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The SR-71, unofficially known as the “Blackbird,” is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft. The first flight of an SR-71 took place on Dec. 22, 1964, and the first SR-71 to enter service was delivered to the 4200th (later 9th) Strategic Reconnaissance Wing at Beale Air Force Base, Calif., in January 1966.
Throughout its nearly 24-year career, the SR-71 remained the world’s fastest and highest-flying operational aircraft. From 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour.
NASA crews flew four Lockheed SR-71 airplanes during the 1990s. According to NASA, Two were used for research and two to support Air Force reactivation of the SR-71 for reconnaissance missions. Although the Air Force retired the Blackbirds in 1990, Congress reinstated funding for additional flights several years later.
SR-71A (61-7980/NASA 844) arrived at Dryden on Feb. 15, 1990. It was placed into storage until 1992 and served as a research platform until its final flight on Oct. 9, 1999. SR-71A (61-7971/NASA 832) arrived at Dryden on March 19, 1990, but was returned to Air Force inventory as the first aircraft was reactivated in 1995. Along with SR-71A (61-7967), it was flown by NASA crews in support of the Air Force program. SR-71B (61-7956/NASA 831) arrived at Dryden on July 25, 1991, and served as a research platform as well as for crew training and proficiency until October 1997.
As told by Scott Lowther in the book Origins and Evolution Lockheed SR-71 Blackbird, for a brief moment, there was some interest in using the SR-71 to compete with the National Aero Space Plane (NASP) programme. This ambitious-as it turned out, overly ambitious – programme called for the development of a single stage to orbit aircraft powered largely by scramjet engines. The claim was that an airbreathing vehicle able to launch from and land at airport runways would prove more economical to operate as a space launcher than conventional expendable rockets. History has shown the difficulty of` developing engines that work reliably and profitably with supersonic airflows to be extreme.
In lieu of the incredibly expensive and risky programme to develop the full-scale, full-speed (up to Mach 25) NASP scramjet, in 1992 NASA-Ames – otherwise not a major player in the NASP programme – proposed the development of the ‘HALO’ (originally the High-Altitude Launch Option, later the Hypersonic Air Launch Option) research vehicle. This would be a subscale NASP-like configuration complete with scramjet engines and provisions for a crew of one. The idea seems to have lasted for a couple of years, but detailed design work has not come to light. Information on the HALO vehicle is vague and contradictory, indicating that over time it changed considerably.
The HALO vehicle was, in general, a relatively slim flat-bottomed lifting body with an underslung rectangular scramjet module. The long sloping underside of the forward fuselage served as an inlet compression ramp. At the chopped-off rear of the fuselage was a submerged linear aerospike rocket engine, needed to boost the vehicle up to a speed where the scramjet could operate effectively.
The NASP vehicle is rarely depicted with such an engine, but it nevertheless would have needed rockets for the final circularization into orbit. A cockpit for a single pilot would be fitted, likely somewhat well back on the fuselage due to the relatively thin nose
The HALO would be carried to altitude on the back of an SR-71 in a manner similar to the D-21 atop the M-21. or like the earlier Lockheed study of the HT-4 drone carried atop the SR-71. Launch of the HALO would occur at Mach 3 and 80,000ft, followed by a rocket-powered climb to Mach 9 and somewhere over 140,000ft. Following that, the craft would fly under scramjet power for two minutes, descending to around 100,000ft while accelerating to Mach 10. The pilot would then glide the vehicle to a horizontal landing in a similar manner to the X-15.
The purpose was not to aid the NASP programme, but to supplant it. By 1992, NASP was encountering serious problems with both technology and budget and the rise of a competing system only made the problems worse, NASP was finally cancelled in 1993, but HALO hung on at least into 1994.
Origins and Evolution Lockheed SR-71 Blackbird is published by Mortons Books and is available to order here.
Photo credit: Mortons Books and Unknown
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