NASA News Release 97-34
August 28, 1997
LINEAR AEROSPIKE EXPERIMENT MOUNTED ON SR-71 IN PREPARATION FOR FLIGHT
The Linear Acrospike SR-71 Experiment was mounted on a NASA SR-71 aircraft Aug.
26, at the NASA Dryden Flight Research Center, Edwards, Calif., in preparation for
the experiment's first flight, currently scheduled for sometime in September.
Linear Aerospike rocket engines will power NASA's X-33 Advanced Technology Demonstrator,
scheduled to fly in 1999.
The NASA/Rocketdyne/Lockheed Martin Linear Aerospike SR-71 Experiment, known
as LASRE, is designed to gather data on the aerospike's exhaust plume as it travels
through the transonic region of flight (just below to just above Mach 1). Linear
aerospike rocket engines have been laboratory and ground tested many times during
the past thirty years, but have never flown.
"The LASRE experiment has gone through a long and arduous development program
and is finally ready for flight," Dryden LASRE Project Manager Dave Lux said.
"The installation of the Pod on the SR-71 signals the light at the end of the
tunnel. We are very excited about finally coming to the point of obtaining the flight-research
data."
Carl Meade, Lockheed Martin LASRE Project Manager added, "This marks an
important milestone on LASRE. We have met and solved some tough challenges on the
program, and now we are nearly ready to fly. Each team member can take pride in our
accomplishments on this unique program."
LASRE is a one-tenth-scale, half-span model of the X-33. The model contains four
thrust cells of an aerospike engine and is mounted on a housing known as the "canoe,"
which contains the gaseous hydrogen, helium and instrumentation gear. The model,
engine and canoe together are called the "pod." The entire pod is 41 feet
in length and weighs 14,300 pounds.
The goal of the first flight, called an "aero" flight, is to evaluate
the SR-71-pod configuration. It is an aerodynamic data-collection flight and the
rocket engine will not be ignited. The flight will be used to gather valuable information
about the stability and control, performance, aerodynamic characteristics and structural
integrity of the aircraft-pod configuration as the SR-71 approaches and passes Mach
1.
The aero flight will be the first step in a series of in-flight and ground-based
qualifications tests. Following these tests, a decision will be made to proceed to
data-collection flights of the linear aerospike or to pursue more ground testing
at the U. S. Air Force's Phillips Laboratory's Propulsion Directorate facilities
at Edwards. Earlier this year, LASRE completed a series of ground tests at the Propulsion
Directorate's facilities validating the model's rocket-fuel plumbing and ignition
system.
A "typical" LASRE data-collection flight will consist of the SR-71
taking off to rendezvous with a tanker aircraft for aerial refueling. Then, the SR-71
with the piggyback LASRE pod will climb up to a predetermined altitude between 20
and 80 thousand feet. The linear aerospike will then be fired for the collection
of in-flight data on the performance of the engine. The LASRE pod carries enough
fuel for one aerospike rocket engine firing per flight, which will last two to three
seconds.
The flight research missions will measure the rocket engine's performance, from
subsonic speeds up to Mach 3, or approximately 2,200 miles per hour. Among the important
flight test points scheduled will be the data gathered as the SR-71 passes through
the so-called transonic region, from roughly Mach 0.8 to Mach 1.2, or approximately
750 miles per hour. The flight research missions will be used to gather accurate
data on the interaction of the X-33 model's airflow with that of the linear aerospike
engine and it's exhaust plume. This data will also help determine the efficiency
of the rocket engine. The aerospike engine is expected to produce approximately 7,000
pounds of thrust. The total cost of the LASRE program is approximately $20 million.
Linear Aerospike Engine Technology
Linear aerospike rocket engines have been in existence for more than thirty years.
Based on a concept developed by the Air Force's Propulsion Directorate in the early
1960s, Rocketdyne, now Boeing North American - Rocketdyne, developed the technology
for both linear and annular aerospike engines during the mid-1960s, ground testing
various designs into the 1970s. Rocketdyne proposed the aerospike engine for use
on the Space Shuttle, but the engine was turned down because the technology was considered
too immature at the time. Since then, Rocketdyne has accomplished 73 laboratory and
ground test firings, with over 4,000 seconds of operation of this type engine. Rocketdyne
has spent over $500 million over the years to test and improve aerospike engine technology.
Recent improvements funded by the Air Force in the early 1990s made it possible to
improve the manufacturing of aerospike engine thrust cells, while modem performance
sensors and monitoring controls enable split-second engine control.
The linear aerospike engine is very similar to normal rocket engines in it's
plumbing and accessories, utilizing similar components, such as turbopumps. However,
one of the major differences, and the most notable, is the absence of a bell-shaped
nozzle. The linear aerospike engine uses the atmosphere as part of it's nozzle, with
the surrounding airflow containing the rocket's exhaust plume. This keeps the engine
at optimum performance and efficiency along the entire trajectory of ascent to orbit.
Traditional rocket engines cannot compensate for atmospheric changes, from low altitude
and high atmospheric pressure, to high altitude and low atmospheric pressure. So,
they are designed for a particular performance range in an effort to get the best
performance from them.
Another major difference is that linear aerospike engines are 75 percent smaller
than normal rocket engines of comparable thrust. The smaller design means less engine
weight and less engine support structure required, which allows for lighter spacecraft.
This will result in lower cost to launch a vehicle into orbit.
X-33 and the Reusable Launch Vehicle Program
The X-33 is a technology demonstrator for a Single-Stage-To-Orbit (SSTO) Reusable
Launch Vehicle (RLV). The RLV technology program is a cooperative agreement between
NASA and industry. The goal of the RLV technology program is to enable significant
reductions in the cost of access to space, and to promote the creation and delivery
of new space services and other activities that will improve U.S. economic competitiveness.
The program implements the National Space Transportation Policy, which is designed
to accelerate the development of new launch technologies and concepts to contribute
to the continuing commercialization of the national space launch industry.
The RLV program consists of both the X-33 and the X-34 technology demonstrators.
The smaller X-34 will test the feasibility of launching small commercial and scientific
payloads aboard a reusable rocket.
NOTES:
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