(^74) UNITED STATES
H
alf aircraft, half spaceship, the
North American X-15 rocket-
powered research vehicle bridged
the gap between manned flight within the
atmosphere and manned flight into space.
After completing its initial test flights in
1959, the X-15 became the first winged
aircraft to attain velocities of Mach 4, 5, and
6, albeit for only a few minutes.
Development of the X-15 began in 1954, in
a joint research programme sponsored by the
National Advisory Committee for Aeronautics
(NACA, the forerunner of NASA), the US Air
Force, the US Navy, and private industry. North
American was selected as prime contractor
on the project and three rocket-powered
X-15s were built. Because of its high-speed
capability, the outer skin consisted of a nickel-
chrome alloy called Inconel X, employed in
a heat sink structure to withstand the results
of aerodynamic heating when the aircraft
was flying within the atmosphere. The first
X-15 arrived at the NASA High-Speed Flight
Station in the early months of 1959, and Scott
Crossfield, who had helped with the design
of the aircraft, soon began the contractor
demonstration flights.
The aircraft was powered by a Thiokol
(Reaction Motors Division) XLR-99 throttleablerocket engine powered by anhydrous ammonia
and liquid oxygen. It provided a maximum
thrust of 57,000lb and a minimum thrust of
28,000lb. Because of the large fuel consumption
of its rocket engine, the X-15 was air launched
from a B-52 at about 45,000ft and speeds
upward of 500mph. Depending on the mission,
the rocket engine provided thrust for the first
80 to 120 seconds of flight. The remainder
of the normal 8- to 12min flight was without
power and ended in a 200mph glide landing.
Because the nose landing wheel lacked steering
and the main landing gear employed skids, theNorth American X-15
X-15 had to land on a dry lakebed. The Rogers
Dry Lake adjacent to Edwards and Dryden was
the intended landing location for all flights,
but there were numerous emergency lakebeds
selected in advance if needed.
The X-15 required conventional aerodynamic
control surfaces to operate within the
atmosphere and special ‘thruster’ reaction
control rockets located in the nose and wings
of the aircraft to enable the pilot to maintain
control when flying on the fringes of space.
During the 10 year programme, 13 flights by
eight pilots met the US Air Force spaceflightRight: Test pilot Neil Armstrong prepares for a
flight in the X-15 in 1961. Even in his wildest
dreams he could not have imagined that just
eight years later he would be travelling even
faster on his way to walking on the moon.