> Does this estimate take relativistics effects into account?  (I've long
> forgotten how to do the math.)  A vehicle that gets to Alpha cen in 4.5
> years has to go pretty close to the speed of light.  The relativistic mass
> gain would surely affect the thruster's ability to maintain acceleration.

I think 9 years is more likely to be the one-way trip, assuming you
accelerate at 1g to halfway and then turn round and decelerate ass-first
the rest of the way. A round trip would be more like 16-18 years. The crew
would only see it as 7-8 years, of course.

This is based on this page:
http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

I haven't checked the maths but it looks right!

The mass gain is irrelevant, really. From the ship's point of view,
acceleration is constant and the universe deforms. :-)

Bill

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