"Bill Pragnell" <bil### [at] hotmailcom> wrote in message 
news:web.458138e3ff75702c731f01d10@news.povray.org...
>> 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.

I omitted relativity, the 9 years would be shipboard time, including
some fudge factor for midpoint turn around time and time for the
actual mission...
We don't really know what would happen at those speeds, we
only know that we have observed relativity at the slow end of
the curve IRL.

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