Humanity needs to leave earth and travel to a new home planet. Given that the technology for fusion reactors is available, how fast could they realistically travel?

There are two scenarios I'm interested in:

  • Living humans in a spacecraft (in hibernation or on a generation ship)
  • No living humans, only cargo with DNA samples

The questions are:

  • How much acceleration would be survivable for a human?
  • How fast could an spacecraft go without compromising structural integrity?

It appears that nothing above 10% of the speed of light would be realistically doable.

  • $\begingroup$ While these are interesting questions, Worldbuilding really isn't the place for them. This particular forum focuses on building up of fictional worlds; your question is largely one of plot & technology. I'd suggest asking over in the Scifi & Fantasy forum for the story aspects and in the Physics forum for the more sciencey aspects of your question. $\endgroup$
    – elemtilas
    Feb 24, 2018 at 16:27
  • $\begingroup$ Speed is relative If you are at high speed relative to the asteroids (with spikes; the worst kind) you are moving thru, they might compromise your structural integrity. If you are at high speed relative to a distant star and you have nothing in your path, no problem. Excellent stats on humans and acceleration here: worldbuilding.stackexchange.com/questions/88002/… $\endgroup$
    – Willk
    Feb 24, 2018 at 17:24
  • $\begingroup$ You are asking two questions here, it seems. It is better to limit yourself to one question per question. Especially under hard science tag. Are you sure you even need hard science? Wouldn't science based suffice? $\endgroup$
    – Mołot
    Feb 24, 2018 at 17:58
  • 3
    $\begingroup$ @John - "How fast could an spacecraft go without compromising structural integrity?" Well, some accelerations are too strong for structural integrity, but as long as the acceleration is acceptable there is not speed limit. However, the faster the the speed the worse the encounters with grains of space dust or hydrogen molecules will be. At high enough speeds hitting one would be like exploding an atomic bomb on the ship. The top speed may be limited by the ship's protection against such encounters. $\endgroup$ Feb 24, 2018 at 18:43
  • $\begingroup$ @M.A.Golding True any space debris would be lethal without proper protection. I'm not really familiar with the physics, but my guess would be that keeping the spaceship together under such massive acceleration is much harder then protecting against particle or atom size debris. Could the fictional spacecraft even go so fast that atoms would be become deadly without killing the crew? $\endgroup$
    – John
    Feb 24, 2018 at 22:42


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