April 14, 2009
The team operating NASA's Mars Exploration Rover Spirit is examining data received from the spacecraft in recent days to diagnose why it apparently rebooted its computer at least twice April 11-12.
"While we don't have an explanation yet, we do know that Spirit's batteries are charged, the solar arrays are producing energy, and temperatures are well within allowable ranges," said John Callas, project manager for Spirit and Opportunity at NASA's Jet Propulsion Laboratory (JPL), Pasadena, California. "We have time to respond carefully and investigate this thoroughly. The rover is in a stable operations state called auto mode and taking care of itself. It could stay in this stable mode for some time, if necessary, while we diagnose the problem."
Spirit communicated with controllers Friday, Saturday, and Sunday, April 10-12, but some of the communication sessions were irregular. One of the computer resets apparently coincided in timing with operation of the rover's high-gain dish antenna.
The rover team has the advantage of multiple communication options. Spirit can communicate directly with Earth via either the pointable high-gain antenna or, at a slower data rate, through a low-gain antenna that does not move. Additionally, communications can be relayed by Mars orbiters, using the UHF (ultra-high frequency) transceiver, a separate radio system on the rover.
"To avoid potential problems using the pointable antenna, we might consider for the time being just communicating by UHF relay or using the low-gain antenna," Callas said.
Spirit finished its 3-month prime mission on Mars 5 years ago and has kept operating through multiple mission extensions.
The rover's onboard software has been updated several times to add new capabilities for the mission, most recently last month. The team is investigating whether the unexpected behavior in recent days could be related to the new software, but the same software is operating on Opportunity without incident.
"We are aware of the reality that we have an aging rover, and there may be age-related effects here," Callas said.
In the past 5 weeks, Spirit has made 390 feet (119 meters) of progress going counterclockwise around a low plateau called "Home Plate" to get from the place where it spent the past martian winter on the northern edge of Home Plate toward destinations of scientific interest south of the plateau. On March 10, after several attempts to get past obstacles at the northeastern corner of Home Plate, the rover team decided to switch from a clockwise route to the counterclockwise one. Subsequent events have included Spirit's longest 1-day drive since the rover lost use of one of its wheels 3 years ago, plus detailed inspection of light-toned soil exposed by the dragging of the inoperable wheel.
Meanwhile, halfway around Mars, Opportunity has continued progress on a long-term trek toward Endeavour Crater, a bowl 14 miles (23 kilometers) in diameter and still about 12 miles (19 kilometers) away. Last week, a beneficial wind removed some dust from Opportunity's solar array, resulting in an increase by about 40 percent in the amount of electrical output from the rover's solar panels.