NASA noted that if scientists can't reestablish communication with the rover before the Martian spring ends on the southern part of the planet in mid-March, the chances of reviving the robot will only diminish as the temperature drops.
"The amount of solar energy available for Spirit is still increasing every day for the next few months," said Mars Exploration Rover Project Manager John Callas. "As long as that's the case, we will do all we can to increase the chances of hearing from the rover again."
Last spring, scientists at the space agency reported that they had decided that the robotic machine had entered into a low-power hibernation mode, where most functions had ceased to conserve valuable, and dwindling, energy.
Spirit, which had been roaming the surface of Mars and sending information back to Earth for more than five years, had fallen on tough times.
The rover got into trouble last year when its wheels broke through Mars' crusty surface and got stuck in soft, salty sand underneath. For months afterward, NASA engineers worked to find a way to extricate the rover from the sand. But with two immobile tires on one side, scientists last January proclaimed it permanently stuck.
Spirit needs to be able to use solar energy to heat itself enough to make it through the frigid winter. NASA engineers tried to angle the vehicle's solar array so it's pointing more toward the sun. However, if blowing sand and debris cover the solar arrays, they won't be able to absorb enough energy to wake up the machine and run its few instruments.
Spirit's robotic twin, Opportunity, has faired better. Last winter, NASA scientists uploaded artificial intelligence software to Opportunity that enables the robot to make some of its own decisions. The rover now can decide on its own whether it wants to stop and analyze rocks spotted during its travels across the Martian surface.
The space agency noted that the upgrade will provide a good test of robotic autonomy, which it hopes to use more fully in future NASA space missions.
The robots are among the most advanced technology ever built at NASA's Jet Propulsion Lab, said Bruce Banerdt, a project scientist for the Mars Exploration Rovers, in an earlier interview.
When Spirit and Opportunity landed on Mars in 2004, they were both expected to work there for three months. Spirit worked for more than five years and Opportunity is still working.