Double the performance? I might believe 10%-20%. The men who designed
the SSMEs are all dead or retired. Their hundreds of years of combined
experience and working knowledge allowed them to strike a rather
delicate balance between efficiency and reliability, the latter being
somewhat important in a man-rated vehicle. NASA has done zip to advance
their knowledge base or to train the next generation of propulsion
engineers and scientists, so the achievements of those old Germans will
likely stand for quite some time.

NASA needs to move away from chemical propulsion technology. O'Keefe
tried to push in that direction and look where it got him. The "new"
guy, Griffin, is an insider who remembers Apollo with great fondness. So
now the taxpayers will get Apollo V2.0. There will be one big difference
though, the money will be spent at a much higher rate, and no measurable
performance goals will be allowed in this go-round.

Rich wrote:
When you think of future rocket technology, you probably think of ion
propulsion, antimatter engines and other exotic concepts. Not so fast!

Image: Robert Goddard and a 1920s-vintage liquid-fueled rocket.

The final chapter in traditional liquid-fueled rockets has yet to be
written. Research is underway into a new generation of liquid-fueled
rocket designs that could double performance over today's designs
while also improving reliability.

Liquid-fueled rockets have been around for a long time: The first
liquid-powered launch was performed in 1926 by Robert H. Goddard. That
simple rocket produced roughly 20 pounds of thrust, enough to carry it
about 40 feet into the air. Since then, designs have become
sophisticated and powerful. The space shuttle's three liquid-fueled
onboard engines, for instance, can exert more than 1.5 million pounds
of combined thrust en route to Earth orbit.

You might assume that, by now, every conceivable refinement in
liquid-fueled rocket designs must have been made. You'd be wrong. It
turns out there's room for improvement.

Led by the US Air Force, a group consisting of NASA, the Department of
Defense, and several industry partners are working on better engine
designs. Their program is called Integrated High Payoff Rocket
Propulsion Technologies, and they are looking at many possible
improvements. One of the most promising so far is a new scheme for
fuel flow:

The basic idea behind a liquid-fueled rocket is rather simple. A fuel
and an oxidizer, both in liquid form, are fed into a combustion
chamber and ignited. For example, the shuttle uses liquid hydrogen as
its fuel and liquid oxygen as the oxidizer. The hot gases produced by
the combustion escape rapidly through the cone-shaped nozzle, thus
producing thrust.

The details, of course, are much more complicated. For one, both the
liquid fuel and the oxidizer must be fed into the chamber very rapidly
and under great pressure. The shuttle's main engines would drain a
swimming pool full of fuel in only 25 seconds!

This gushing torrent of fuel is driven by a turbopump. To power the
turbopump, a small amount of fuel is "preburned", thus generating hot
gases that drive the turbopump, which in turn pumps the rest of the
fuel into the main combustion chamber. A similar process is used to
pump the oxidizer.

Today's liquid-fueled rockets send only a small amount of fuel and
oxidizer through the preburners. The bulk flows directly to the main
combustion chamber, skipping the preburners entirely.

One of many innovations being tested by the Air Force and NASA is to
send all of the fuel and oxidizer through their respective preburners.
Only a small amount is consumed there--just enough to run the turbos;
the rest flows through to the combustion chamber.

This "full-flow staged cycle" design has an important advantage: with
more mass passing through the turbine that drives the turbopump, the
turbopump is driven harder, thus reaching higher pressures. Higher
pressures equal greater performance from the rocket.

Such a design has never been used in a liquid-fueled rocket in the
U.S. before, according to Gary Genge at NASA's Marshall Space Flight
Center. Genge is the Deputy Project Manager for the Integrated
Powerhead Demonstrator (IPD)--a test-engine for these concepts.

"These designs we're exploring could boost performance in many ways,"
says Genge. "We're hoping for better fuel efficiency, higher
thrust-to-weight ratio, improved reliability--all at a lower cost."

"At this phase of the project, however, we're just trying to get this
alternate flow pattern working correctly," he notes.

Already they've achieved one key goal: a cooler-running engine.
"Turbopumps using traditional flow patterns can heat up to 1800 C,"
says Genge. That's a lot of thermal stress on the engine. The "full
flow" turbopump is cooler, because with more mass running through it,
lower temperatures can be used and still achieve good performance.
"We've lowered the temperature by several hundred degrees," he says.

IPD is meant only as a testbed for new ideas, notes Genge. The
demonstrator itself will never fly to space. But if the project is
successful, some of IPD's improvements could find their way into the
launch vehicles of the future.

Almost a hundred years and thousands of launches after Goddard, the
best liquid-fueled rockets may be yet to come.

Source: Science@NASA (by Patrick L. Barry)