If we could achieve .5c how long would it take to get there with the physical limits of the human body.
In a Newtonian world:
v = u + at
v-u
--- = t
a
v = 150,000,000 ms
-1u = 0ms
-1a = 10 ms
2
Simple maths suggests 15,000,000 seconds or 250,000 minutes or 4,167 hours or 173 days.
Alaister Reynolds (sci fi author) often has his space vessels accelerating at about 10ms
2 simulating normal gravity for the denizens. It takes a while, but accelerations add up very quickly.
Of course, the challenge comes in finding a way to accelerate something to such a degree for that long.
™ Version 4.2