NASA Srhythm transport operated in low Earth orbit for 30 years before retiring in 2011. However, the U.S. space agency replacement for this vehicle, Orion, returned to the conical capsule design familiar from the Apollo missions. This was because NASA intended this newer craft 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 2010the US Space Force (and previously the US Air Force) was launching a robotic space plane called the X-37B in low Earth orbit on classified missions. China has its own military space plane called Shenron.
This year a test flight of the Sierra Space company plane could take place dream Catcher – 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.
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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 re-enters the atmosphere, increasing the area of Earth’s surface where it is possible to land from a specific re-entry 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.
There has been interest in spaceplanes since the early days of human spaceflight. A military space plane project called Dyna-Soar it was started in the US in 1957 and canceled shortly after construction began. The vehicle was sophisticated for the time, built with 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 than it was and has greater reuse but it turned out that extensive refurbishment was required between launches. 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 planeand Japan, with the HOPE vehicle. Both shows were canceled largely due to cost. The Soviet Union developed its own space shuttle-like vehicle called Buranwhich 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, are heated to more than a thousand degrees Celsius while traveling 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.
Even so, the expected temperatures experienced by the spacecraft could still reach 1,600 degrees C, necessitating a thermal protection system on the outside of the vehicle. The TPS space shuttle it included specially heat-resistant ceramic coatings and a reinforced carbon-carbon matrix capable of withstanding temperatures of up to 2,400 degrees C.
O loss of space shuttle Columbia during reentry in 2003, causing the deaths of seven astronauts, was the result of a TPS breach at the wing tip. 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 spaceplanesas well as systems that monitor TPS performance in real time.
There are currently two spaceplanes in operation, one Chinese and one American, that can reach orbit. Little information is available about Shenron from China, but the US military’s X-37B is better known. Weighing around five tons at launch, the nine-meter-long uncrewed 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 shuttle-like tiles on the lower surface as a lower-cost alternative to reinforcement 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 parts that protect the Dream Chaser are made of silica and each has a unique shape corresponding to the area of the vehicle they were designed to protect.
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 such as 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 computer 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.
Oluwamayokun AdetoroSenior Professor, Mechanical and Aerospace Engineering, Brunel University of London It is James CampbellReader, Brunel University of London. This article was republished from The conversation under a Creative Commons license. Read the original article.