By Eric Hand of Nature magazine

Dragon, the privately built space capsule intended to haul cargo and astronauts to the International Space Station (ISS), is auditioning for another high-profile role. Its maker, SpaceX of Hawthorne, California, says that the capsule, which is set to make its first test flight to the ISS later this month, could be dispatched to Mars--drastically cutting the cost of exploration on the red planet. Together with researchers at the NASA Ames Research Center in Moffett Field, California, the company is working on a proposal for a first 'Red Dragon' mission.

In a presentation at a meeting of NASA science advisers in Washington DC on October 31, the group advocated repurposing Dragon and the SpaceX Falcon 9 launch rocket to send an ice drill that would look for life near the poles of Mars. The mission could launch as early as 2018 for a cost of $500 million, proponents say--well within the budget of NASA's least-expensive class of planetary missions.

"These are initial ideas," says James Green, head of NASA's planetary-science division, who invited the presentation. Although NASA officials are cautious, the fact that the proposal was presented at all is telling in a time of tightening budgets.

Christopher McKay, principal investigator at Ames for the Mars proposal, called 'Icebreaker', says that the mission would target polar terrain where ice is present near the surface, similar to that probed by the Phoenix spacecraft in 2008. Capable of piercing Martian permafrost a metre thick, the robotic drill would retrieve samples for an onboard lab that would look for DNA and enzymes.

The most challenging part of any Mars mission is taking a spacecraft through the Martian atmosphere at high speed and then slowing it down to a soft landing. Proponents of the Red Dragon concept say that this could be done using the eight small rocket motors that will be added to the capsule for escape from the Falcon 9 rocket--a requirement for carrying humans, in case of an aborted launch. These motors would slow the capsule's descent and allow it to land tail-first, says John Karcz, a space scientist at Ames who is leading NASA's evaluation of the concept.

Scott Hubbard, an aeronautical engineer at Stanford University in California and a former Ames director, is sceptical, questioning whether the retro-rockets alone could decelerate the capsule. All previous Mars landers have used parachutes. He notes that a capsule designed to operate near Earth will need extensive changes to cope with the communications challenges and temperature extremes in interplanetary space. "All space is not the same, and deep space is quite different."

Yet the prospect of a fast, cheap route to the red planet could be attractive for Mars scientists, whose other plans are falling foul of budget constraints. Another mission proposed for 2018, a rover that would gather rocks in the first part of a three-stage effort to bring samples back to Earth, would cost $2.5 billion--a figure that NASA hopes to split with the European Space Agency. But that hasn't been enough to placate US President Barack Obama's budget advisers, who are wary of the $8.5-billion total cost of the multi-launch project and are threatening to leave the missions out of future budget requests.

McKay says some colleagues are fretting that Red Dragon will undermine the push for the 2018 rover mission. "I can see how some people would see that as threatening," he says, but adds that if Red Dragon ends up as the cheapest way to Mars, it should get a fair hearing. He says that Ames and SpaceX will refine the proposal in preparation for a planetary-mission competition that could begin in 2013.

This article is reproduced with permission from the magazine Nature. The article was first published on November 7, 2011.