NASA’s space shuttle operated in low-Earth orbit for 30 years before its retirement in 2011. But the American space agency’s replacement Orion returned to the conical capsule design familiar from the Apollo missions.
This was because NASA intended it to be used for exploring targets in deep space, such as the Moon. Still, in recent years, we have seen a return to the spaceplane design.
Yet this year could see a test flight of the Dream Chaser, developed by American company Sierra Space. It would be the first commercial spaceplane capable of orbital flight.
If all goes well, the vehicle could be used to resupply the International Space Station with cargo and, eventually, crew.
Spaceplanes can fly or glide in the Earth’s atmosphere and land on runways rather than using parachutes. They are also more manoeuvrable as they reenter the atmosphere, increasing the area of the Earth’s surface where landing is possible from a specific re-entry point.
They also allow a gentler but longer flight path during re-entry and a softer landing, which is easier on crew and cargo than capsules. A runway also allows ground support crews and infrastructure to be ready at the landing location.
But spaceplanes are more complex and heavier than an equivalent capsule.
The winged body shape poses a challenge for designing thermal protection systems or TPS – the heat-resistant materials that protect the craft from scorching temperatures on re-entry. These additional costs mean it is impractical to design a spaceplane for a single flight.
They need to be used again and again to be viable.
Still, there has been interest in spaceplanes from the earliest days of human spaceflight. A military project called Dyna-Soar was started in the United States in 1957, then cancelled just after construction started.
The vehicle was sophisticated for its time, built using a metal alloy that was able to withstand high temperatures. It also featured a heat shield on the front that could be detached after it returned from space, allowing the pilot a clear view of the landing site.
The space shuttle, which entered service in 1981, was the first operational spaceplane.
It was supposed to launch more often than it did and have greater reusability, but it turned out that extensive refurbishment was required between space stints. It did, however, demonstrate the ability to return astronauts and large cargo from orbit.
The Soviet Union developed its own shuttle-like vehicle called Buran, which was successfully launched into space in 1988. The programme was cancelled after the collapse of the Soviet bloc.
Yet spaceplanes have specific requirements for the final part of their journeys. During atmospheric re-entry, they are heated to over 1,000 degrees Celsius as they travel at hypersonic speeds of over seven kilometres per second – more than 20 times the speed of sound.
A blunt nose design, where the edge of the spacecraft is rounded, is an ideal shape because it reduces the build-up of heat at the foremost part of the vehicle.
Even so, the expected temperatures experienced by the craft can still be as high as 1600°C, necessitating a thermal protection system on the outside of the vehicle.
The space shuttle TPS included ceramic tiles that were especially heat resistant and a reinforced carbon matrix that was capable of withstanding temperatures as high as 2400°C.
The loss of the Columbia shuttle during re-entry in 2003, causing the deaths of seven astronauts, involved a breach in the TPS on the leading edge of the wing.
This resulted from a piece of insulating foam flying off the external tank during Columbia’s launch and hitting the wing.
This foam issue was a problem with the shuttle because of the way it was launched on the side of the external propellant tank. The new craft will fly on top of conventional rockets, where falling foam is not a threat.
There are two operating spaceplanes – one is Chinese and the other is American – that can reach orbit. Little information is available on China’s Shenlong, but the US military’s X-37B is better known.
Weighing close to five tonnes at launch, the nine metre-long, uncrewed vehicle is launched using a conventional rocket and lands autonomously on a runway at the end of its mission.
The X-37 B uses tiles similar to the shuttle over the lower surface along with an alternative to reinforced carbon called Tufroc, developed for the nose and leading edges.
They should soon be joined by Dream Chaser, which was developed to carry both cargo and astronauts. NASA wants to prove its safety before carrying people by ferrying cargo to the space station first.
The ability to return comparatively fragile cargo to the surface because of a softer landing is a key capability. The tiles that protect Dream Chaser are made from silica, and each has a unique shape matched to the area on the vehicle they are designed to protect.
There is continued interest in spaceplanes because of their ability to return crew and cargo to a runway. The demand is limited now. But if the costs continue to fall and the industry expands, they will become an increasingly viable alternative to capsules.
In the long term, there is also potential for spaceplanes to reach orbit after taking off from a runway. The challenges of developing these single-stage-to-orbit (SSTO) vehicles are considerable.
But concepts such as Skylon are leading to technical advances that could eventually support the development of an SSTO craft.
Given that several governments, space agencies, and private companies worldwide are investing heavily in spaceplane research and development, we could see a future where flights become routine.
The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy of China Factor.