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RE: Fly to the moon question



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



-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Bruce Bostwick
Sent: Friday, November 21, 2003 8:46 AM
To: amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] Fly to the moon question


Well, I'm not a "real" rocket scientist, just an amateur with more than
the usual interest in it, but ..

This would work too.  It's basically the same concept, just using a
lower thrust but far more efficient form of propulsion and spreading
out the TLI burn over many successively larger orbits.  The nice thing
about unmanned missions is that you have time to do stuff like that
without really having to pile on consumables for a manned crew, and the
spacecraft overall is much lighter, including fuel, so it can be lifted
into GTO or LEO by a much smaller booster.  (For perspective, it took
the entire S-I and S-II, plus a small vernier burn from the S-IVB, to
get the upper stages of the Apollo missions just to LEO.  The much
smaller S-IVB handled the entire remainder of the job of getting the
CSM and LM into a translunar trajectory.  The kerosene and LOX powered
S-I didn't even get the spacecraft out of the atmosphere .. it staged
off somewhere slightly after Max Q ..)

On Thursday, Nov 20, 2003, at 23:20 US/Central, Timothy J. Salo wrote:

> The SMART-1 spacecraft was launched September 27 into a GTO.
> It is using a electric propulsion system to slowly boost its
> orbit until it is captured by the moon (i.e., over a period
> of sixteen months).
>
> The real rocket scientists among us can undoubtedly provide
> additional insight.
>
"Oh yeah? Well, I speak LOOOOOOOUD, and I carry a BEEEEEEEger stick --
and I use it too!"  **whop!**   -- Yosemite Sam


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