: One thing to factor in is that the Marathon was driven by a Bussard ramjet
: and so was continually accelerating the entire time in transit, scooping
: up fuel from the interstellar medium as it went. So it's not just a matter
: of launching it from Sol at its average cruising speed; it's a matter of
: launching it at a speed which, taking into account continuing acceleration
: (which we'd have to calculate separately, factoring in things like the
: density of the interstellar medium plus all the technicalities of the
: hypothetical drive mechanism), leaves its average cruising speed as such
: (meaning much greater cruising speed by mid-journey, before it has to
: start braking).
Yep. Time to sit back and watch as the story forum independently discovers calculus.