The space agency could decide as early as Friday whether to cancel, delay or proceed with plans to launch a nuclear-powered, SUV-size rover to the red planet.
NASA has already sunk $1.5 billion into the Mars Science Laboratory, which is pricier than expected. The mega-rover will roam the surface and drill into rocks for clues to whether the planet ever possessed an environment capable of supporting primitive life.
Doug McCuistion, who heads the Mars exploration program at NASA headquarters, told scientists in recent public meetings that he expects the mission's total cost to run over by more than 30 percent. If it goes over that threshold, Congress would have the right to intervene and use its power to end the project on its own.
Managed by NASA's Jet Propulsion Laboratory in California, the project has been plagued by development problems and ballooning costs that caught headquarters' attention. McCuistion told a gathering of Mars scientists last month that NASA was keeping a close eye on the project's progress and costs and participating in weekly reviews with JPL.
From the outset, the Mars Science Lab proved to be an engineering challenge due to its size and capability. The 9-foot-long robot geologist is bigger and can drive farther than its twin predecessors, Spirit and Opportunity, which are still alive after four years. It also carries some of the most sophisticated instruments, including a laser that can zap rocks from afar.
The mission's financial woes took many in the science community, who fear that other projects will suffer to pay for the mega-rover, by surprise.
"The magnitude of the increases has been mind-boggling," said geologist John Mustard of Brown University. "It has sent a shock wave to the Mars program and beyond to the planetary community."
If NASA pushes to launch in 2009 as planned, it will have to find the money to get the rover ready. Any delay until 2010 or 2011 will add at least $300 million to the mission's price tag.
Alex Dery Snider, a spokeswoman for the House Science Committee, said members were concerned about the extra cost and want to know how NASA will solve the problem.
Some scientists outside the Mars research community said canceling the project does not make sense as so much money has already been invested.
"We've got to continue our exploration of Mars, but in a way that's rational and sensible," said Frances Bagenal of the University of Colorado, Boulder.