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Re: Fly to the moon question



I stand corrected.  I meant "efficient" in a practical sense, since the 
energy to drive an ion engine can come largely from virtually unlimited 
solar power, and the small reaction mass carried onboard for propellant 
can be expelled at far higher velocity than is possible with a chemical 
reaction, so the propulsion means a much smaller package to lift from 
the surface .. but you're right, it's not the right word to use ..

On Friday, Nov 21, 2003, at 20:42 US/Central, Assi Friedman wrote:

> Bruce,
> I have one small comment for the statement: "more efficient form of
> propulsion"
> Ion and all electric types of propulsion systems are very inefficient 
> but
> for some missions are very practical. For classic propulsion systems 
> the
> total impulse is related only to the mass of fuel and oxidizer carried 
> on
> board. Once the combustion process is started is it self sustaining. 
> With
> solid and hybrid you need to introduce initial energy to start the
> combustion. With bi-prop we have hypergolic process which is self 
> starting
> and mono-prop is started by a catalyst. All of those types of 
> propulsion
> systems are mass starved.
> In the case of Electric propulsion, we are energy starved. The fuel 
> doesn't
> have an oxidizer per say but we use electricity to energize it and 
> shoot it
> out to change the vehicle's momentum. In order to be able to do so, we
> gather lots of photons from the solar panels, convert them, store 
> them, and
> then run them into the motor in order to operate it. If you look at the
> efficiency of the propulsion system it is horribly inefficient, but for
> missions that need a large total impulse over time, it becomes 
> practical. In
> essences, we kind of gather a part of the oxidizer on the way, even 
> though
> it is wrong if we look at the chemical reaction. Without the power we 
> dump
> into the system, the propulsion is useless.
> Assi 4x1kx/kk7kx
>
>
           --... ...-- -.. . -. ..... ...- -...
                   Bruce Bostwick N5VB

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