Replacing chemical rockets with electric motors could cut the 6 month travel time between Earth and Mars by 75%. A company called Ad Astra has successfully tested a 200 Kw proto-type electro-magnetic thruster at full power and says a 20-megawatt engine could propel human missions to Mars in just 39 days.
A VAriable Specific Impulse Magnetoplasma Rocket (VASIMR) sometimes referred to as Electro-thermal Plasma Thruster or Electro-thermal Magnetoplasma Rocket, capable of reaching speeds of up to 126,000 miles per hour, uses radio waves to ionize and heat a gas such as argon, xenon, or hydrogen to 51.8 million degrees Fahrenheit (11 million degrees Celsius) contained and directed by a magnetic field to accelerate the resulting plasma and generate thrust.
We've had a look at Plasma Jet Engines possibly replacing fossil fueled jet turbines in commercial aircraft and it seems Plasma motors are the preferred option for NASAs future propulsion systems. Although a VASIMR is not suitable to launch payloads from the surface of the Earth due to its low thrust to weight ratio, they are well suited to act as an upper stage and can reduce the fuel requirements for in-space transportation, in some applications they are one-twentieth the cost of operating chemical rockets.
As with a Plasma Jet Engine, the electrical power source may be a challenge. As a station keeping motor on the International Space Station (ISS) the VASIMR could maintain the ISS's orbit without requiring any additional fuel as the motor would be powered by the Stations solar panels and use hydrogen as the propellant gas which is already generated as a waste product on the Station.
While the 200-kilowatt prototype VASIMR engine will suffice for ISS station keeping, the distance between the Earth and Mars varies between 35 and 250 million miles (55 million and 400 million kilometers) depending on their points of orbit, so a 20-megawatt plasma rocket is required for a human flight to Mars. Solar isn't really an option at these power levels. The entire solar array on the ISS generates 120 kW. Using Solar to generate 20 MW would require an array 160 times the size and it would produce less energy as the spacecraft traveled further away from the sun so the only option is a Nuclear power source.
The VASIMR is expected to be put to work on the ISS for orbit re-boosting duty in late 2013 or early 2014.
Ad Astra Rocket Company
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