power sat energy payback.

[Alberto Monteiro]

Keith wrote:
>
>>> There is plenty of energy around if we can figure out how to get
>>> it.  For example, a solar power satellite repays the energy needed
>>> to lift it to GEO in about a day (at 100% efficiency).  Five percent
>>> efficient rockets would replay the lift energy in 3 weeks.
>>
>> This is almost surely wrong. Did you do the math?
> 
> Yes.
> 
> Specific orbital energy is u/2r, (398,600/42,000)/2 or -4.75Mj/kg
>
Ok
 
> Potential is -9.5Mk/kg and kinetic is 4.75Mj/kg
>
> Potential at the earth's surface is -62.6 MJ/kg; the
> difference is 53.1Mj/kg.
> 
Ok.

> Using a space elevator, 
>
I didn't know you were invoking Magic. "If I had magical fairy
godparents I would make 2 + 2 = fish".

Try to do the same exercise using chemical rockets :-)

Alberto Monteiro