TRW-Built Pintle Rocket Engine Promises to Lower Launch Costs

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.

“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 —
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 NASA’s 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 vehicle’s 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 NASA’s Chandra
X-ray Observatory to the 10,000-pound thrust Delta and LMDE engines.

TRW Space & Electronics Group builds communications, scientific
and defense spacecraft for military, civil and commercial customers;
produces, integrates and tests payloads; develops advanced space
instruments; and integrates experiments into spacecraft. It is an
operating unit of TRW Inc., which provides advanced technology
products and services for global automotive, aerospace and information
systems markets. TRW’s Web site is www.trw.com.