Rockets that use charged particles to propel fast missions to Mars are one step closer, now a small-scale prototype has been demonstrated at full power.
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The ion engine may be used to maintain the orbit of the International Space Station within the next five years, and could lay the groundwork for rockets that could one day travel to Mars in about a month.
Since 2005, the Ad Astra Rocket Company of Webster, Texas, has been working to perfect a type of engine it calls VASIMR (Variable Specific Impulse Magnetoplasma Rocket).
It uses radio waves to heat argon gas, turning it into a hot plasma – a state of matter in which electrons are no longer bound to atomic nuclei. Magnetic fields then squirt the superheated plasma out the back of the engine, producing thrust in the opposite direction.
It shoots the propellant out at much higher velocity than conventional engines, resulting in far more acceleration per kilogram of fuel consumed.
In the near term, the company hopes to use a 200-kilowatt VASIMR engine to provide periodic boosts to the orbit of the International Space Station (ISS), which gradually drops in altitude due to atmospheric drag.
Now, the company has run such an engine at full power for the first time. On Wednesday, it ran its VX-200 engine at 201 kilowatts in a vacuum chamber in Houston, passing the 200-kilowatt mark for the first time.
"It's the most powerful plasma rocket in the world right now," says Franklin Chang-Diaz, the former NASA astronaut who heads the company.
The nearest thing to a competitor is NASA's 50-kilowatt Hall thruster, an engine based on accelerating electrically charged atoms, or ions, that the agency stopped developing in 2005 due to budget cuts.
Ad Astra has signed an agreement with NASA to test a 200-kilowatt VASIMR engine on the ISS in 2013. The company is talking to two space firms, SpaceX and Orbital Sciences, about the possibility of delivering the engine to the ISS on one of their launch vehicles.
If the tests go well, the company hopes to offer regular boosts to the space station's orbit on a commercial basis starting the following year.
Previously, spacecraft – including Russian and European cargo ships – have provided these boosts by firing their engines while docked with the space station.
But with conventional thrusters, the boosts consume 7.5 tonnes of propellant each year. VASIMR could do the same job with just 0.3 tonnes of argon per year, Chang-Diaz says. Since it is expensive to launch fuel into orbit, that could save millions of dollars per year, he says.
The revenue generated by the ISS boosts would help the company "make the technology better and enable human missions to Mars", Chang-Diaz told New Scientist.
A 10- to 20-megawatt class VASIMR engine could propel human missions to Mars in as little as 39 days, he says, compared to the six months or more required with conventional rockets.
The shorter trip would reduce astronaut exposure to space radiation, which could otherwise be a major barrier for human missions to Mars, especially given signs that radiation levels may be particularly high in coming decades.
Propelling fast trips to Mars may one day be very profitable for the company, says Chang-Diaz. "But for now, profit is not at Mars, it's closer to Earth," he says.