Asri-unix.1112
net.space
utcsrgv!utzoo!decvax!ucbvax!ARPAVAX:C70:sri-unix!DIETZ@USC-ECL
Sun Mar 28 16:18:21 1982
Advanced Rockets and SSTO's
I went to an interesting presentation last night about a new rocket
idea called the Dual Expander rocket engine. The idea is this: most
of the mass of propellant in a rocket is burned during the first
parts of the launch. As it turns out, if you want to build a single stage
to orbit vehicle the fuel burned during the first part should NOT
be chosen for high exhaust velocity, but rather for high propellant
density. Specifically, we should use hydrocarbons (like propane, methane
or kerosene) instead of hydrogen.
The dual expander rocket engine burns both hydrocarbons (propane) and
hydrogen. It is essentially an engine within an engine. The interior
engine burns propane and LOX during the first part of the launch with
a chamber pressure of 6000 psia. It is surrounded by an annular combustion
chamber where hydrogen and LOX are burned. This outer chamber has a
smaller aperature than the space shuttle main engine, so a smaller
nozzle is needed. When the center engine is shut down it generates
far less thrust than the SSME, but at that point you don't need much thrust.
The eignine has a top thrust of 1/2 of the SSME, but weighs 1/3 as much.
The speaker presented several designs using the engines. The first
is an upgraded shuttle. The SRB's are removed, and the main tank is
enlarged to include a propane tank and extra LH and LOX. On the bottom
of the tank goes a cluster of (eight?) dual expander engines. Both
the tank and the orbiter are placed in a stable orbit. The engines are
removed from the tank and returned inside the shuttle. If you want
a real heavy lift vehicle, put the SRB's back on. I forget the exact
figures but this thing lifts well over 100,000 lbs. of payload. And
you have a tank in orbit to play with.
A one man Air Force shuttle was also described. It is much smaller
than the space shuttle. Depending on the exact design, it can be launched
from a C5A or from the ground. It uses two dual expander engines
and strap on propane tanks that get left in orbit.
Next, several commercial SSTO's. Three designs were given, the smallest
smaller than the space shuttle, the largest weighing 10,000,000 lb.
and having 29 (!) engines.
The speaker also showed how you can take the proposed airforce shuttle,
put it on an upgraded space shuttle tank and get a vehicle capable
of getting to geosynchronous orbit and back again. Another proposed
design used LEO refueling from an ordinary shuttle.
The last and most practical design is a disposable SSTO unmanned booster.
It has two dual expanders. On top goes a second stage that propels the
payload to geosynchronous orbit. It could carry over 6000 lbs. of payload.
The kicker is this: the first stage is ~14 feet in diameter by 50 some
odd feet long. These numbers should ring a bell, because the shuttle
cargo bay is 15'x60', making this a "fully reusable disposable". Final
note on this thing: it can be air-launched from the back of a 747! This
would avoid dynamic pressure problems. Launch procedure involves putting
the 747 into a 45 degree climb at 30,000 feet, igniting the rocket and
pulling negative g's to get away. Boeing is examining putting a SSME
in the tail of a 747 (!) to get it higher. The launch altitude then
becomes something like 50,000 or 60,000 feet. This last idea has been
looked at by SAC already; in the 60's they considered putting a Titan
engine in the tail of a B52 to get it away from the field quickly: said
vehicle could be at 30,000 feet 30 miles from the runway in 1 minute!
I hope they get to develope the engine. It uses no really new
technology. The speaker claimed it could be developed in 4-5 years at
a cost of $400M (1980). He works for Aerojet (the company
responsible for this thing) so he isn't unbiased.
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