March 1, 2024

A new generation of space planes is taking advantage of the latest technology

NASA’s space shuttle operated in low-Earth orbit for 30 years before its retirement in 2011. However, the U.S. space agency’s replacement for this vehicle, Orion, returned to the conical capsule design familiar from the Apollo missions. This was because NASA intended this newer spacecraft to be used to explore deep space targets such as the Moon.

But in recent years, we’ve seen a comeback in spaceplane design. Since 2010, the US Space Force (and previously the US Air Force) has launched a robotic space plane called the X-37B into low Earth orbit on classified missions. China has its own military space plane called Shenron.

This year we will be able to witness a test flight of Sierra Space’s Dream Chaser – the first commercial space plane capable of orbital flight. If all goes well, the vehicle could be used to resupply the International Space Station (ISS) with cargo and, eventually, crew.

Space planes can fly or glide in Earth’s atmosphere and land on runways, rather than using parachutes to land on water or flat ground like capsules. They are also more maneuverable as the spacecraft reenters the atmosphere, increasing the area of ​​Earth’s surface where landing is possible from a specific reentry point.

Spaceplanes also allow for a smoother but longer flight path during reentry and a softer landing, which is easier on the crew and cargo than capsules, which can land with a thud. A runway also allows ground support teams and infrastructure to be ready at the landing site.

Cost and complexity

But space planes are more complex and heavier than an equivalent capsule. The shape of the winged body poses a particular challenge for the design of thermal protection systems (TPS) – the heat-resistant materials that protect the spacecraft from scorching temperatures on re-entry. These additional costs mean that it is impractical to design a space plane for a single flight. They need to be used repeatedly to be viable.

The US Space Force’s X-37B does not carry a crew and its missions are classified.
Staff Sgt. Adam Shanks/US Space Force

There has been interest in spaceplanes since the early days of human spaceflight. A military space plane project called Dyna-Soar was started in the US in 1957 and canceled shortly after construction began. The vehicle was sophisticated for the time, built from a metallic alloy capable of withstanding high temperatures and featuring a heat shield on the front that could be detached after returning from space, so that the pilot could see clearly during landing.

The space shuttle, which entered service in 1981, was the first operational space plane. It was supposed to be released more frequently and have greater reusability, but it turned out that extensive refurbishment was needed between releases. However, it has demonstrated the ability to return astronauts and large payloads from orbit.

Other space agencies invested in the 1980s and 1990s, in Europe, with the Hermes space plane, and in Japan, with the HOPE vehicle. Both shows were canceled largely due to cost. The Soviet Union developed its own shuttle-like vehicle called the Buran, which successfully flew into space once in 1988. The program was canceled after the collapse of the Soviet Union.

Feeling the heat

Spaceplanes have specific requirements for the final part of their journeys – when they return from space. During atmospheric reentry, they are heated to more than a thousand degrees Celsius as they travel at hypersonic speeds of more than seven kilometers per second – more than 20 times the speed of sound. A blunt nose design (where the edge of the spacecraft is rounded) is the ideal shape because it reduces heat build-up in the front of the vehicle.

Space Shuttle, STS-132
At launch, the space shuttle was attached to the side of a large external propellant tank.
NASA/JSC

Even so, the expected temperatures experienced by the vessel can still reach 1600°C, requiring a thermal protection system on the outside of the vehicle. The TPS shuttle included specially heat-resistant ceramic tiles and a reinforced carbon-carbon matrix capable of withstanding temperatures of up to 2,400°C.

The loss of the Space Shuttle Columbia during reentry in 2003, causing the deaths of seven astronauts, was the result of a wingtip TPS breach. This resulted from a piece of insulating foam that flew off the space shuttle’s external tank during Columbia’s launch and struck the wing.

This foam problem was recurring on the Space Shuttle due to the way it was launched on the side of the external propellant tank. But the latest spaceplane designs will fly on conventional rockets, where falling foam is not a problem.

An effective TPS remains vital to the future success of spaceplanes, as do systems that monitor TPS performance in real time.

Current vehicles

There are currently two spaceplanes in operation, one Chinese and one American, that can reach orbit. Little information is available about China’s Shenron, but the US military’s X-37B is better known. Weighing close to five tons at launch, the nine-meter-long unmanned vehicle is launched using a conventional rocket and lands autonomously on a runway at the end of its mission.

The X-37B’s TPS uses Space Shuttle-like tiles on the lower surface with a low-cost alternative to reinforced carbon-carbon called Tufroc, developed for the X37B, on the nose and leading edges.

They should soon be joined by the Dream Chaser, which was developed by the company to transport cargo and astronauts, but NASA wants to prove its safety before transporting people, using it first to transport cargo to the space station. The ability to return comparatively fragile payloads to the surface due to a softer landing is a key capability. The tiles that protect the Dream Chaser are made from silica and each has a unique shape that matches the area of ​​the vehicle they are designed to protect.

dream Catcher
Dream Chaser under evaluation at NASA’s Neil Armstrong Test Facility.
NASA

Future developments

There is continued interest in space planes due to their ability to return crew and cargo to the runway. Demand for this capacity is limited now. But if launch costs to space continue to fall and the industry’s expansion into space increases demand, they will become an increasingly viable alternative to capsules.

In the longer term, there is also potential for space planes capable of reaching orbit after lifting off from a runway. The challenges of developing these single stage to orbit (SSTO) vehicles are considerable. However, concepts like the Skylon vehicle are leading to technical developments that could eventually support the development of an SSTO spacecraft.

In the near future, spaceplanes appear promising for the following reasons: new design techniques, improved materials for the TPS, advanced computational modeling and simulation tools to optimize different aspects of design and flight parameters, and continuous improvements in propulsion systems.

Given that several governments, space agencies and private companies around the world are investing heavily in the research and development of spaceplanes, we could see a future where flights with these vehicles become routine.

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