posted on Jun, 13 2004 @ 03:19 AM
That is quite difficult, because special relativity and accelerated observers requires a lot of math to solve.
(Baez' site is really great!) has an explanation which contains
t = c/a arccos ( a*d/c^2 + 1)
where c is the speed of light, a the acceleration, d the distance in the earth frame and t the time of those inside the spaceship.
Because we accelerate half the way, for us the formula becomes:
t = 2*c/a arccos ( a*1/2*d/c^2 + 1)
t = 2*300*10^5 arccos( 10*1/2*40,5*10^15/ (300*10^6)^2 + 1)
This gives you a time of 110834765 seconds or 1282,8 days or 3,51 years.
[edit on 13-6-2004 by amantine]