One of the six wheels on the Mars rover Spirit has stopped working and the solar-powered robot must propel itself up a slope to catch enough sunshine to keep operating, NASA said Friday.
The right front wheel previously had an episode of balkiness but this week the motor that turns the wheel stopped working, the space agency's Jet Propulsion Laboratory said in a statement.
"It is not drawing any current at all," said Jacob Matijevic, rover engineering team chief.
Engineers were considering whether the electrical motor's brushes — contacts that deliver power to the rotating part of the motor — have lost contact.
Spirit is trying to reach a position where it can get as much sunlight as possible during winter. But while the point of minimum sunshine is more than 100 days away, there already is only enough to power about one hour of driving on flat ground per day, JPL said.
The rover was 390 feet from a spot on the north-facing side of a feature called McCool Hill on Friday, where it could spend the southern-hemisphere winter with its solar panels angled toward the sun, JPL said.
Frequent stops to check whether the right front wheel had caught on anything slowed progress.
The solar panels have been producing 15 percent less electricity since February and are at less than half of their output during summer. JPL said Spirit would make about 40 feet a day under the current conditions.
Spirit's new wheel problem occurred this week during the rover's 779th Martian day.
Spirit and its twin, Opportunity, landed on opposite sides of the Red Planet in January 2004 and have long outlasted missions originally planned to last 90 Martian days.
Opportunity is closer to Mars' equator. The rover has finished a four-month study of a crater named Erebus and is making a 1.2-mile drive to the giant Victoria crater.