An innovative plasma rocket being built as a spare for one heading to the International Space Station may have a space mission of its own: visiting an asteroid.
Equipped with an electric propulsion system, the rocket, known as Variable Specific Impulse Magnetoplasma Rocket (VASIMR), is being developed to one day transport astronauts to Mars in 39 to 45 days - a fraction of the six to nine months the trip would take with conventional chemical rockets.
Shorter travel time would greatly reduce astronauts' exposure to potentially deadly cosmic and solar radiation, currently a show-stopper for human missions to Mars.
Setting sail for an asteroid would be a powerful demonstration of VASIMR technology, which uses radio waves to ionise propellant - such as argon, xenon or hydrogen - and heat the resulting plasma to temperatures 20 times hotter than the surface of the Sun.
In place of metal nozzles to control the direction of the exhaust, VASIMR uses magnetic fields.
"All of a sudden, the future is here," says VASIMR inventor and physicist Franklin Chang-Diaz, a seven-time shuttle astronaut who left NASA in 2005 to start a company and work full time developing the rocket.
Chang-Diaz's Ad Astra Rocket Company, reached a significant milestone last year when it successfully operated a demonstrator VASIMR at full power in a vacuum chamber.
"The engine is actually firing right now," says Chang-Diaz. "We have lots of hurdles and challenges; we have lots of work to do. But if you look at what has happened in the last five years since we left NASA, it's been amazing."
Ad Astra plans to launch its flight version VASIMR to the space station in 2014. As a backup, Chang-Diaz intends to manufacture two engines in case a launch accident or other major problem prevents the first from reaching the outpost.
Once the engine is safely installed outside the station, the spare could be tapped for a new mission - one that did not require investment by NASA.
"I had this idea that maybe there's a way we can use this backup engine that he's already building," says Rob Kelso, a former shuttle flight director at NASA's Johnson Space Center in Houston now working to build innovative partnerships between NASA and commercial firms.
While the space station's VASIMR can draw power from the outpost, a free-flying engine will need its own source. As part of the proposed asteroid mission, NASA and Ad Astra would team with the Defense Advanced Research Projects Agency to use its super-efficient, 200-kilowatt solar array currently under development.
Once the rocket reached its target asteroid, the power would be available to operate science equipment and other gear.
"You could do an extraordinary mission," Chang-Diaz says. "You don't need the power system for the rocket. Once you're there, you turn off the engine and you have 200 kilowatts to do anything you want to do. You can do all kinds of unheard of things with that level of power."
In addition to radar mapping and surveys, the mission also could pick up a sample from the asteroid and return it to Earth. Scientists are interested in learning more about where asteroids came from, how they formed and whether they carry the ingredients for life. On a practical level, learning how asteroids are structured would be useful in case one is discovered to be on a collision course with Earth and needs to be moved.
The mission also fits with the new direction President Barack Obama has outlined for NASA. Obama wants to cancel the return-to-the-Moon program NASA had been developing and instead spend money on producing and testing new technologies for deep space exploration.
During a speech at Kennedy Space Center earlier this month, Obama specifically called for a human mission to an asteroid by 2025.
The VASIMR asteroid mission is among several proposals currently being assessed by a NASA study team. If selected, Kelso says, the mission could fly somewhere around 2017.