19 July 1963: Between 1960 and 1963, NASA Chief Research Test Pilot Joseph Albert Walker made 25 flights in the North American Aviation X-15A hypersonic research rocketplanes. His 24th flight was the 21st for the Number 3 X-15, 56-6672, and the 90th of the X-15 program.
At 10:20:05.0 a.m., Walker and the X-15 were airdropped from the Boeing NB-52B Stratofortress, 53-008, Balls 8, over Smith Ranch Dry Lake, Nevada. Walker fired the Reaction Motors XLR99-RM-1 rocket engine and over the next 84.6 seconds the engine’s 60,000 pounds of thrust drove the X-15 upward. The engine’s thrust on this flight was higher than expected, shutdown was 1.6 seconds late, and Walker’s climb angle was 1½° too high, so the X-15 overshot the predicted maximum altitude and its ballistic arc peaked at 347,800 feet (106,010 meters, 65.8 miles). The maximum speed was Mach 5.50 (3,714 miles per hour, 5,977 kilometers per hour).
Walker glided to a touch down at Rogers Dry Lake, Edwards Air Force Base California, after flying 311 miles in 11 minutes, 24.1 seconds of flight. On this flight, Joe Walker became the first American civilian to fly into Space.
18 November 1966: On Flight 175 of the research program, Major William J. (“Pete”) Knight, U.S. Air Force, flew the newly-modified North American Aviation X-15A-2, 56-6671, to Mach 6.33 (4,261 miles per hour/6,857 kilometers per hour) at 98,900 feet (30,245 meters). This is just 11 years, to the day, since Pete Everest made the first powered flight in the Bell Aircraft Corporation X-2 rocketplane, with more than 6 times an increase in speed.
On this date, NASA made an attempt to launch two X-15s, -671 and -672, using the NB-52A 52-003 and NB-52B 52-008. However -672, the number three ship, had to abort the mission.
Balls 8, the NB-52B, flown by NASA test pilot Fitz Fulton and Colonel Joe Cotton, USAF, carried 56-6671 to the launch point over Mud Lake, Nevada, approximately 200 miles to the north of Edwards AFB. (This was the lake where -671 was severely damaged in an emergency landing, 9 November 1962. It was returned to North American to be rebuilt to the X-15A-2 configuration and returned to flight operation 19 months later.)
At 1:24:07.2 p.m. local time, Pete Knight and the X-15 were dropped from the pylon under the right wing of the B-52. He ignited the Reaction Motors XLR99-RM-1 and began to accelerate with its 57,000 pounds of thrust (253.549 kilonewtons).
Since this was to be a high temperature test flight, it was planned to fly no higher than 100,000 feet (30,480 meters). The denser atmosphere would result in greater aerodynamic heating of the rocketplane.
With the two external propellant tanks carrying an additional 1,800 gallons (6,814 liters) of liquid ammonia and liquid oxygen, the engine ran for 2 minutes, 16.4 seconds. The rocketplane had accelerated to Mach 2. The external tanks emptied in about 60 seconds and were jettisoned. The tanks were equipped with parachutes. They were recovered to be reused on later flights.
The X-15, now about 25,000 pounds (11,340 kilograms) lighter and without the aerodynamic drag of the tanks, continued to accelerate. At its highest speed, the rocketplane was travelling approximately 6,500 feet per second (1,981 meters per second), more than twice as fast as a high-powered rifle bullet. Its surface temperatures exceeded 1,200 °F. (649 °C.)
Knight landed the X-15 on Rogers Dry Lake at Edwards Air Force Base. The duration of this flight had been 8 minutes, 26.8 seconds.
21 August 1967: On the 186th flight of the X-15 program, the modified North American Aviation X-15A-2, 56-6671, made the first of two flights with a heat-protective ablative coating, designed to protect the steel structure of the rocketplane from the extreme heat of flight at high Mach numbers.
After a landing accident which caused significant damage to the Number 2 X-15, it was rebuilt by North American. A 28-inch (0.71 meter) “plug” was installed in the fuselage forward of the wings to create space for a liquid hydrogen fuel tank which would be used for an experimental “scramjet” engine that would be mounted the the ventral fin. The modified aircraft was also able to carry two external fuel tanks. It was hoped that additional propellant would allow the X-15A-2 to reach much higher speeds. The external tanks were not carried on the 21 August 1967 flight.
With Major William J. (“Pete”) Knight, U.S. Air Force, in the cockpit, the X-15A-2 was airdropped from the Boeing NB-52B Stratofortress, 52-008, known as Balls 8, over Hidden Hills Dry Lake, just on the California side of the border with Nevada. This was Knight’s 11th X-15 flight, and the 52nd flight for 56-6671. The launch time was 10:59:16.0 a.m., PDT. Knight fired the 57,000-pound-thrust Reaction Motors XLR99-RM-1 rocket engine and accelerated for 82.2 seconds. The purpose of this flight was to attain a high speed rather than altitude. The X-15A-2 reached Mach 4.94 (3,368 miles per hour, 5,420 kilometers per hour) at 85,000 feet (25,908 meters) and reached a peak altitude of 91,000 feet (27,737 meters). Pete Knight touched down on Rogers Dry Lake at Edwards Air Force Base, just 7 minutes, 40.0 seconds after launch.