Re: Spaceship One in perspective

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

Date: Wed, 30 Jun 2004 14:00:02 -0400

"Neil Gerace" <geracen@iinet.net.au> wrote in message
news:40e2f1cc$0$24751$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
>
> If you want to compare apples with apples, you could start by making your
> liquid-fuelled rocket reusable, and then see if it's still lighter than
the
> SRB.

For a large rocket stage, liquid fuel means your dry mass can be far lighter
than with solids, which means your recovery equipment (e.g. parachutes or
wings) may not need to be as big.

Furthermore, with upper stages, this also means that you end up with a
large, light structure you need to get back to earth. Because it's large
and light, reentry heating loads are far lower, so your TPS doesn't need to
be as heavy or expensive.

Lastly, it's debatable if the reusing the shuttle SRB's actually saves much
money. The cost to recover, clean, and inspect the SRB segments isn't
trivial. With lighter liquid fuel tanks, you can design things like
fly-back lower stages where recovery costs are low and refueling costs are
even lower (since you don't have to clean out a solid's huge combustion
chamber out before you refill it).

One last thing, the cost to fill an SRB isn't cheap either. The segments of
the shuttle SRB's are cast in pairs so they have close to the same burn
rate. This process is done at "the factory" because it's complex and
potentially dangerous. With liquid fueled stages, you can leave them empty
until the vehicle reaches the pad. This lowers costs in major and minor
ways, like making operations in the VAB easier.

Jeff 

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