Re: starship-design: Calculations involving self-powered spaceflight

[Timothy van der Linden <TLG.van.der.Linden@tip.nl>]

Hello Andrew,

>>Furthermore you assume the time to accelerate to 0.9c can be calculated
>>with a non-relativistic formula, well you can but the answer will be far
>>from reality. I can tell you that with a constant 10 m/s/s acceleration it
>>takes 511 days according to the crew and 717 days according to people on
>>Earth to see the ship reach 0.9c
>>The lesson here is that you should really use relativistic equations if you
>>do calculations above 0.5c
>
>I thought that I would only have to increase the mass of the ship as speed
>increased? If I keep my accleration, then I would have thought that mass is
>independant on the accleration, provided I change the force?  if a = (v -
>u)/t, then I don't see how mass increase would affect it...

It depends on your viewpoint:
I prefer to take the view from the ship crew. In their frame the ship keeps
the same mass (except for the decrease caused by the exhaust of fuel).
However the fuel which is exhausted with great velocity relative to the
crew is measured by the ship's frame to have more mass caused by relativity.