SR-71 takeoff with afterburner showing shock diamonds in exhaust
Two SR-71 aircraft were used by NASA as testbeds for high speed, high altitude aeronautical research. The aircraft, an SR-71A and an SR-71B pilot trainer aircraft were based at NASA's Dryden Flight Research Center, Edwards, California.
Developed for the USAF as reconnaissance aircraft more than 30 years ago, SR-71s are still the world's fastest and highest-flying piloted aircraft. The aircraft flew at more than 2200 mph (Mach 3+ or more than three times the speed of sound) and at altitudes over 85,000 feet. As research platforms, the aircraft could cruise at Mach 3 for more than one hour. For thermal experiments, this produced heat soak temperatures of over 600 degrees (F). This operating environment made the aircraft excellent platforms to carry out research and experiments in a variety of areas - aerodynamics, propulsion, structures, thermal protection materials, high-speed and high-temperature instrumentation, atmospheric studies, and sonic boom characterization.
One of the first major experiments flown in the NASA SR-71 program was a laser air data collection system. 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.
The first of a series of flights using the SR-71 as a science camera platform for NASA's Jet Propulsion Laboratory was flown in March 1993. From the nosebay of the aircraft, an upward-looking ultraviolet video camera studied a variety of celestial objects in wavelengths that are blocked to ground-based astronomers.
SR-71 in-flight view from tanker
The SR-71 was also used in a program to study ways of reducing sonic boom overpressures that are heard on the ground much like sharp thunderclaps when an aircraft exceeds the speed of sound. Data from the Sonic Boom Mitigation Study could eventually lead to aircraft designs that would reduce the "peak" of sonic booms and minimize the startle affect they produce on the ground. One of Dryden's SR-71s was used for the Linear Aerospike SR Experiment, or LASRE, in which the unique aerospike engine developed for the X-33 Reusable Launch Vehicle was mounted on the back of the SR-71.
Dryden has a decade of past experience at sustained speeds above Mach 3. Two YF-12 aircraft were flown at the facility between December 1969 and November 1979 in a joint NASA/USAF program to learn more about the capabilities and limitations of high speed, high altitude flight. The YF-12s were prototypes of a planned interceptor aircraft based on a design that later evolved into the SR-71 reconnaissance aircraft.
The aircraft were 107.4 feet (32.73 m) long, have a wing span of 55.6 feet (16.94 m), and are l8.5 feet (5.63 m) high (ground to the top of the rudders when parked). Gross takeoff weight was about 140,000 pounds (52,253 kg), including a fuel weight of 80,000 pounds (29,859 kg). The airframes are built almost entirely of titanium and titanium alloys to withstand heat generated by sustained Mach 3 flight. Aerodynamic control surfaces consist of all-moving vertical tail surfaces above each engine nacelle, ailerons on the outer wings, and elevators on the trailing edges between the engine exhaust nozzles.
The two SR-71s at Dryden were assigned the following NASA tail numbers: NASA 844 (A model), military serial 64-17980, manufactured in July 1967, and NASA 831 (B model), military serial 61-7956, manufactured in September 1965. From 1991 through 1994, Dryden also had another "A" model, NASA 832, military serial 61-7971, manufactured in October 1966. This aircraft was returned to the USAF inventory and was the first aircraft reactivated for USAF reconnaissance purposes in 1995.