Monday morning, Professor Neil Armstrong (yes, that Neil Armstrong) gave a talk out here in California about his experiences in the X-15 suborbital flight program. The X-15 was America's first dedicated high speed, high altitude, rocket-powered suborbital space plane, and back in the early 1960s it was busy paving the way for the commercial spaceflight development that's one of the most exciting things happening in space today.
Neil Armstrong, who turned 81 last August, doesn't make public appearances very often. When he does, it's usually safe to assume that he's got a good reason for stopping by.
Monday, he was a speaker at the Next-Generation Suborbital Researchers Conference, an event sponsored by the Southwest Research Institute, NASA, and the Commercial Spaceflight Federation to help promote commercial suborbital spaceflight by companies such as XCOR Aerospace and Virgin Galactic, among others.
Professor Armstrong kicked things off on Monday with a talk about the X-15, an air-launched, rocket-powered suborbital spacecraft that he helped pioneer.
In the mid to late 1940s, we knew that it was possible to fly faster than the speed of sound. What we didn't know was whether it was safe.
Weird things started to happen to airplanes traveling at transonic speeds (between about Mach 0.8 and Mach 1.2), and so NASA (it was NACA back then) started to fund X-planes to figure out what was going on. The first aircraft to break the sound barrier in level flight was the Bell X-1, a rocket plane piloted by Chuck Yeager. After that came the X-1A and X-1B, the latter incorporating experimental hydrogen peroxide control thrusters. Armstrong flew four missions in the X-1B, but fuel tank cracking meant that the project had to be shut down. Its successor, the X-2, had its first flight in 1955 and reached speeds approaching Mach 3, but high heat and decreased stability caused severe issues with the aircraft, which was lost on a test flight in 1956.
After that, NACA skipped a few X-plane numbers doing weird stuff, and then built the X-15, pictured above with Armstrong. The X-15 was built specifically to try and tackle two problems: high heat caused by atmospheric friction, and control issues caused by aerodynamic drag. As Armstrong said yesterday:
"The X-15 was designed to fly fast and hot. It was not designed to fly high. But, it was obvious to all that an aircraft that could reach these kinds of speeds would have enough energy to zoom above 100 miles of altitude."
The X-15 was really not much of an airplane. It was a rocket with a cockpit on the front, plus a couple stubby little wings that were just barely large enough to allow for a less-than-suicidal landing speed. The plane couldn't take off on its own, and had to be hauled eight miles up under the wing of a B-52 bomber and then released at 500 mph before starting its rocket engine. The X-15's engine sucked down 15,000 pounds of liquid fuel in 80 seconds to boost the plane up to 67 miles high at a top speed of Mach 6.7, or 4,500 mph. On a ballistic trajectory, the X-15 would travel to space and back, descending "like a brick" (as Armstrong put it) at some 20,000 feet per minute and landing in the desert on skids.
When an airplane gets above about 80,000 feet (15 or 16 miles), as the X-15 was easily capable of, there's not enough air to allow for control through traditional methods like ailerons. Furthermore, the turbopump that supplied fuel to the X-15's rocket engine would continue to spin even after the engine was off, generating gyroscopic yaw forces. To counteract this, the X-15 employed a reaction control system (similar similar in principle to what was used on later orbital spacecraft) that fired puffs of cold gas to give the pilot astronaut control in a vacuum.
So, to sum it up, the X-15 was a rocket plane launched by a carrier aircraft that could fly to suborbital space, orient itself with a gas thruster system, and then glide back to a controlled landing. Sound familiar? Sure it does:
At its heart, Virgin Galactic's commercial spaceflight program (and other rocket planes like XCOR's Lynx) are simply modern implementations of the X-15, constructed with an extra fifty years or so of experience and technological progress. But much of that experience came directly from the X-15 program: until the second spaceflight of Space Ship One in 2004, the X-15 still held the record for highest altitude in a rocket-powered aircraft.
"We were always in Tomorrow Land, always looking at higher speeds and higher altitudes. Our thinking was, we'll make a road map, we'll get the data that's necessary for people to go into suborbital space and do things." - Neil Armstrong
Here at DVICE, we're all about Tomorrow Land. But, today's tomorrows are built on lots and lots of yesterdays, and it took people like Neil Armstrong to push the limits of what was known and what was possible to provide a foundation upon which we can head for the stars.
On location photography by Evan Ackerman for DVICE.