Re: Is this a new cheap way to get material into space?

From: Adrian Tymes (
Date: Thu Mar 01 2001 - 23:56:41 MST

Ken Clements wrote:
> Adrian Tymes wrote:
> > Standard Idea Question: So, what obvious fallacy am I missing in the
> > above? ^_^;
> The obvious fallacy is that you have to lift your energy source. For chemical
> rockets, the reaction mass is also the energy source, so I do not think you can
> beat them.

Actually, I did think of that one. Standard rocket equation:
Mi/Mf = e^(dV/Ve)
Mi = Initial mass
Mf = Final mass (Mi - fuel used)
dV = delta velocity (~9000 m/s, for low Earth orbit)
Ve = exhaust velocity
...and it's that last term that's critical here. Chemical rockets can
get up to 4500 m/s exhaust velocity (at least, the shuttle's liquid
fuel does), and there doesn't seem to be much improvement possible.
Much much higher exhaust velocity == much much lower Mi/Mf, to provide
room for the mass which is your energy source. If the source is light
enough, this also means extra payload (or less Mi for a given payload
mass, et cetera). Railguns with projectile velocities well over 4500
m/s (for example, around 20000 m/s) have been demonstrated.

Can anyone see any other problems?

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