When Will Space Planes Take People to Other Planets?
For space planes to be efficient and powerful, they must weigh practically nothing
Technically, space planes have been around for a long time. The X-15 began flying in the late 1950s and the Space Shuttle, first flown in 1981, was certainly a space plane of sorts, and other less impressive ones have flown as well.
However, no space plane has been able to launch from the ground without external aid and then venture forth to the moon, the planets or beyond. Unfortunately, producing such a space plane is still science fiction, and it would be expensive to develop, make no mistake. But a flying machine with this capability would be very useful in the advancement of manned space exploration. Many people would pay lots of money to fly in such a space vehicle as well!
Let’s find out how long it will be before aerospace engineers develop the next generation of those powerful, elegant, winged spacecraft many people would love to see blasting into the sky, destination: Mars or Saturn.
History of Space Planes
The X-15 was the first operational space plane, because it could maneuver both in the air and space. First flown in 1959, the X-15 was a rocket glider launched from the underbelly of the B-52 Stratofortress. The X-15 could accelerate to about 4,500 miles per hour and attain an altitude of 50 to 70 miles. (By international standards, anything above 100 kilometers or 62.1 miles is considered the threshold of space.) At present, the X-15 is still the world’s fastest manned rocket-powered aircraft.
The next great leap for space planes came with the launch of America’s Space Shuttle in 1981. The Space Shuttle was big and bulky, requiring the use of external fuel tanks, but it could launch from the ground and obtain an orbital trajectory, while carrying a large payload and astronauts, thus making it the space workhorse of the United State from 1981 to 2011.
Please keep in mind, it’s one matter for a space plane to reach orbit but it’s another for the craft to survive the tremendous heat of re-entering the earth’s thick atmosphere. The Space Shuttle needed heat-resistant ceramic tiles to protect its underside from temperatures approaching 3,000 degrees Fahrenheit. The X-15, in comparison, had no such heat-resistant capability, so it was strictly a suborbital space plane.
During its time, the Space Shuttle was often called the most complicated machine in the world, a title it almost certainly deserved. Nevertheless, there were mishaps. Two flights ended in disaster, one during launch and the other during landing, the two most dangerous times for any space plane.
Then SpaceShipOne was launched in September 2004. It was the world’s first privately funded space plane. The craft was air-launched and suborbital in capability, reaching speeds of Mach 3, so its possibilities were limited (Mach 1 is 768 mph). After this flight, which earned the developers, Paul Allen and the company, Scaled Composites, $10 million for winning the Ansari X Prize, SpaceShipOne was retired to a museum.
Under current development by the Spaceship Company, owned by Virgin Atlantic, SpaceShipTwo has rocketed into the sky during test flights. Unfortunately, in October 2014 one such space plane broke up some 50,000 feet in the air and plummeted to earth. One pilot was killed and another was seriously injured. Nevertheless, the Spaceship Company plans to build five SpaceShipTwo space planes for the purpose of conducting commercial passenger flights. These vehicles could also carry scientific payloads for NASA and other organizations.
XCOR Aerospace Linx (or Xerus)
Under development since 2003, the XCOR Linx, is a proposed rocket-powered space plane that will supposedly takeoff from a runway, ascend to 100 km, and then return to earth and land on a runway. This vehicle is designed to carry a pilot, one passenger and scientific instruments.
The Air Force X-37B Space Plane
Perhaps the most advanced space plane at present is the Air Force X-37B mini shuttle (aka the Orbital Test Vehicle). This space plane is much smaller than the Space Shuttle and is launched from atop an Atlas V rocket. It can stay in orbit for months at a time and land horizontally as a glider. Unfortunately, the X-37 is an unmanned vehicle, uses conventional rocket technology and has a payload the size of a pickup truck.
Much about the X-37 is classified. It apparently operates as a reconnaissance space vehicle, but some think it may be used as a space weapon. Whatever its usage, the X-37 certainly has its limitations, though theoretically it could one day carry astronauts into space.
