US space agency officials will make a seventh attempt to contact the Mars Polar Lander (MPL) on Monday night, and if that fails have only faint hopes of ever being able to contact the Lander.
"We're pretty much reaching the point where we've used up our final silver bullets," the mission's project manager Richard Cook told a press conference late Sunday.
The seventh attempt will be the last attempt with any "high probability" of success, Cook said. If that attempt fails, NASA will resort to attempting to put the Lander's systems into neutral, or "safe mode," sending the command via the Mars Global Surveyor Satellite, Cook said.
Late Tuesday, NASA will then attempt to boot up the Lander's systems from safe mode. However Cook emphasized that there are no strong expectations that this last-ditch course of action will prove successful.
NASA will however continue for "a couple of weeks" to listen out for any signal transmitted back via the satellite, Cook said, adding "the team is working on other possibilities."
The sixth attempt to achieve contact with the 165-million-dollar spacecraft failed on late Sunday.
MPL and its 30-million dollar Deep Space Two mini-probes, are thought to have touched down near Mars' South Pole mid-Friday in search of subterranean water. However, they never called home.
The mini-probes, which were to have split off from the Lander, also have been silent.
The Lander and its mini probes were launched on January 3, in order to fly to Mars' south pole to collect data on any water and gases there.
NASA only knows for certain that the Lander was functioning normally when it entered Mars' atmosphere at the spot the agency had targeted. It is believed to have touched down Friday about 800 kilometers (500 miles) from the planet's South Pole.
NASA scientists over the weekend thought they had the communications problem beat when they attempted to send signals to the Lander indirectly, using a broader antenna to send signals via the Mars Global Surveyor satellite which has been orbiting the planet since 1997.
But repeated attempts to communicate via this route proved fruitless.
One of the explanations for the Polar Lander's failure to contact its handlers could be that the spacecraft never separated from its heat shield and Deep Space Two's mini-probes, named after Antarctic explorers Scott and Amundsen.
The technical problems are another blow to the US space agency. NASA was eager to have a successful Mars mission after the loss of the 125-million-dollar Mars Climate Orbiter in September, due to a human error in calculating distances.
Since 1960, there have been 33 missions to fly by, orbit or land on Mars, but nearly two-thirds of them have ended in a major failure of some kind.
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