The SR-71 Blackbird
A second NASA effort in the 1990s employed several SR-71 aircraft as high-speed, high-altitude laboratories to conduct a variety of scientific experiments.
One of the first major experiments flown on the NASA SR-71 involved a laser air-data sensor. The sensor used laser light instead of air pressure to generate airspeed and attitude data such as angle-of-attack and sideslip, data normally obtained with small tubes and vanes extending into the airstream or from tubes with flush openings on an aircraft's outer skin. These flights also provided information on the presence of atmospheric particles at altitudes above 80,000 feet, where future hypersonic aircraft will operate. The system used six sheets of laser light projected from the bottom of the airplane. As microscopic-size atmospheric particles passed between the two beams, direction and speed were measured and processed into standard speed and attitude references. An earlier laser air-data measurement system was successfully tested at Dryden on a modified F-l04 testbed aircraft.
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