X-15 aircraft was designed mainly for study of hypersonic speeds, that is, over Mach 5. The other application of this program was the exploration of the possibilities of flight above the atmosphere or what is called the “outer space”, that is, flight above 100,000 meters.The “drop” of the X-15 was made at 800 km/h and more than 13,000 meters altitude, then, the aircraft accelerated up to 6,000 km/h at heights of more than 80,000 meters, quite an achievement.The X-15 had parts of the fuselage built with nickel alloys, more specifically “Inconel X-750”, to be able to withstand the high temperatures generated at those speeds and altitudes.The first flights were made with two Reaction Motors XLR11 liquid-propellant rocket engines with only 71 kN of thrust. Finally at the end of 1960 the XLR99 engine of 250 Kn was ready and allowed the X-15 to reach its records and its glorious fame.In November 1962, the No.2 X-15 had a serious accident when making an emergency landing on Mud Lake near the Edwards AFB. Then, It was decided to rebuild the aircraft with some modifications such as a lengthened fuselage and the assembly of two drop tanks for additional fuel. This version was designated as X-15A2.The propellant of the XLR11 engine was composed by ethanol and liquid oxygen, nonetheless, the XLR99 engine used liquid oxygen and anhydrous ammonia. The propellant developed a “specific impulse” of 140 seconds, that is, it provided thrust to the engines during this time.The X-15‘s pilots had controls to handle the rocket motor, (RCS or “reaction control system”), and controls for the “flight control surfaces” that allowed it to maneuver the aircraft. When the fuel ran out, the engine ran out of thrust and the X-15 could not maintain the altitude, then, it glided until landing.When the X-15 reached 100,000 meters in height, this is in outer space, it could only be controlled with small reaction engines, just like spacecrafts. Astronaut Neil Armstrong was one of the 12 pilots who participated in the X-15 program before his arrival on the Moon.
