The trouble with exploring the solar system is that there just aren't any rocket fuelling stations out there.
That won't be the case if future planet-hopping astronauts are equipped with a new kind of rocket engine that burns two gases already in good supply on several other planets: methane and oxygen.
Methane doesn't exactly have high-tech, Trekkie credentials, being better known for its association with flatulent cows and natural gas.
But the latest tests of a prototype supersonic methane rocket engine by US-based XCOR Aerospace show that methane has interplanetary potential.
"It's not as nice as kerosene," says XCOR Aerospace's Aleta Jackson. "But it's available on Mars and other parts of the solar system."
That abundance on other worlds is crucial if spacecraft are ever going to break free of dependence on Earthly fuels and still travel at speeds that will get them to other planets in a timely fashion.
The 5M15 engine works by combining liquid oxygen with liquid methane to burn at supersonic speeds and generate 3400 kilograms of thrust. Most rockets use liquid oxygen and hydrogen, or solid fuels.
The real question, though, is why it has taken rocket scientists so long to discover the benefits of the most common hydrocarbon in the solar system, says Terri Tramel, project manager at NASA's Marshall Space Flight Center.
Besides having been detected in the Martian atmosphere, methane is known or suspected to exist on Saturn's moon Titan, Jupiter and other worlds.
Methane is also safer for humans, as centuries of farmers can attest, whereas many rocket fuels are quite toxic.
Another advantage is the higher temperatures at which methane is a liquid. Hydrogen used to launch the space shuttle needs to be kept at -253°C, whereas methane is liquid at -162°C.
Tested in the desert
The good news is that the tests of the prototype engine in California's Mojave Desert demonstrate that a methane rocket engine is feasible.
The next step will be to improve on the engine so it can cool itself and operate longer without overheating.
After that, Alliant Techsystems, which is overseeing XCOR Aerospace's work for NASA, will be designing a lighter-weight version of the gas rocket that would be more practical for spaceflight.
Recent tests show a narrow blue flame shooting several metres from the engine, which was attached to a concrete pad. The long flame was punctuated by bright spots called shock diamonds.
These are caused by the exhaust gases, which are travelling at three or four times the speed of sound, expanding and then being pressed back together by the pressure of Earth's atmosphere, Jackson explains.
In space the fiery exhaust would spread out more quickly, making more of an umbrella of hot gas, she says.
Source:
http://www.abc.net.au/science/news/stories/2007/1932305.htm
