NASA Shifts SLI Funds to Kerosene Engines

Frank Morring, Jr. / Washington

NASA's Space Launch Initiative (SU) will not continue funding the hydrogen-fueled rocket engine it has had under development by Pratt & Whitney and Aerojet, opting instead to push development of kerosene-fueled rockets for a future reusable launch vehicle (RLV).

The SLI program office will have spent about $57 million on the Co-optimized Booster for Reusable Applications (Co- bra) engine at the end of its first contract option Sept. 30, and does not plan to extend the contract. Boeing's Rocketdyne unit is also developing a hydrogen-fueled rocket engine for SLI, the 650,000-lb. sea- level thrust RS-83, under a contract that runs through May 2003, and the SLI propulsion office has not decided whether it will extend that contract.

Architecture studies completed since the original Cobra and RS-83 contracts were awarded last year have steered the SLI program toward a liquid oxygen/ hydrocarbon-fuel first stage engine for a next-generation RLV; in part because the fuel can also be used for air-breathing jets to power fly-back boosters on their return to the launch site (AW&ST Apr. 1, p. 28).

The SLI propulsion office at NASA's Marshall Spaceflight Center considers hydrocarbon engine technology less mature than engines using LOX and liquid hydrogen, and wants to use its funds to advance the state of the art in hydrocarbon rocket propulsion.

"We feel like we're going to need more time to work the risk mitigation on that engine, and so we feel like we can delay the hydrogen work," said Gary Lyles, SLI propulsion project manager. "Because Cobra's option came up now, we felt like we needed to go ahead and not execute that option."

By terminating the project at the $57-million mark, the SLI office will retain about $68 million that was originally programmed for the Cobra engine. Lyles said his office hopes to use some of that money to step up testing and other risk mitigation work needed to mature 'hydrocarbon rocket engine technology. Combustion stability in large kerosene engines has been a problem since the days of the F-I engines used on the first stage of the Saturn V Moon rocket, and Lyles said the program would like to conduct large-scale injector tests to work the problem.

"We don't really have good analytical tools to design around that problem, so it requires that we do testing on injectors, and that we do testing at pretty large scale, almost full scale," Lyles said.

Other problems in running a reusable hydrocarbon engine include preventing coking, the residue deposits left when kerosene used to cool engine components is overheated; keeping the engine size as small as possible for ease of integration into reusable launch vehicles, and finding materials able to stand up to repeated use in the oxygen-rich turbine environment without coatings that can chip and wear.

"The biggest thing we look at in the end may be reusability," Lyles said. "The world has never built reusable hydrocarbon engines."

The SLI propulsion office has support- ed work on two LOX/kerosene engines under its original propulsion plan, the Rocketdyne RS-84 and the TRW TRI 07. In addition, P&W and Aerojet have proposed Russian-derived hydrocarbon engines (AW&ST Apr. 29, p. 60). The Rocketdyne engine uses special manifolds spaced to prevent cooling kerosene in the combustion chamber and engine nozzle walls from heating to the coking point, and in some cases to injects kerosene directly into the thrust chamber for additional cooling. TRW's entry uses a duct-cooled main combustion chamber instead of cooling channels in the walls, and incorporates special materials designed to prevent. coking.

Both engines adopt the staged combustion cycle for greater efficiency than was provided by the F-I engines, which used a gas generator cycle. Higher chamber pressures -- 2,600 psi. instead of 965 psi. on the F-1 -- allow smaller engines, although at I. I-million-lb. thrust the SLI variants would approach the 1.5-million- lb. thrust generated by the Saturn engines.

The Cobra engine, a single fuel-rich preburner staged combustion engine rated at 600,000-lb. thrust in vacuum, took the Space Shuttle Main Engine (SSME) as its starting point. It used the advanced turbopumps P&W developed for SSME and added P&W integrated vehicle health management technology from air-breathing jet engine programs and advanced fabrication technologies supplied by Aerojet. The Cobra would mount its turbopumps in parallel, like the SSME, while the RS-83 would carry newly developed turbopumps mounted in series.

In June, the Cobra engine passed its preliminary design review, marking the point when an engine design is about 50% complete. With the termination of the contract, all deliverable data, hardware and long-lead materials that NASA purchased will become the property of the space agency, while the contractors will retain any proprietary data.

Aerojet expects a small reduction in force at its Sacramento, Calif, facility as a result of the contract termination, while Pratt was still assessing the impact on its engineering staff last week. Lyles said that while the first-stage emphasis at SLI has shifted to hydrocarbons-a position it shares with the U.S. military-there still will be work on hydrogen-fueled engines under the NASA launch technology effort.