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The Hypercool X-15 Was Part Jet, Part Spaceplane And All Radical

Men were flying to the fringes of space years before NASA, or the Soviet Union put a guy in orbit around the Earth.

Men were flying to the fringes of space years before NASA, or the Soviet Union put a guy in orbit around the Earth. They weren't astronauts and they weren't launching in a capsule on top of a missile. They were test pilots flying the rocket-powered X-15. It was one of the most interesting test programs and it something different to everyone involved. To some it was the last research aircraft before men entered space. To others, it was the first true space plane. To its pilots, it was a unique aircraft that combined three modes of control into one: It was a jet, a spaceplane, and a glider.

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They don't make 'em like they used to.

The X-15 was conceived in 1954 as the joint brainchild of the National Advisory Committee for Aeronautics (NACA, the precursor to NASA) and the U.S. Air Force. Officially, it was a test program to help engineers learn how an aircraft behaves at high altitudes and high speeds during atmospheric reentry. It was also a means to test whether men could survive a journey into space in an aircraft and make it back safely to a runway landing. This wasn't an incredibly far-fetched either. At the time, aircraft looked like they were going to keep flying higher and faster until eventually they were able to orbit the Earth. But there was no point going into space if the men weren't going to come back.

Almost more of a pilotable rocket tube than an aircraft, the X-15 was tiny. Just 50 feet long with a 23-foot wingspan, it held one pilot in a cramped cockpit. The rest of its body was filled with fuel tanks to fire its massive engine. All told, the aircraft weighed just 34,000 pounds fully fueled — not too heavy for a space plane.

To simulate orbital reentry, the X-15 flew high enough that it actually reentered the atmosphere from near-orbital heights. This was as close to the real thing as it could get. To reach these heights and achieve speeds equivalent to those associated with orbital flight, the X-15 flew a unique flight path.

The X-15 began its flight from a dry lakebed around Edwards, California strapped underneath the wing of a converted B-52 bomber. The X-15's pilot, meanwhile, waited. When the B-52 reached about 30,000 feet, roughly the altitude of a cross-country commercial flight, it released the X-15. Its pilot ignited his main engine and shot up and away from the B-52. Reaching speeds close to Mach 7 (seven times the speed of sound), it flew like a traditional jet aircraft until it exhausted its fuel store.

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Momentum carried the X-15 further until its acceleration was matched by gravity. It was weightless, floating on top of its arcing flight path for a few minutes. But the pilot couldn't enjoy the view, which featured the curvature of the Earth from a peak altitude close to 270,000 feet. His window was pretty tiny but, more importantly, he had to make sure his aircraft was in the right alignment for reentry.

Without any air, traditional controls were useless. And so a second set of controls were inside the X-15's nose and wings — ballistic controls. These fired hydrogen peroxide through tiny thrust rockets to adjust the aircraft's orientation. For these few weightless moments, the X-15 was a true space plane.

As gravity took over and the aircraft began to fall from its peak altitude, the pilot had the difficult task of landing the tiny airplane without any fuel — he'd spent it all during his ascent. This was a challenge. With no fuel he had no chance to try landing a second time if he missed the runway on a first attempt. To make it harder, the X-15 wasn't exactly a good glider. It generated some lift, but it was really designed with atmospheric entry in mind, not gliding. Gliders usually have a wingspan much broader than the fuselage is long. The X-15 had the opposite arrangement. To slow his descent to a relatively manageable landing speed of 200 miles per hour, the pilot traced circles over the runway. He landed on skids. They didn't provide much directional control, but they did slow the speeding aircraft faster than any wheels and traditional brakes could.

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This flight path wasn't an easy one, even for the skilled X-15 pilots. On its first flight, pilot Scott Crossfield smashed the aircraft's nose gear. Subsequent repairs set the program back a few months. Crossfield later landed so hard in the aircraft that it broke halfway between nose gear and rear landing skids. More repairs meant more delays.

Crossfield, however, was lucky. His crash landings were at least on the runway. Neil Armstrong, before he became an astronaut, flew one of the most dangerous flights in the X-15 program. He took the aircraft up to his peak altitude in the upper atmosphere as planned, but couldn't get the X-15's nose down enough to start its fall to Earth. He was stuck, skipping along the atmosphere and moving further and further from the safety of the runway on the dry lakebed.

Eventually, the friction between the X-15's underside and the atmosphere caused the aircraft to begin its descent, but Armstrong was 50 miles south of his landing point. He could try and make it back, or try and land at a small commercial airport that was closer. He chose the lakebed — without power, trying to get in a queue for landing would be impossible and his landing skids wouldn't grip the asphalt like they did dry mud. When he got back to the runway at Edwards, he was flying level with nearby trees. It was a near miss but he made it. The whole ordeal from launch to landing only lasted 12 minutes.

The X-15 was retired in 1970 after making almost 200 flights and setting records that remained unbroken into the 21st century. The highest flight of the program was made by US Air Force Pilot Joe Engle. At 353,760 feet or 67 miles, he was the only pilot whose flight qualified as a space flight by the FAI (International Aeronautical Association). The flight, however, was in 1963 so couldn't qualify as a first since NASA was already steeped in the space race. US Air Force pilot Pete Knight set the speed record flying the X-15 at 4,519 miles per hour in 1967.

Never before or since has a single vehicle been so many things — space plane, jet, glider — and set so many records. The research gathered during the program went beyond its immediate use, too. The data from X-15 flights was used in working out the details of the space shuttle, which was tested in the exact same way as its tiny predecessor.

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