Smithsonian Air and Space Museum / The X 15 was a rocket powered aircraft developed by North American Aviation which first flew in September, 1959, and lastly in October, 1968. Richard Erwin                                           It was powered by ammonia and liquid oxygen and reached altitides above 50 miles while setting speed records for manned flight. As of November 8/10/2009                                                 2008, it still holds the world record for the fastest speed ever achieved by a manned aircraft. Dropped from a B-52, the X-15 reached a maximum                                                                    altitude of 67 miles and a maximum speed of mach 6.72, or 4,520 mph. On the 191st flight, the pilot, Michael J. Adams was killed when his plane                                                                    broke apart during its descent.