American X-15 and its systems. Once it was ready to fly, it was his job to demonstrate its airworthiness at speeds ranging up to Mach 3 (2,290 mph). Because the X-15 and its systems were unproven, these tests were considered extremely hazardous. Crossfield flew 14 of the 199 total X-15 flight tests with most of these tests establishing and validating initial key parameters. Crossfield was not only involved with the design of X-15 from the beginning, but introduced many innovations, including putting engine controls of the rocket plane into the cockpit. Previously, all engine adjustments resulted from technicians making adjustments on the ground based upon results of flight profiles. It was during this time that Crossfield was part of the U.S. Air Force's Man In Space Soonest project. On June 8, 1959, he completed the airplane's first flight, an unpowered glide from 37,550 feet. The flight was troubled as the flight controls had not been set up properly. As Crossfield attempted to land the unfueled X-15, it went into what Crossfield described as "a classic PIO" or pilot induced oscillation. He managed to set down the X-15 on the desert runway at the bottom of one of the severe oscillations saving himself and the airframe. On September 17, 1959, he completed the first powered flight. Because of delays in the development of the X-15's mammoth 57,000 pounds force (254 kN) thrust XLR-99 engine, the early flights were completed with a pair of interim XLR-11 rocket engines. Shortly after launch on his third flight, one of these engines exploded. Unable to jettison his propellants, Crossfield was forced to make an emergency landing during which the excessive load on the aircraft broke its back just behind the cockpit. He was uninjured and the airplane was repaired. On June 8, 1960, he had another close call during ground tests with the XLR-99 engine. He was seated in the cockpit of the No. 3 X-15 when a malfunctioning valve caused a catastrophic explosion. Once again he was uninjured as Dr. Toby Freedman, NAA Medical Director, pried open the cockpit to save him and despite being subjected to a later calculated acceleration force of near 50 Gs (although Crossfield stated in the Discovery Channel's series Frontiers of Flight that he began to have debilitating issues with his night vision after the accident) and the airplane was completely rebuilt. On November 15 of the same year,