In the 1950s, it looked like aircraft were going to keep flying higher and faster until one went so high and so fast that it entered space. The spaceplane was an attractive concept, in large part because it took advantage of the pilot's skill. But spaceflight, in a spaceplane or some other vehicle, was largely unknown in the 1950s. Could an aircraft-inspired spaceplane sustain the heat and structural stresses associated with spaceflight? And could the pilot control the vehicle throughout the flight?
The X-15 was designed to answer those questions, and Armstrong flew it to the fringes of space and glided to a landing on the dry lakebed at Edwards Air Force Base. The X-15 was small, just 50 feet long with a wing span a little over 23 feet, and solid. The wings were constructed of Inconel X skins over titanium frames bolted to the fuselage. Driving down the highway towed behind a truck, an X-15 sliced the roof off an unsuspecting driver's camper without sustaining so much as a scratch.
The X-15 was also almost all fuel tank, but it was too small to reach the upper atmosphere. To compensate, it began it's flight at about 30,000 feet (about the average cruise height for a cross country flight). It was released from underneath the wing of a B-52 bomber, the the X-15 pilot would fire its engine and shoot upwards faster than the speed of sound until he ran out of fuel. Momentum would carry it over the top of an arcing flight path where, in the thin upper atmosphere, rockets in the aircraft's nose gave him directional control.
Having used up all his fuel, the X-15 pilot made a completely unpowered descent meaning he had one shot to land. The aircraft became a glider, a very unlikely glider with a wingspan shorter than its body (gliders are typically the opposite). This configuration made the X-15 great during it's powered ascent but it glided about as well as a stone. Falling to Earth, the pilot traced out large circles above the runway to slow his speed to a manageable 230 miles per hour at landing.
Individual X-15 flights varied in terms of speed and maximum altitude, but they all followed this same basic flight plan. And they were short flights, typically less than ten minutes. Armstrong, inadvertently, set the duration record for the program on April 20, 1962.
The purpose of this flight was to evaluate a new control system designed to give the pilot better control of the X-15 throughout its different flight phases. Jumping from subsonic (slower than sound) speeds to hypersonic speeds up to five time the speed of sound can bring on sudden and serious control problems, something this new control system hoped to eliminate.
Armstrong separated from his B-52 launch plane and accelerated past Mach 5 with ease and in control of the aircraft. An unexpected problem developed when he tried to aim the aircraft back towards the runway at Edwards. He was in the thin upper atmosphere, and with the X-15 nose angled upwards, he bounced off the atmosphere instead of pitching his nose down to make the turn. The X-15 skipped off the atmosphere like a stone on water, carrying him further from Edwards. Gravity eventually took over and he was able to set himself back on track for landing. The only problem was that he was 50 miles south of where he wanted to be, and he didn't have an engine to light to get him any closer.
Making his situation worse, there weren't any safe lakebeds for an emergency landing between him and Edwards; all the emergency lakes were too far north to reach. He thought briefly of a small airport in Palmdale, California, but it wasn't an attractive solution. He had no power so couldn't work into the landing schedule at a busy airport. The runway at Palmdale was concrete and the X-15 had metal skids instead of wheels for landing gear. Skids were great for landing on dry mud, they acted as brakes. Landing with skids on a runway would likely be a disaster.
There weren't any good options. He was going to have to try and make it back to Edwards.
And make it he did, reaching the southern edge of the lakebed with just feet to spare. One of the pilots following him in an F-104 chase plane saw Armstrong in the X-15 flying level with the surrounding trees he was so low coming in to land. But he managed a safe landing.
The flight, which lasted 12 and a half minutes, was jokingly referred to as Armstrong's cross country flight.
Image: Neil Armstrong standing alongside an X-15. Credit: NASA