From: Doug Jones (random@qnet.com)
Date: Mon Jun 28 1999 - 16:12:25 MDT
S.J. Van Sickle wrote:
>
> Assuming you couldn't use any RR proprietary stuff, how about
> the little positive displacement pump engines Lawrence-Livermore
> worked on? You could build a slick little 2 person or one
> person/one experiment rack vtvl for a lot less than even RR
> is spending for the scientific and barnstorming market. Or even
> just sell the engines to homebuilt aircraft
> and HPR enthusiasts. Zoom!!!
>
> steve
Actually, for modest delta-v high acceleration missions,
pressure-fed combustors with filament wound tanks win over any pump
system. The tanks give you a *very* strong structural keel, and
with appropriate choice of propellants, the fuel & oxidizer
pressurize themselves (such as ethane and nitrous oxide at room
temperature). For a second stage orbiter, the remaining cold dense
vapor in the tanks is used for orbital maneuvering- you literally
run on fumes :)
Lower pressure engines are easier to regeneratively or ablatively
cool, although they have lower performance in the atmosphere. In
vaccum, they do as well as higher pressure engines, but are a bit
bulky (1/4 pressure needs 2x nozzle diameter for same thrust).
Ignition sequence timing is simpler, since you only have to light
the chamber, no preburner or gas generator needed.
I see two optima for launch vehicles: SSTO with very high
performance topping-cycle engines, or pressure fed two stage.
Systems complexity is what's expensive. Single stage gets rid of
stage integration and separation, pressure fed gets rid of pumps and
can integrate main, reaction control, and orbital maneuvering
thrusters into a single system.
As for barnstorming, there is some very real interest in a flying
Me-163 replica... now *that* would be a fun project.
-- Doug Jones, Freelance Rocket Plumber
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