China’s Proposed Space Plane
Reportedly, China’s is working on a space plane that, when built and operational, would make it the leader in the development of such marvelous vessels. Billed as a hypersonic space plane, this envisioned space plane could take off from a runway and eventually soar into low earth orbit. Built by the China Aerospace Science and Technology Corporation, this hybrid space plane would use a series of four propulsion systems. The first, a turbofan or turbojet engine, would thrust the craft horizontally and then upward from a runway. Once in flight, the craft would shift to ramjet propulsion and then, when it reaches sufficient velocity, a scramjet engine would then push it into hypersonic flight some 50 to a 100 miles up. In the last phase of this hypothetical voyage, a conventional chemical rocket would propel the space plane into low earth orbit.
Unfortunately, if China’s space plane, a very complex machine indeed, ever flies, it will have to carry thousands of pounds of fuel in order to reach even low earth orbit, and therefore will probably have little if any payload. Presumably, it will carry an astronaut or two, but that will be about all. At any rate, its first flight probably won’t be until the middle 2020’s at the earliest.
The Biggest Problem for Space Planes
In the 1980s, the Reagan administration envisioned the development of an “Orient Express,” which could fly from New York to Tokyo in two hours, flying at Mach 25. Well, this marvelous vehicle remained little more than theoretical. Then in the middle 1990s the Clinton administration wanted to build a national aero-space plane, one surpassing the limitations of the Space Shuttle at the very least, but the technology simply wasn’t available.
The critical problem with producing a space plane that takes off from the ground without the use of external fuel tanks and then flies into orbit or beyond is that it must have a very powerful propulsion system and also weight practically nothing. For perspective, it takes 60 times more energy to propel a vehicle into orbit than it does to accelerate one to Mach 3, the top speed for many jet fighters.
The only propulsion system available at present for use in space planes is chemical rockets similar to those used by the Space Shuttle. These rockets produce great thrust but also use massive amounts of fuel, which adds much weight to the craft. The fuel tanks weigh a lot too.
One option is that while this proposed space plane flies through the atmosphere it could take advantage of an air-breathing engine such as the scramjet, the existence of which has been around since the 1950s (a version of the X-15 was proposed to use one). The scramjet operates at supersonic speeds and can theoretically accelerate an aircraft from Mach 12 to 24. (Earth Escape Velocity is Mach 33 or 25,000 mph.) However, in order for a scramjet to operate efficiently, the space plane must first be accelerated to hypersonic speeds with the use of a turbojet, turbofan or rocket. Unfortunately, this arrangement is complicated and heavy and would only work in the atmosphere.
The Future of Space Planes
Here’s a pertinent quote from the website www.space.com: “Some of it is pop culture – things like Buck Rogers – but we see this space plane concept throughout history,” says Roger Launius, space history curator at the Smithsonian’s National Air and Space Museum. “We have this longstanding belief that coming back on wings, and using wings for flying into space, is the right way to go, and we haven’t abandoned that yet.”
Indeed, many haven’t abandoned that belief. The future is where the space plane’s development lies, because it obviously needs a revolutionary new propulsion system. Chemical rockets are strictly “old tech” and decidedly twentieth century. Humankind doesn’t need another Space Shuttle; it needs imagination, advanced engineering and almost certainly a fair amount of cash.
Well, what futuristic propulsion system could be used for the next generation of space planes? One possibility would be using an engine that runs on antimatter. A so-called positron reactor could propel the space plane much faster than chemical rockets, and the fuel would weigh milligrams rather than the thousands or millions of pounds needed for a comparable amount of thrust from chemical rockets. The NASA Institute for Advanced Concepts is working on this positron reactor engine. Let’s hope we see a prototype soon!
Other possibilities would be nuclear propulsion, a hydrogen reaction engine or even antigravity, but clearly something else will be needed to power future space planes – the ones many people envision, the ones they want to see soaring through the sky, destination the moon or Mars - something like the proverbial flying saucer perhaps.
Unfortunately, that space plane probably won’t be developed for many years - unless, of course, more money is spent on development. Will the people open their wallets? We could build one within years!
Well, maybe we could or couldn’t, but Roger Launius and other experts believe space planes will definitely be a major aspect of future space exploration. After all, there’s nothing more beautiful than a sleek, winged space vehicle. Who wouldn't want to fly in one of those?
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© 2012 Kelley