The X15 Project

The X-15 brought the old chauffeurs versus airmen dichotomy into the world of spaceflight and computerized control. It introduced changes in engineering practice and the role of the pilot that had significant personal, institutional, and technological connections with the Apollo program.

The black airplane had a radical appearance, but it was a logical, incremental step from the Bell X-1, consisting of a straight beam of a fuselage, short, stubby wings, a pilot up front and a rocket engine in the back. No fragile, crunchable airframe this: the entire aircraft was made out of a high-temperature alloy with the space-age moniker ''Iconel-X.'' Far from the sheet aluminum normally found on the skin of an aircraft, Iconel-X was heavy-duty stuff for building pressure vessels and turbine blades, not light, delicate airplanes. The important feature of Iconel-X was its high melting point, so it could withstand the extreme temperatures of hypersonic flight.

NACA administrator Dryden described the flight path of the X-15 as being ''like a fish leaping out of the water'' because of its unusual parabolic arc into space. A B-52 bomber, converted for research purposes, would fly the aircraft to a launch altitude slung under its wing like a parasite on the belly of a shark. At about forty-five thousand feet, the bomber would drop the vehicle;a few seconds later (and a few hundred feet below) the pilot would start the engine, rapidly leaving the host behind. After accelerating to supersonic speeds, the pilot would pitch up and fly nearly straight up, passing out of the atmosphere into space. After just a minute or two, the rocket would cut off, and the vehicle would zoom up on a parabolic trajectory (figures 3.1 and 3.2).

As the pilot rocketed out of the atmosphere, he could maneuver the vehicle's attitude (i.e., its orientation) using small thrusters or ''reaction controls.'' As it rounded the top of its arc, the pilot would point the X-15 back toward earth. Slowly at first, the craft would descend, and as it approached the atmosphere the pilot would pitch the nose up, to a high ''angle of attack'' (the angle between the airflow and the wings) for

Figure 3.1

X-15 being dropped from a B-52 bomber. (NASA Dryden photo E-4942.)

Figure 3.1

X-15 being dropped from a B-52 bomber. (NASA Dryden photo E-4942.)

X-15 RESEARCH MISSIONS

Figure 3.2

X-15 mission profiles, showing launch from a B-52 bomber and parabolic rise into space before reentry and landing at Edwards Air Force Base. Two trajectories are shown, one optimized for speed and the other for altitude. (NASA Dryden photo E-616586.)

Figure 3.2

X-15 mission profiles, showing launch from a B-52 bomber and parabolic rise into space before reentry and landing at Edwards Air Force Base. Two trajectories are shown, one optimized for speed and the other for altitude. (NASA Dryden photo E-616586.)

reentry. After a series of turns and maneuvers to bleed off speed, the pilot brought the machine in for a ''dead stick'' (with no power) landing at Edwards (or another of the many lake beds around California and Nevada if something had gone wrong). The whole flight, from the drop of the B-52 to the landing, lasted barely ten minutes. Still, it was expensive, requiring an array of chase planes, rescue craft, and support helicopters.

The whole sequence was tracked and observed from a network of antennas and tracking stations dotted throughout the West. Known as the ''high range,'' the network continuously logged the aircraft's position and speed and downloaded measurements from the vehicle itself. A master control station at Edwards coordinated all the data and plotted it on paper for engineers to monitor in real-time.8 During the flight, the pilot was constantly in touch with engineers and flight controllers on the ground. A few years later, when NASA built a global network of stations to track the Mercury spacecraft as it orbited the earth, it explicitly modeled it on the X-15's high range, as well as on the X-15's ground-control protocols.

Yeager's original supersonic flights had been shrouded in secrecy;the X-planes of the 1950s, and initially the X-15, were not secret, but were the comparatively esoteric stuff of high-speed flight research. That changed in 1957, when the government and the public panicked in response to Russia's successful Sputnik launch. Suddenly, the X-15 assumed a new prominence as the sole U.S. endeavor to send men into space. For a brief period it became the darling of the press, hailed as a savior, the only American project that even had a hope of putting people in space.

In October 1958 NASA came into being and North American first rolled out the X-15, with Vice President Richard Nixon in attendance at Edwards. In September 1959 it flew under its own power for the first time, achieving Mach 6 and higher than 200,000 feet by the end of 1961. The X-15 flew until 1969, so the program experienced several different phases, the later ones obscured by the glare of Apollo. But when it first flew in 1959 it was the leading manned aerospace project in the country, pushing the envelope for human control.

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