Successors to the Shuttle

Despite the Space Shuttle's checkered history and imminent retirement, the concept of the spaceplane has too many benefits to disappear completely. So what will the next generation of spacecraft look like?

SANGER'S AMERIKA

Eugen Sanger's Second World War design for a rail-launched German orbital bomber, called Amerika, is still an inspiration for many aerospaceplane concepts today.

Sanger in the 1930s, were rocket-powered aircraft launched horizontally on a rail track, accelerated to high speed before takeoff by a rocket-propelled shunt that remained on the ground.

Several possible designs for the Space Shuttle used carrier aircraft that would fly to the edge of space and then release a smaller spacecraft to continue into orbit. They were rejected due to the impractical size of the carrier craft, but the concept, used by the Bell X1 (see p.34) and the X-15 (see p.188), has been revisited and proven again by the privately developed SpaceShipOne (see p.309).

An alternative is the hybrid aerospaceplane - a spacecraft that behaves like a normal aircraft in the atmosphere, accelerating to hypersonic speeds before transforming into a rocket at high altitudes.

HYPER-X

Even before the Shuttle first flew, a range of ideas were circulating about what might ultimately replace it. The Shuttle design is far from economical, since it is only partially reusable: the key to cheap spaceflight lies in simple, fully reusable vehicles that can launch, return to Earth intact, and be ready for another flight after minimal servicing. Countless solutions to this challenge have been proposed, but the history of spaceflight is littered with their remains,

Next-generation spaceplanes

One of the most popular routes has been the Shuttlelike, full-sized spaceplane, sometimes reduced to a single stage or stacked in a reusable design similar to the British MUSTARD (see p.188). The very first spaceplanes, envisioned by Austrian engineer Eugen

The X-43C was a NASA-led attempt of the early 2000s to develop a hypersonic aircraft powered by a scramjet (an advanced ramjet) and capable of reaching 8,000kph (5,000mph), as a prototype for future spaceplane projects.

Mach Aircraft

THE HOTOL SPACEPLANE

SPACE STATION LIFEBOAT

The X-38 was a prototype of a lifting body Crew Return Vehicle intended for use on the ISS. It passed a number of drop tests from a NASA B-52 before its cancellation in 2002.

MILITARY TAKEOVER

The X-37 experimental launch vehicle was first developed by NASA as a potential Shuttle successor, but has since been taken over by the DARPA defence agency. A new version is intended to launch on an Atlas rocket in 2008.

SPACE STATION LIFEBOAT

The X-38 was a prototype of a lifting body Crew Return Vehicle intended for use on the ISS. It passed a number of drop tests from a NASA B-52 before its cancellation in 2002.

MILITARY TAKEOVER

The X-37 experimental launch vehicle was first developed by NASA as a potential Shuttle successor, but has since been taken over by the DARPA defence agency. A new version is intended to launch on an Atlas rocket in 2008.

When the concept was first suggested in the 1980s, in forms such as the British HOTOL and the US National Aerospace Plane (NASP), the technology required to make such vehicles a reality was still in its early stages of development. Now that ramjets have matured (see panel, below), the idea is being revisited in earnest.

TECHNOLOGY

RAMJETS

Many spaceplane concepts rely on ramjet technology to help them fly through the atmosphere. A ramjet is a jet engine with few moving parts - rather than using turbines to draw in air for combustion, it relies on its own forward motion to force air into it at high speed. The shape of the engine then compresses and heats the air until fuel is injected, and the combustion produces thrust. Ramjets are often incorporated into the airframe of an aircraft - as seen in NASA's X-43A (right). Because they rely on their own forward motion, they are only effective at speeds of 1,600kph (1,000mph) or more, so another engine is needed to reach these speeds. Fortunately, the rocket engines needed to operate in space can also be used to gain to speed.

Mini-shuttles

A variety of proposals for small, Shuttle-like spacecraft have come and gone over the years. However, most of these transport craft would use the spaceplane concept only for atmospheric re-entry -they would be launched in a more conventional way, mounted on top of a rocket. This gives them more

combustion chamber

THE HOTOL SPACEPLANE

The HOTOL (Horizontal Take-Off and Landing) spaceplane was a British project of the late 1980s that was among the first to use an air-breathing rocket engine. This would have drastically reduced the amount of liquid oxygen needed to combust with HOTOL's liquid hydrogen fuel. Along with a rocket-assisted launch sled for an initial speed boost, it would have allowed the spacecraft to reach low Earth orbit with a 7,000kg (15,5001b) payload, gliding back to Earth at the end of its mission. The project stalled in 1988, a victim of repeated modifications as the designers tried to compensate for the massive weight of the engine and the payload capability became too small for viability. An attempt to develop a modified version, to be launched from a Russian An-255 transport aircraft, was abandoned in the early 1990s.

fuel injection

igniter flameholder fuel pumps and controls combustion chamber exhaust exhaust fuel pumps and controls igniter flameholder than a passing resemblance to the US Air Force's Dyna-Soar project of the 1960s. Examples of such "mini-shuttles" include ESA's Herm├Ęs project (see p.231), Japan's similar HOPE (H-ll Orbiting Plane), and a proposed Crew Return Vehicle for the International Space Station. Russian space contractor Energia is currently developing a similar spacecraft called Kliper, which might fly as early as 2012.

Single stage to orbit

Another radical approach to the problem of reusable launch vehicles is to integrate spacecraft and rocket so that the entire vehicle travels into space and returns to Earth intact. This single-stage-to-orbit (SSTO) concept was developed and tested by the McDonnell-Douglas Delta Clipper or DC-X, as part of the SDI "Star Wars" project (see p.287). DC-X made short flights several times during the early 1990s (the prototype was not intended to reach space) and was taken on by NASA after the SDI budget was slashed. However, NASA already had a competing project, the X-33, in development, and when DC-X caught fire during a test in 1996, the project was abandoned (X-33 followed it into oblivion a few years later). Despite NASA's loss of interest in the project, the SSTO concept is sound, and the potential savings on putting payloads into orbit are impressive. Recently, the private sector has risen to the challenge, and Jeff Bezos's Blue Origin project (see p.309), whose staff includes several former DC-X engineers, has carried out a successful test flight.

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The Shenzhou spacecraft shares its three-part layout with the Russian Soyuz capsules, but is somewhat larger and has on extra pair of solar arrays on the orbital module.

20 November 1999

The unmanned Shenzhou 1 test rocket is successfully launched.

5 January 2003

The safe return of Shenzhou 4 after six days in orbit opens the way for a Chinese manned spaceflight.

15 October 2003

Yang Liwei becomes the first Chinese taikonaut, aboard Shenzhou 5.

16 October 2003

Shenzhou 5's re-entry module returns Yang to Earth after 14 orbits and

21 hours.

16 March 2004

Automated experiments in Shenzhou 5's orbital module end.

30 May 2004

The Shenzhou 5 orbital module burns up.

12 October 2005

Shenzhou 6 carries China's first two-man crew into orbit.

16 October 2005

The Shenzhou 6 re-entry module returns to Earth in Inner Mongolia.

15 April 2006

Experiments aboard the Shenzhou 6 orbital module are completed.

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