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Space Station

X-15: The plane that helped create the Space Shuttle

About the author

Richard is a science journalist and presenter of the Space Boffins podcast. He edits Space:UK magazine for the UK Space Agency, commentates on launches for the European Space Agency and is a science presenter for BBC radio. You can also follow him on Twitter or Facebook.

  • Space Needle
    The X-15 flew 199 test flights in the 1950s and 60s, taking pilots to the very edge of space. (Nasa)
  • Shuttle pioneer
    Flying at heights of up to 100km, the three X-15s enabled high-altitude research, paving the way for the Space Shuttle. (Nasa)
  • Launched from the air
    The X-15 didn’t take off under its own power; instead, it was carried aloft by a modified B-52 bomber and then launched in flight (USAF)
  • Faster than a bullet
    No manned aircraft has yet beaten the X-15’s speed records; at full throttle, the plane could travel at speeds up to 4,500mph (7,270km/h). (Science Photo Library)
  • Into space
    Two flights in the X-15 were so high – more than 100km above the Earth’s surface – that they technically qualified as space flights. (Nasa)
  • Famous flier
    The first man to walk on the Moon, the late Neil Armstrong, was an X-15 pilot before joining the space programme. (Nasa)
  • Seal of approval
    The X-15’s role in helping pave the way for the Space Shuttle was marked with a special commemorative stamp in 2006. (Nasa)
  • New lease of life
    The X-15’s influence is still felt; reuseable spaceplanes that can land under their own power now have private backing, such as Virgin’s SpaceShipTwo. (Virgin Galactic)
  • Orbital rival
    Another spaceplane using techniques pioneered by the X-15 is the Dreamchaser, developed by Sierra Nevada Space Systems. (Sierra Nevada)
The X-15 is the fastest and highest-flying manned aircraft. Decades after its record-breaking flights, it’s inspiring a new generation of space planes.

To any fan of aviation or space history Edwards Air Force Base in California is hallowed ground.

A Harrier jump jet taxis to the runway. Behind it is the vast expanse of flat dry lake floor that made this remote desert location so suitable for landing after dangerous test flights. A few metres away, the fenced-off area where the Bell X-1 was refuelled before the world’s first supersonic flights in the late 1940s. Nearby, a preserved cluster of the weird looking machines that enabled pilots to push the boundaries of the possible. Among them, the stubby wings of the tiny experimental aircraft made famous by the 70s TV series The Six Million Dollar Man.

(Nasa)

The X-15 was launched in flight from under the wing of a modified bomber; future spaceplanes may also be air-launched (Nasa)

I am here to see a life-sized model of one of the most important aeroplanes ever flown: the North American X-15. These days it is tucked away, out of public view, behind the back of a hangar. But 50 years ago the experimental rocket plane this model represents flew higher and faster than any piloted aircraft before or since. In fact this joint military and Nasa project is better described as the world’s first hypersonic spaceplane. The X-15 resembles not so much a plane as an oversized dart – a needle-nosed torpedo with stubby wings, built around a rocket engine that could propel it to speeds in excess of 4,500mph (7,270km/h). That’s London to New York in 45 minutes.

“In terms of manned aircraft, this was the pinnacle, it made records that have yet to be broken,” says Stephanie Smith, a US Air Force historian at the base, standing beside the battered black fuselage of the dart-shaped plane. “This was the most productive research programme for aviation ever and really gave it that leap forward.”

Over a period of nearly 10 years beginning in 1959, the titanium-clad X-15 flew 199 missions, reaching more than four-and-a-half times the speed of sound. On several occasions, its single giant rocket motor propelled it beyond the atmosphere out into space and the pilots saw the horizon turn from blue to black as they hurtled beyond our planet’s sky. After less than 10 minutes of flight, they would return to Earth to skid to a halt on the Edwards lake floor. Remarkably, only one test pilot was killed in all those flights.

As well as proving that an aircraft could fly from air to space and back again, other achievements from the X-15 programme include the development of the first space suits, the study of thermal protection systems for re-entering the atmosphere and the application of advanced avionics. Some of the flights were equipped with instruments to observe and study the hostile space environment.

“People at Edwards really looked up to those aviators, those astronauts, who flew the X-15,” Smith says. “They idolised them – even the people who worked with them on the project really looked up to those pilots as being out there on the cutting edge, taking the risks.”

(Sierra Nevada)

New designs, such as the Dreamchaser, are following in the X-15's footsteps (Sierra Nevada)

Unlike Nasa’s heavily promoted silver-clad astronauts who flew in the Mercury, Gemini or Apollo capsules, only one X-15 pilot became well known. But not for flying the X-15. “Neil Armstrong is remembered here as a co-worker and X-15 pilot,” says Smith, “and not for what he later went on to become, an astronaut with worldwide fame.”

Until recently, the X-15 was a footnote in aviation history, remembered – if at all – as a stepping stone to the Space Shuttle, itself now a museum piece. But, 50 years on, its significance is being rediscovered. In this new space era of the 21st Century, space planes and hypersonic aircraft are back on the agenda and the X-15 is finally getting the recognition it deserves.

This month Nasa’s Dryden Flight Research Center – located on the Edwards base  – was renamed the Armstrong Flight Research Center, in honour of the astronaut’s work on the X-15. Meanwhile, half-an-hour’s drive away at the Mojave Air and Space Port, several private companies are revisiting X-15 concepts.

Virgin Galactic’s spaceplane, which is being built at Mojave, will fly a similar profile to the X-15. Just like the X-15, the company’s SpaceShipTwo will be dropped from beneath a carrier aircraft, to climb under its own power, supersonically, out into space before gliding back to a runway landing. The first flights into space are due to take place later this year.

“We all owe a great deal to the pioneers of spaceflight and aviation,” admits Virgin Galactic’s CEO, George Whitesides, “because they showed it was actually possible.”

Although the materials, electronics and structure of Virgin’s spaceplane are vastly different to the X-15, the basic principles of flying into space and back safely are the same.

“In 2014, we know that you can put a vehicle through Mach 3 but when these folks were doing it for the first time, 50 years ago, we didn’t know that,” he says. “It’s easy to forget what an unknown world it was back then.”

(Virgin Galactic)

Virgin Galactic's SpaceShipTwo spaceplane is expected to start commercial flights in 2015 (Virgin Galactic)

Virgin’s rival, XCOR, also credits the X-15 as inspiration for its Lynx spaceplane. “The key elements of it date back to the Nasa research aircraft of the 1950s and 60s,” the head of XCOR, Jeff Greason, tells me. “What’s new is developing a smaller vehicle that’s commercially viable that has those same capabilities.”

It is not only space tourism companies that are revisiting the concepts of the X-15. Nasa has put more than $100m into the Dream Chaser. Like the Space Shuttle, this spaceplane would be launched into orbit vertically on a rocket and then return to Earth for a runway landing.

However, it is not only the flying capabilities and technical achievements of the X-15 that are being rediscovered. There is also something futuristic – romantic even – about the concept of a reusable space plane rather than a space capsule.

Smith says this point was illustrated by a cartoon drawn by a Nasa engineer in 1966: “It shows the difference between being rescued from your capsule by the navy, as you’re floating in the ocean surrounded by sharks, versus the cool pilot that gets to just walk out onto the runway and step into a convertible with a pretty girl at the wheel.”

In the coming years, clients of Virgin Galactic and XCOR should be able to realise that dream. The X-15 showed a vision of the future – an aircraft that was also a spacecraft – which is now being rediscovered. Future space travellers may just owe the pioneers behind the X-15 an enormous debt.

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