"Cousin Ricky" <ric### [at] yahoocom> wrote in message 
news:web.458015c7ff75702c85de7b680@news.povray.org...
> "Tim Attwood" <tim### [at] comcastnet> wrote:
>> I'm of the opinion that a large enough power source, such as
>> a nuclear reactor, could produce enough electric power to fuel a large
>> ion thuster. If a thrust to power ratio of around 50 mN/kW is assumed, 
>> and
>> a total ship weight of 10 tons then we're looking for a power source of
>> about 2 gigawatts. This would let a ship accelerate a little over 1G for
>> extended periods. Such a ship could make a round trip to Alpha Centari A 
>> in
>> about 9 years. If such a vehicle was unmanned then little of the 
>> radiation
>> shielding would be needed, which is what turns a reactor into a big 
>> building
>> with 6ft thick cement walls.
>
> 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.

You're thinking about this way too hard! ;-)

Jon

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