During the 1990s two SR-71 Blackbird aircraft were used by NASA as testbeds for high-speed and high-altitude aeronautical research at Dryden. The aircraft included an SR-71A and SR-71B (the trainer version), loaned to NASA by the U.S. Air Force. Information from the LASRE experiment helped Lockheed Martin maximize its design for a future potential reusable launch vehicle. It gave Lockheed an understanding the performance of the X-33 lifting body and linear aerospike engine combination.
LASRE was a small, half-span model of a lifting body with eight thrust cells of an aerospike engine. The experiment, mounted on the back of an SR-71 aircraft, operated like a kind of "flying wind tunnel." The experiment focused on determining how a reusable launch vehicle's engine plume would affect the aerodynamics of its lifting body shape at specific altitudes and speeds reaching approximately 750 miles per hour. The interaction of the aerodynamic flow with the engine plume could create drag; design refinements look to minimize that interaction.
During the flight research project, the aircraft completed seven research flights. Two initial flights were used to determine the aerodynamic characteristics of the LASRE apparatus on the back of the aircraft. The first of those two flights occurred Oct. 31, 1997. 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 and a maximum altitude of 33,000 feet before landing at Edwards at 10:21 a.m. PST, successfully validating the SR-71/pod configuration.
Five follow-on flights focused on the experiment; two were used to cycle gaseous helium and liquid nitrogen through the experiment to check its plumbing system for leaks and to check engine operation characteristics. The first of these flights occurred March 4, 1998. 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.
During three more flights in the spring and summer of 1998, liquid oxygen was cycled through the engine. In addition, two engine hot firings were conducted on the ground.
It was decided not to do a final hot-fire flight test due to the liquid oxygen leaks in the test apparatus. The ground firings and the airborne cryogenic gas flow tests provided enough information to predict the hot gas effects of an aerospike engine firing during flight.
In 1990, after the Air Force formally retired the Blackbirds, NASA arranged to acquire two SR-71A models and the sole remaining SR-71B trainer for use as research aircraft. The following year, the SR-71B was used in tests of the Navy Radar Surveillance Technology Experimental Radar (RSTER) during a sortie over the Atlantic Ocean. The RSTER was an ultrahigh frequency sensor designed to detect high-flying missiles despite a high degree of radar clutter and jamming interference.
In another project, an SR-71A carried an Orbital Sciences Corporation frequency scanning experiment and the OSC F3SAT backup satellite, carried in passive mode to check pre-launch conditions. At extremely high altitudes, the airplane was an ideal platform for remote sensing technology experiments. Between October 1993 and October 1994, the aircraft carried several such packages.
In the spring of 1993, the SR-71A carried the Southwest Research Institute Ultraviolet Imaging System. The UV-sensitive charge-coupled device, combined with a telescope, was a prototype for a miniature astronomical lab designed for use on the space shuttle. That summer the airplane’s nose was equipped with a near-ultraviolet spectrometer for observation of volcanic gases in the UV spectrum. An upward-looking UV-sensitive video camera recorded a variety of celestial objects in wavelengths blocked from the view of ground-based astronomers. The Low Earth Orbit Experiment validated technology for ozone mapping sensors to be carried on the Russian Meteor-3 satellite.
Finally, a Dynamic Auroral Viewing Experiment provided data for the U.S. Navy.
The SR-71 also served as a testbed for an Optical Air Data System (OADS), a fiber optic device using laser technology to replace the pitot tube (airspeed probe) on high-performance aircraft. It used laser light instead of air pressure to produce airspeed and attitude reference data such as angle of attack and sideslip normally obtained with small tubes and vanes extending into the air stream or from tubes with flush openings on an aircraft's outer skin. The flights provided information on the presence of atmospheric particles at altitudes above 80,000 feet, where future hypersonic aircraft might be expected to operate. The system, known as a sheet-pair laser anemometer, projected six sheets of laser light from the underside of the airplane. As microscopic atmospheric particles passed between the beams, direction and speed were measured and processed into standard speed and attitude references. An earlier OADS data collection system was successfully tested at Dryden on an F-l04 testbed.
Under NASA's commercialization assistance program the SR-71 was used in the development of Motorola’s commercial satellite-based, instant wireless personal communications network, called IRIDIUM. During IRIDIUM development tests, the SR-71 acted as a surrogate satellite for transmitters and receivers on the ground.
The SR-71 also was used in a project for University of California-Los Angeles researchers investigating the ability of charged chlorine atoms to protect and rebuild Earth’s ozone layer.
In 1995, NASA crews flew a number of sonic boom research flights in support of the High-Speed Research Program. This was a NASA-wide program to develop technology for a supersonic passenger aircraft called the High-Speed Civil Transport. Researchers used the SR-71 to study ways of reducing sonic boom overpressures in the hope that such data could eventually lead to aircraft designs that would reduce peak overpressures and minimize the startling effect they produce on the ground.
The final major project for NASA’s SR-71 involved the Linear Aerospike SR-71 Experiment (Fig. 25). Technicians mounted a 41-foot-long flight test fixture, dubbed the “canoe” and capable of containing liquid rocket propellants, on top of the aircraft. It supported a 12-percent-scale, half-span model of an X-33 research vehicle – a prototype of a proposed space shuttle replacement – complete with a working linear aerospike engine with eight thrust cells. In this way the SR-71 served as a flying wind tunnel to validate ground-based wind-tunnel data and computer-generated predictions. Although the X-33 project was cancelled in 1998, the experiment provided researchers with information that may help predict how operation of aerospike engines at altitude will affect the aerodynamics of a future reusable launch vehicle.
The NASA/Lockheed Martin Linear Aerospike SR-71 Experiment (LASRE) concluded its flight operations phase in November 1998.