I solved exercise 6.1 of "Gravitation" by Misner, Thorne and Wheeler and reached the impressive result that it takes only 11 years of proper time to reach the center of the Milky Way (~30,000 light years away) if you accelerate at one earth-gravity (10³ cm/sec²) for half the trip and decelerate at the same rate for the remaining half.

What I did was to simply use the formula x = g^-1 cosh gτ. If I got relativistic units right, then g = 1 (in light-years) and x = 30,000, which yields τ = 11 years. But since these accelerations are quite mundane (lower than that of a Formula 1 race car), I suspect I went wrong somewhere. Did I?