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19th of July 1963

347.800 feet (106.010 meters) was the record altitude reached by NASA test pilot Joe Walker on this day in aviation history. A record he would break himself on the 22nd of August 1963 when he reached an altitude of 107.8oo meters (353674 feet).

Both well above the Kármán line as defined by the Fédération Aéronautique Internationale which they determined to be at an altitude of 100 km.

While the U.S. military, the Federal Aviation Administration, and NASA set the boundary of space at 50 miles (80 km) above ground.

He reached that altitude in a North American X-15.

The Experimental North American X-15 was a rocket-powered aircraft operated by the US Air Force and NASA as part of the X-Plane program of the 1960s.

The X-15 set several records during its operation for speed and altitude, one of them even still standing today! In October 1967 one of the X-15 pilots flew an X-15 at Mach 6.7 (4,520 mph 7,274 km/h) at an altitude of 102100 feet (31.120 meters), this is still the highest speed ever flown by a manned powered aircraft, an official world record! Only 12 pilots flew the X-15, of which only 3 were built, in total 199 missions were flown with the X-15.

The X-15 was built by two companies, North American for the airframe and Reaction Motors for the (rocket) powerplant. Two USAF B52 bombers were modified to bring the X-15 to launch altitude, which was about 45.000 ft (13.700 meters).


X-15 being carried by its NB-52B mothership (52-0008), with T-38A chase plane


The long cylindrical fuselage of the X-15 had short stubby wings and dorsal and ventral fins that acted as stabilisers. It had a retractable landing gear with a single nose wheel and skids on the main landing gears. The main landing gears were shorter than the ventral fin, just before landing the pilots would jettison the ventral fins which would descent by parachute, be recovered and re-used!


As the aircraft was operated at an altitude where aerodynamic control was insufficient, it was equipped with a Reaction Control System that used rocket thrusters with a 140 second operational supply of propellant. The first 24 flights of the X-15 were powered by two liquid-propellant rocket engines, each providing 16.000 lbs (71 kN) of thrust, the Reaction Motors XLR11 liquid-propellant rocket engine.

In late 1960 Reaction Motors delivered a new rocket engine for the X-15, the XLR99 rocket engine, providing 57.000 lbs (250kN) of thrust and future flights of the X-15 were all powered by a single XLR99 rocket engine which burned through the aircraft supply of 15.000 lbs of propellant in 80 seconds.


A total of 5 aircraft were actively involved in the X-15 project, 3 X-15 aircraft and 2 modified B52's:

  • X-15-156-6670, 81 free flights

  • X-15-2 (later X-15A-2) – 56-6671, 31 free flights as X-15-2, 22 free flights as X-15A-2; 53 in total

  • X-15-356-6672, 65 free flights, including the Flight 191 disaster, killing the pilot

  • NB-52A52-003 nicknamed The High and Mighty One (retired in October 1969)

  • NB-52B52-008 nicknamed The Challenger, later Balls 8 (retired in November 2004)

Some specifications for the X-15:

  • Crew: One

  • Length: 50 ft 9 in (15.47 m)

  • Wingspan: 22 ft 4 in (6.81 m)

  • Height: 13 ft 3 in (4.04 m)

  • Wing area: 200 sq ft (19 m2)

  • Empty weight: 14,600 lb (6,622 kg)

  • Gross weight: 34,000 lb (15,422 kg)

  • Powerplant: 1 × Reaction Motors XLR99-RM-2 liquid-fuelled rocket engine, 70,400 lbf (313 kN) thrust (from flight 25 and on)

  • Maximum speed: 4,520 mph (7,270 km/h, 3,930 kn)

  • Range: 280 mi (450 km, 240 nmi)

  • Service ceiling: 354,330 ft (108,000 m)

  • Rate of climb: 60,000 ft/min (300 m/s)

  • Thrust/weight: 2.07

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