TRW Inc. has taken a huge stride toward providing more affordable access to space with the successful initial static-fire testing of a low-cost booster engine based on TRW's pintle injection technology.

The 650,000-pound thrust Low Cost Pintle Engine (LCPE), one of the largest liquid rocket engines built since Saturn F-1 engines powered Apollo program flights in the 1970s, was designed as a simple, easy-to-manufacture, low-cost engine. The LCPE has parts made from common steel alloys using standard industrial fabrication techniques, employs ablative cooling techniques instead of more expensive regenerative cooling, and features the least complex type of rocket propellant injector -- a single element coaxial pintle injector.

Engine test firing. Photo: TRW

"Most engines are designed for maximum performance and minimum weight, but we deliberately set out to develop an engine that minimizes cost while retaining excellent performance," said Al Frew, vice president and general manager, TRW Space & Technology Division. "We believe this engine will cost 50 to 75 percent less than comparable liquid hydrogen boosters. By reducing engine costs, which make up almost half of the cost of a launch vehicle, we will reduce the cost of launch vehicles and access to space for government and commercial customers."

The LCPE was subjected this summer to hot fire testing at 100 percent of its rated thrust as well as at a 65 percent throttle condition at NASA's John C. Stennis Space Center in Mississippi. TRW changed the pintle injector configuration three times during testing to explore the engine's performance envelope; engineers also replaced the ablative chamber once while the engine was on the test stand æ demonstrating the LCPE's ease of operation.

"The LCPE has demonstrated nominal performance and absolute combustion stability throughout its testing," said Kathy Gavitt, TRW's LCPE program manager. "This testing is an important first step in validating that a low-cost pintle engine can substantially lower the cost of future launch vehicles."

Engine testing is planned to continue throughout the year under a cooperative agreement between TRW and NASAšs Marshall Space Flight Center.

The key element of the LCPE's design is its single element coaxial pintle injector, used to introduce propellants into the combustion chamber. TRW has used this design in nearly all of its bipropellant liquid rocket engines. This includes the Lunar Module Descent Engine (LMDE) which safely landed 12 astronauts on the lunar surface between 1969 and 1972 and was critical in the rescue of Apollo 13.

Other notable features of the LCPE are:

• Scalability. The LCPE is scalable over a range of thrust levels and propellant combinations. It can be readily adapted to a wide range of launch vehicles, from the Bantam Lifter class (about 200 pounds to low-Earth orbit) to Heavy Weight Lifter class (about 200,000 pounds to low-Earth orbit). The LCPE can power the first stage of an EELV-class, multistage launch vehicle, and scaled down versions can easily be used for the vehiclešs second stage.
• Combustion Stability. The LCPE is inherently stable over a wide range of operating conditions due to the unique injection and combustion flow fields created by the pintle injector.
• Size. Incorporates the second largest rocket combustion chamber ever built, with an outside diameter of 68 inches.
• Simplicity. A complete pintle injector contains only five parts (excluding seals and attachment nuts, bolts and washers).
• Throttling Ability. LCPE has already demonstrated its ability to operate at a 65 percent throttle condition. Moveable pintle injector attributes include deep throttle capability, such as the LMDE 10:1 throttling engine.

TRW has tested more than 50 different pintle injector engines, using more than 25 different propellant combinations with complete combustion stability and no need for acoustic cavities or baffles. Previously, pintle injector engines were successfully tested with liquid hydrogen and liquid oxygen at thrust levels of 16,000 and 40,000 pounds. TRW has flown more than 140 engines ranging in size from the 100-pound thrust liquid apogee engine used on NASAšs Chandra X-ray Observatory to the 10,000-pound thrust Delta and LMDE engines.