NASA News Release 97-41
October 31, 1997

A NASA SR-71 today successfully completed its first flight as part of the NASA/Rocketdyne/ Lockheed Martin Linear Aerospike SR-71 Experiment (LASRE) at NASA´s Dryden Flight Research Center, Edwards, Calif.

The SR-71 took off at 8:31 a.m. PST. The aircraft flew for one hour and fifty minutes, reaching a maximum speed of Mach 1.2 before landing at Edwards at 10:21 a.m. PST, successfully validating the SR-71/linear aerospike configuration.

"We had an excellent flight," Dryden LASRE Project Manager Dave Lux said. "Everything went just as we expected."

"For a first flight, this is about as good as they come," Dryden Center Director Ken Szalai said.

Lockheed Martin LASRE Project Manager Carl Meade added, "We are extremely pleased for the whole team."

Linear Aerospike rocket engines are going to power the X-33 Advanced Technology Demonstrator, scheduled to fly in 1999.

LASRE is designed to gather data on the aerospike´s exhaust plume as it travels through the transonic region of flight. Linear aerospike rocket engines have been laboratory and ground tested many times over the past thirty years, but have never flown until now.

LASRE is a one-tenth-scale, half-span model of the X-33. The model contains eight 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.

This flight is the first in a series of ground-based and in-flight 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 Research Laboratory Propulsion Directorate, formerly Phillips Laboratory.

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 around 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 modern 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 its 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.