Re: Spaceship One in perspective

From: Jeff Findley (jeff.findley_at_ugs.nojunk.com)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 11:21:55 -0400

"Scott Moore" <samiam@moorecad.com> wrote in message
news:h5iEc.112811$2i5.101000@attbi_s52...
> Jeff Findley wrote:
>
> > When you start talking about launch vehicles to LEO and beyond, solids
start
> > looking very unattractive and hybrids don't look so good either.
> >
> > Jeff
>
> For a beginner to the subject, can you say why that is ?

Generally lower ISP and a higher empty weight than a liquid engine. ISP is
a measure of the performance of a fuel/engine combination and is a bit
lengthy to explain in detail.

As for the empty weight issue, with a solid, your fuel/oxidizer container
and your combustion chamber are the *same* structure, so it's got to be able
to withstand the pressure and temperatures of the combustion chamber. When
you look at a shuttle SRB, pretty much the entire length of the SRB is
(heavy) combustion chamber. These things are so sturdy (heavy), they are
dropped into the ocean (with parachutes), fished out of the water, and
re-used.

On a liquid fueled booster, the tanks are just tanks, so they have to deal
with considerably less pressure and can be made much lighter weight. On the
old Atlas ICBM (liquid fueled) the tanks were extremely lightweight. The
tanks were so thin and light they called them balloon tanks. They had to be
pressurized to several PSI on the ground or else they would collapse. If
you ever see an old Atlas ICBM on display, don't be surprised if it's
attached to an air compressor. ;-)

Jeff 

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