starship-design: Help with formula

[Steve VanDevender <stevev@efn.org>]

Zenon Kulpa writes:
 > Please, I have lost it somewhere, no time to search or derive,
 > what is the formula for Earth time & crew time
 > in the (one-way) flight with constant acceleration = 1g 
 > (half way +, half way - ) depending on the distance (in ly)?
 > 
 > Thanks, 
 > 
 > -- Zenon

For one-way acceleration:

t = (c / a) * acosh(1 + (a * d / c^2))

t = elapsed time
c = speed of light
a = acceleration
d = distance traveled
acosh = inverse hyberbolic cosine function