NASA Dryden Press Release 98-08
March 5, 1998

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

During a cold flow flight, gaseous helium and liquid nitrogen are cycled through the linear aerospike engine to check the engine's plumbing system for leaks and to check the engine operating characterisitcs. Cold-flow tests must be accomplished successfully before firing the rocket engine experiment in flight.

The SR-71 took off at 10:16 a.m. PST. The aircraft flew for one hour and fifty-seven minutes, reaching a maximum speed of Mach 1.58 before landing at Edwards at 12:13 p.m. PST.

"I think all in all we had a good mission today," Dryden LASRE Project Manager Dave Lux said.

Flight crew member Bob Meyer agreed, saying the crew "thought it was a really good flight." Dryden Research Pilot Ed Schneider piloted the SR-71 during the mission.

Lockheed Martin LASRE Project Manager Carl Meade added, "We are extremely pleased with today's results. This will help pave the way for the first in-flight engine data-collection flight of the LASRE." The first engine data-collection flight currently is scheduled for sometime in April.

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.

The engine data-collection 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.

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. 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.