these "human space civilization" people realize. We are never colonizing space! Our physical bodies are literally made from the minerals of the Earth and our bodies depend on so many things that we can only get on Earth.
Problems with living in space indefinitely:
1) storage: where do we store all of the water, food, medical supplies?
2) gravity: our bodies, especially our bones disintegrate with no gravity and our muscles atrophy away. There are no gravity machines despite what Star Trek and The Orrville seem to imply.
3) oxygen: where do we get endless supplies of oxygen in space? Even if we have filters that take our CO2 breath and recycle it we still lose some oxygen to our cells so we must continue creating it to survive.
4) distance: things are so far apart in space it would take generations just to get to another star system. There is no "warp speed, Scotty" like on Star Trek. There would be no purpose in colonizing anything in our solar system because when our Sun burns out the whole solar system is dead.
5) protection: flying through space it's just a matter of time before the space craft hits a rock (asteroid) coming in the other direction too small to see. Two objects from opposite directions colliding would cause a catastrophic impact no one could survive.
This science fiction/fantasy is fun to read but people are taking it way too seriously.
