NASA's Spirit rover has stopped transmitting data back to Earth -- a development that Jet Propulsion Laboratory engineers described as a "very serious anomaly" possibly caused by a simple software glitch or a potentially fatal hardware malfunction.
Spirit, which had performed flawlessly since its Jan. 3 touchdown on Mars' Gusev Crater, had sent back a beep Wednesday morning acknowledging that it had received a set of commands from mission controllers on Earth.
But the rover failed to return data about its overnight status that engineers had expected to receive.
Similarly, when the Mars Odyssey orbiter passed over the rover several hours later Wednesday, it was able to communicate briefly with the rover, but it too did not receive any data.
In essence, the orbiter received only "pseudo-noise," consisting of random digital ones and zeros, indicating that the transmitter was working but that the on-board computer was not providing any information for it to transmit, said deputy mission manager Richard Cook.
The rover skipped two other opportunities for communicating with Earth before responding Thursday morning to JPL engineers in Pasadena, who were able to communicate briefly using the craft's low-gain antenna. The craft automatically shifts to this antenna and transmits on a different radio frequency when its on-board sensors detect a problem.
The rover is also supposed to transmit the nature of the problem, but it has not yet done so, officials said.
Spirit's communications breakdown sent engineers at JPL into a feverish search for answers. The rover team began examining failure scenarios for the craft without much success.
The team attempted to replicate the events leading up to the loss of communication by using a test rover in a Pasadena laboratory but were unsuccessful.
"There is no single fault that explains all these problems," said project manager Peter C. Theisinger.
If the lack of data is caused by a software error -- which the team believes is the most probable source of the problem -- engineers are confident that they can rectify the matter and return the rover to normal operation, although the process may take several days.
Software or memory problems can be fixed with a software patch transmitted from Earth. Another possible solution is to simply reboot the rover's computer, just as earthbound PC users often do when confronting a malfunction.
