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, CA.
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.
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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.
https://www.nasa.gov/centers/dryden/history/pastprojects/SR71/index.htmlEarly 90's NASA SR-71 15 min video.
http://www.youtube.com/watch?v=WOQncsVloow&ab_channel=LogicEarthThe Blackbird project was finally (and permanently) retired in 1998. Two last flyable Blackbirds were given to NASA which flew until 1999. All but two SR-71’s (the ones given to NASA) are now in museums for people to see.
