How to Build a Better Rocket

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.

A rendering of the Integrated Powerhead Demonstrator, showing its innovative plumbing for routing fuel and oxidizer 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.