English: Dryden's SR-71B, NASA 831, slices across the snowy southern Sierra Nevada Mountains of California after being refueled by an Air Force Flight Test Center tanker during a recent flight. The Mach 3 aircraft are being flown by the Dryden Flight Research Center, Edwards, California as testbeds for high-speed, high-altitude aeronautical research. Capable of flying more than 2200 mph and at altitudes of over 85,000 feet, they are excellent platforms for research and experiments in aerodynamics, propulsion, structures, thermal protection materials, atmospheric studies, and sonic boom characterization.