The SR-71 Blackbird served NASA as a high-speed, high-altitude research aircraft capable of flying above 85,000 feet at cruising speeds up to Mach 3.32, or 2,193 miles per hour. Built in 1967, this SR-71A was the final Blackbird built and the last to fly. Constructed primarily from titanium alloys to withstand the high temperatures caused by aerodynamic heating, it also used special composite materials on the edges of the wings, the fuselage, and other areas to reduce radar cross-section. Before its transfer to NASA in 1990, Air Force crews flew it on operational reconnaissance missions over Southeast Asia and the Middle East. At NASA, it carried scientific experiments supporting spacecraft and aircraft development, astronomy, environmental monitoring, and sonic boom research. By its final flight on October 9, 1999, it had completed 734 flights, including 678 for the Air Force and 56 research missions for NASA, and had accumulated 2,353.6 flight hours. The SR-71 was powered by two Pratt and Whitney J58 turbojet engines, each producing 32,500 pounds of thrust. Originally designed for a U.S. Navy requirement, the J58 was later developed for the A-12, YF-12, and SR-71 after cancellation of its intended airframe. Its variable geometry inlet diffuser and complex bleed bypass system allowed efficient operation between Mach 2.0 and 3.2 by controlling the shockwave inside the inlet and routing some air past the turbine section directly to the afterburner, enabling turbo-ramjet operation. During cruise, parts of the engine reached temperatures as high as 3,200 degrees Fahrenheit.