By Jeremy Hsu
SPACE.com Contributor
posted: 05 March 2010
01:08 pm ET
Future Mars outposts or colonies may seem more distant than ever with NASA's exploration plans in flux, but the rocket technology that could someday propel a human mission to the red planet in as little as 40 days may already exist.
A company founded by former NASA astronaut Franklin Chang-Diaz has been developing a new rocket engine that draws upon electric power and magnetic fields to channel superheated plasma out the back. That stream of plasma generates steady, efficient thrust that uses low amounts of propellant and builds up speed over time.
"People have known for a long time, even back in the '50s, that electric propulsion would be needed for serious exploration of Mars," said Tim Glover, director of development at the Ad Astra Rocket Company
The rocket technology could drastically cut down the amount of time a spacecraft needs to send astronauts on Mars missions. Instead of half a year, a spacecraft could make the trip in just over a month using the engine and a large enough power source, according to an Ad Astra mission study.
NASA's recent course change has freed up some funding for new propulsion technologies. And the U.S. space agency has not lost sight of the red planet, NASA administrator Charles Bolden told Congress as he presented a new budget last month.
"While we cannot provide a date certain for the first human visit, with Mars as a key long-term destination we can identify missing capabilities needed for such a mission and use this to help define many of the goals for our emerging technology development," Bolden said.
Familiar chemical rockets that burn solid or liquid chemical propellants won't get humans to Mars fast because they would require too much propellant. They can create a huge boost for several minutes at the cost of huge inefficiency — not unlike a speed demon with poor gas mileage.
Slow but steady push
Some satellites and spacecraft already rely upon electric propulsion in their ion engines that create thrust based on energized gas. Similarly, Ad Astra's Variable Specific Impulse Magnetoplasma Rocket (VASIMR) ionizes gases such as xenon or hydrogen to create superheated plasma stream for thrust.
But VASIMR also has the advantage of relying upon electromagnetic waves to create and energize the plasma, rather than physical electrodes that get worn down due to contact with the superheated plasma. That translates into greater reliability over time and allows for a very dense plasma stream to create more thrust.
VASIMR can also adjust its thrust to speed up or slow down, and even has an "afterburner" mode that provides a temporary high-speed boost at the cost of efficiency.
"Our technology is different," Glover told SPACE.com. "It's one possibility. We certainly think it has the most potential at high power levels."
Yet even the most efficient rocket engine needs a power source. VASIMR may use gas as the propellant, but it also requires an electric power source that can ionize the gas to create its plasma.
I need more power!
A mission trajectory study estimated that a VASIMR-powered spacecraft could reach the red planet within 40 days if it had a 200 megawatt power source. That's 1,000 times more power than what the current VASIMR prototype will use, although Ad Astra says that VASIMR can scale up to higher power sources.
The real problem rests with current limitations in space power sources. Glover estimates that the Mars mission scenario would need a power source that can produce one kilowatt (kW) of power per kilogram (kg) of mass, or else the spacecraft could never reach the speeds required for a quick trip.
Existing power sources fall woefully short of that ideal. Solar panels have a mass to power ratio of 20 kg/kW. The Pentagon's DARPA science lab hopes to develop solar panels that can achieve 7 kg/KW, and stretched lens arrays might reach 3 kg/KW, Glover said. That's good enough for VASIMR to transport cargo around low-Earth orbit and to the moon, but not to fly humans to Mars.
Ad Astra sees nuclear power as the likeliest power source for a VASIMR-powered Mars mission, but the nuclear reactor that could do the job remains just a concept on paper. The U.S. only ever launched one nuclear reactor into space back in 1965, and it achieved just 50 kg/kW.
A way forward
VASIMR and the necessary power sources could get a boost in the coming years. NASA's new five-year budget includes more than $3 billion for developing heavy-lift and propulsion technologies, as well as a Game Changing Innovation program that similarly targets next-gen propulsion and power sources.
The U.S. space agency's new chief tech guru has also emphasized propulsion as a critical area, under NASA's new Space Technology program.
"The budget's emphasis on developing advanced technologies to make space exploration easier and cheaper is very encouraging to us," Glover noted.
VASIMR reached a milestone late last year by achieving 200 kilowatts of power with the VX-200 prototype. Since then, Ad Astra has worked on the flight-capable VF-200 version that could undergo testing at the International Space Station (ISS) within the next several years.
As for getting VASIMR into space, Ad Astra has discussed possible launch options with commercial spaceflight providers.
"Anybody who wants to send anything to ISS after the shuttle retires is talking with SpaceX, and Orbital Sciences," Glover said.
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