Spirit’s Communication Breakdown

Spirit images lander
Before the recent communication glitch, Spirit's Panoramic Camera took a series of images of the lander, which were assembled into this near-true-color mosaic.
Courtesy NASA / JPL / Cornell University.
[Updated 10:05 a.m. EST, January 23] Mission controllers at the Jet Propulsion Laboratory are experiencing a potentially fatal communication problem with Spirit, and they don’t know why. Their mood is one of concern, but not panic. "We now know that we have had a very serious anomaly on the vehicle," said project manager Pete Theisinger (Jet Propulsion Laboratory) at a January 22nd press conference.

The problems began on January 21st, when Spirit stopped sending intelligible radio signals. Mission planners originally thought the problem was due to bad weather over the Deep Space Network (DSN) tracking station near Canberra, Australia. But they now realize the problem is on Mars, not Earth.

In the late evening of January 21st, Spirit radioed a random pattern of zeros and ones to NASA’s Mars Global Surveyor, currently orbiting the red planet, which then relayed the signals to Earth. Spirit was supposed to have transmitted science data as the orbiter flew overhead, and the signal was not only garbled but much shorter than anticipated. The pattern indicated that Spirit’s radio was functioning, but was not receiving data from the on-board computer.

Attempts to raise Spirit later on January 21st and early on the 22nd also failed, but mission engineers picked up a beep from Spirit around noon Eastern Standard Time (EST) on the 22nd, indicating that the rover had received a test transmission from Earth. But Spirit failed to call home when Mars Global Surveyor flew overhead late on the 22nd.

The situation has noticeably improved as of the morning of the 23rd. NASA's DSN tracking station near Madrid, Spain picked up a 10-minute transmission around 7:30 a.m. EST, but it was at a slow emergency rate of only 10 bits per second. The signal came during a communication window about 90 minutes after the rover woke up after sunrise. The team received a 20-minute data transmission an hour later at a rate of 120 bits per second.

"There is no one single fault that explains all the observables," says Theisinger. "If this problem on Spirit is somehow a software corruption issue or memory corruption issue, and there is not a serious power fault, then I think Spirit can go for quite a long time and we can pick up the pieces again. If on the other hand we’ve had some kind of major power fault, then it has life-limiting characteristics, of course, but it also might be more difficult to recover from that."

Deputy project manager Richard Cook (JPL) noted that several communication blackouts occurred during the Mars Pathfinder mission in 1997. Communicating with a lander on another planet is more difficult than a probe in deep space because a lander is out of contact on the planet’s far side half of the time, and it does not receive sunlight constantly to generate electricity. "We’re frequently having to tell the rover what to do without knowing what it’s state is or if it’s even listening to us," said Cook.

Theisinger dismissed the possibility that the interruption could be related to conditions on Mars, such as a dust storm: "We can’t conceive of a local environmental problem that would cause this. We designed for a very extreme environment, and if anything it has been more benign than that."

When Spirit fell silent it was sitting next to a rock known as Adirondack. Spirit’s cameras were about to take images, and its Mini-Thermal Emission Spectrometer was going to take data. Later in the day Spirit was scheduled to drill into Adirondack with its Rock Abrasion Tool.

The communications glitch comes at a time when many of the engineers are about to leave the Spirit team to prepare for Opportunity’s landing at 12:05 a.m. Eastern Standard Time on January 25th. Fortunately, all of the command sequences for entry, descent, and landing have been loaded into Opportunity’s computer, and it appears Opportunity is on course for its landing site in Meridiani Planum, meaning it’s unlikely any further rocket burns will be required. "These things are largely scripted, so there’s not a lot of interaction with the ground in those events," said Theisinger. But he added that there could be schedule conflicts for engineers who have to work on Opportunity’s landing and preparation for egress onto the Martian soil while simultaneously dealing with Spirit’s problem, if it still persists.

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