A spaceplane is quite simply a vehicle that can fly as both an airplane in the atmosphere—generating lift from its wings—and as a spacecraft in a vacuum using rocket propulsion. No spaceplane has yet been built that can both take off and land as an ordinary plane and also travel into space. However, there have been five successfully flown vehicles to date that fall into the spaceplane category and many others still on the drawing board.
The earliest technical study of the feasibility of spaceplanes was carried out by the German scientist Eugene Sänger in the 1930s and published in his book “The Technology of Rocket Flight.” Sänger went on to assemble a variety of ramjet engines, one of which he tested on a Dornier 217 in April 1942. After the war, Sänger’s work on hypersonic flight served as the basis for the development of the X-15 and, ultimately, the space shuttle.
Built by North American and operated by the U.S. Air Force and NASA, the X-15 set records for speed and altitude by an aircraft—some of which still stand today. It was both a rocketplane and a suborbital spaceplane, its Reaction Motors rocket engine powering it to speeds in excess of 4,000 mph and a peak altitude of 67 miles. On a regular basis it flew higher than the Air Force’s definition of the edge of space (50 miles, or 80 km) and twice went beyond the atmosphere as defined by the International Federation of Aeronautics (FAI)—the so-called Karman line at 62 miles (100 km).
The space shuttle was the first orbital spaceplane, but unlike the X-15, which was carried up under a B-52 mother ship, was launched vertically with the help of a rocket stack combining both expendable and reusable components. Once in orbit it had no means of propulsion other than maneuvering thrusters and could only glide back to a runway on Earth. The Soviet Union’s Buran, closely modeled on the shuttle but capable of automatic flight, made just one trip into space, in 1988, before the program was scrapped through lack of funding.
Like Buran, the Boeing X-37, which started out as a NASA project in 1999 but is now operated by the U.S. Air Force, is launched by an expendable rocket, flies without a pilot, and lands automatically on a runway. It’s the only one of various spaceplace concepts in the long-running X-plane series to have actually reached orbit and returned successfully.
The future of spaceplanes may lie largely in the private sector. But Rutan’s Scaled Composites company has already successfully flown its SpaceShipOne beyond the Karman line at speeds exceeding Mach 3 and is now testing the much larger SpaceShipTwo capable of lofting a two-man crew and up to six fee-paying passengers on suborbital flights. Virgin Galactic plans to start commercial flights using this innovative craft within a couple of years.
A long-standing dream of rocket scientists and engineers is to build a single-stage-to-orbit spaceplane that would both take off and land under its own power using a conventional runaway. Overall weight is a major problem with this kind of approach, since the vehicle must carry all the fuel it needs for the round trip, as well as its own weight plus payload, into orbit. The nearest thing to such a vehicle currently under development, by Reaction Engines in the UK, is Skylon—an un-piloted spaceplane with a 15-ton payload capacity, powered by twin engines that can run combined air-breathing and rocket cycles. Ultimately, the development of spaceplanes, both for access to orbit and hypersonic suborbital flights between major cities, is likely to be driven by commercial demand.
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