Future Mars outposts or colonies may seem more distantthan ever with NASA?s exploration plans in flux, but the rocket technology thatcould someday propel a human mission to the red planet in as little as 40 days mayalready exist.

A company founded by former NASA astronaut FranklinChang-Diaz has been developing a new rocket engine that draws upon electricpower and magnetic fields to channel superheated plasma out the back. Thatstream of plasma generates steady, efficient thrust that uses low amounts ofpropellant and builds up speed over time.

"People have known for a long time, even back in the'50s, that electricpropulsion would be needed for serious exploration of Mars," said TimGlover, director of development at the Ad Astra Rocket Company.

The rocket technology could drastically cut down theamount of time a spacecraft needs to send astronauts on Marsmissions. Instead of half a year, a spacecraft could make the trip in justover a month using the engine and a large enough power source, according to anAd Astra mission study.

NASA's recentcourse change has freed up some funding for new propulsiontechnologies. 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 lastmonth.

"While we cannot provide a date certain for thefirst human visit, with Mars as a key long-term destination we can identifymissing capabilities needed for such a mission and use this to help define manyof the goals for our emerging technology development," Bolden said.

Familiar chemical rockets that burn solid or liquidchemical propellants won't get humans to Mars fast because they would requiretoo much propellant. They can create a huge boost for several minutes at thecost of huge inefficiency ? not unlike a speed demon with poor gas mileage.

Slow but steady push

Some satellites and spacecraft already rely upon electricpropulsion in their ion engines that create thrust based on energizedgas. Similarly, Ad Astra's Variable Specific Impulse Magnetoplasma Rocket(VASIMR) ionizes gases such as xenon or hydrogen to create superheated plasmastream for thrust.

But VASIMR also has the advantage of relying uponelectromagnetic waves to create and energize the plasma, rather than physicalelectrodes that get worn down due to contact with the superheated plasma. Thattranslates into greater reliability over time and allows for a very denseplasma stream to create more thrust.

VASIMR can also adjust its thrust to speed up or slowdown, and even has an "afterburner" mode that provides a temporaryhigh-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 athigh power levels."

Yet even the most efficient rocket engine needs a powersource. VASIMR may use gas as the propellant, but it also requires an electricpower source that can ionize the gas to create its plasma.

I need more power!

A mission trajectory study estimated that a VASIMR-poweredspacecraft could reach the red planet within 40 days if it had a200 megawatt power source. That's 1,000 times more power than what the currentVASIMR prototype will use, although Ad Astra says that VASIMR can scale up tohigher power sources.

The real problem rests with current limitations in spacepower sources. Glover estimates that the Mars mission scenario would need apower source that can produce one kilowatt (kW) of power per kilogram (kg) ofmass, or else the spacecraft could never reach the speeds required for a quicktrip.

Existing power sources fall woefully short of that ideal.Solar panels have a mass to power ratio of 20 kg/kW. The Pentagon's DARPAscience lab hopes to develop solar panels that can achieve 7 kg/KW, and stretchedlens arrays might reach 3 kg/KW, Glover said. That's good enough for VASIMR totransport cargo around low-Earth orbit and to the moon, but not to fly humansto Mars.

Ad Astra sees nuclear power as the likeliest power sourcefor a VASIMR-powered Mars mission, but the nuclear reactor that could do thejob remains just a concept on paper. The U.S. only ever launched one nuclearreactor into space back in 1965, and it achieved just 50 kg/kW.

A way forward

VASIMR and the necessary power sources could get a boostin the coming years. NASA's new five-year budget includes more than $3 billionfor developing heavy-lift and propulsion technologies, as well as a GameChanging Innovation program that similarly targets next-gen propulsion andpower sources.

The U.S. space agency's new chieftech guru has also emphasized propulsion as a critical area, underNASA's new Space Technology program.

"The budget's emphasis on developing advancedtechnologies to make space exploration easier and cheaper is very encouragingto us," Glover noted.

VASIMR reached a milestone late last year by achieving200 kilowatts of power with the VX-200 prototype. Since then, Ad Astra has workedon the flight-capable VF-200 version that could undergo testing at theInternational Space Station (ISS) within the next several years.

As for getting VASIMR into space, Ad Astra has discussedpossible launch options with commercial spaceflight providers.

"Anybody who wants to send anything to ISS after theshuttle retires is talkingwith SpaceX, and Orbital Sciences," Glover said.