It has always been difficult to make the first step off Earth and into space.
It’s easy on the moon, with its one-sixth gravity. Charlie Duke and his colleague aboard their tiny Apollo lunar module were able to return to lunar orbit with an engine and fuel tanks you could have fitted in a camper truck. By comparison, to climb out of Earth’s gravity well, the space shuttle stack was over fifty metres tall and weighed around two thousand tonnes, most of which was fuel, and oxidiser to burn that fuel. If Earth’s gravity was just a little stronger, in fact, no chemical-fuel rocket system like the shuttle would be able to escape from Earth. And if not for the pressure of military requirements which drove the development of rocketry, we might never have reached space at all; the first astronauts and cosmonauts rode into orbit on converted ballistic missiles.
The space shuttle worked, flying for three decades, despite the design flaws that led to two terrible accidents. But now the programme has been cancelled. And in February 2010 President Obama also dropped funding for NASA’s follow-up “Constellation” programme, which would have replaced the shuttle with a new range of human-rated rockets and spacecraft. The hope is that private industry will step up to the plate with a replacement launch system. Obama’s intention is evidently that the money freed up by not having NASA develop its own vehicles will help prime the pump for a new age of access to space. But for now it looks as if U.S. astronauts will have to hitch rides to orbit on Russian rockets.
Space is an expensive business, however, especially as a start-up. There’s a saying in the business that you need to spend billions to make millions out of space. But there are individuals with such means, and a drive, it seems, to make childhood ambitions come true. Companies like SpaceX and Blue Origin are rushing to develop their own launch systems capable of taking humans safely to orbit. NASA would be a customer, as would companies like Virgin Galactic, with its plans to take passengers on hops into space. SpaceX was established by South African dotcom entrepreneur Elon Musk, one of the creators of Paypal, and Blue Origin was founded by Jeff Bezos, the president of Amazon. This is new money being leveraged to achieve old dreams.
However, while the money might be new many of the designs are relatively conservative: capsules launched aboard chemical-rocket firecrackers, just like Apollo. Even the space shuttle had bits that were either discarded, like the external fuel tank, or had to be fished out of the ocean and rebuilt, like the solid rocket boosters.
What we need is not another throwaway rocket system. What we need is a true spaceplane. What we need is Avatar’s Transatmospheric Vehicle Valkyrie.
The space shuttle was boosted by rockets to orbit, but then could only glide back to Earth, unpowered. A true spaceplane would be capable of taking off unaided from a runway like a conventional aircraft, reaching orbit, and then returning to land. (In the industry jargon this is SSTO—single stage to orbit.)
This is an old dream. Before the development of Project Apollo the U.S. Air Force dreamt of spacecraft with wings. It flew the famous X-15 rocket plane, and it funded extensive research into “lifting bodies,” capable of very high-speed flight. Some of this research fed into the space shuttle programme, and today the USAF is experimenting with a scaled-down spaceplane known as the X-37B.
There are technologies on the horizon that could be developed to achieve a true SSTO craft. One promising technology is the “scramjet”: a supersonic combustion ramjet, which would enable aircraft to reach extremely high speeds within the atmosphere. A conventional “ramjet” draws in air to collect oxygen with which to burn its fuel, but the airflow within the engine is subsonic (below the speed of sound), so if the craft itself is travelling faster than sound, the intake of air has to be slowed down, creating drag. But in a scramjet the air passing through the engine can be supersonic—faster than sound, inside the engine itself. This enables the aircraft itself to reach much faster speeds.
The fastest air-breathing aircraft to date is NASA’s X-43A which has reached Mach 9.8 (that is, 9.8 times the speed of sound) using scramjet technology. In theory it is believed that scramjets could reach almost orbital velocity (which is Mach 25). The great advantage is in weight savings; unlike a rocket such as the space shuttle, a scramjet would need to carry virtually no oxidiser to burn its fuel, extracting it all from the air.
This is how the Valkyrie flies. Four times the size of the space shuttle, with its black heat-resistant tiles and white insulation reminiscent of the shuttle’s bodywork, the Valkyrie returns from orbit using friction with the atmosphere to brake, like the shuttle, and glides most of the way home. But to return to orbit it uses air-breathing turbojet engines to get off the ground, and switches to a scramjet mode at three times the speed of sound. It has rocket engines for the final burn to orbit. All this is powered by a fusion engine.
A compromise design with some potential is Skylon, being developed by a company called Reaction Engines Ltd based in Bristol, UK. Skylon’s engine works like a conventional jet up to five times the speed of sound at twenty-six kilometres altitude, at which point the air inlets close and the engine switches to an internal liquid oxygen supply, working as a rocket to complete the climb to orbit. As of February 2009, ESA, the European Space Agency, announced that it was funding a million-euro development of the engines.
Perhaps when the new private spacecraft start flying we will find ourselves on the verge of a new transport boom, like the spread of the railways in the nineteenth century. Aside from access to orbit, spaceplanes could be used for suborbital hops, such as a two-hour flight from New York to Sydney.
And, I suppose, other applications could be military, as we see in Avatar. Valkyrie-class vehicles acting like sub-orbital C-130s could deliver troops and materiel to combat zones anywhere in the world within hours.
But even if we do start getting into space at some reasonable price—so what? If you’re a budding space prospector, a proto-RDA, what are you supposed to be mining, the vacuum? As we’ve seen, in the wake of the Apollo missions scientists believed that even the closest destination, the moon, entirely lacked the most basic resource, water.
It turns out, though, that they might have been too hasty. And beyond the moon, the sky seems to be full of riches.