The Mars rover Spirit is still alive and is slowly recharging its batteries after a weekend dust storm that caused the craft鈥檚 power levels to drop to an all-time low.
Rover team members were awaiting a sign this week that the craft had survived the storm, which blanketed Spirit鈥檚 solar panels with dust.
During the storm, the amount of energy available to the craft dropped to an unsustainable 89 watt-hours, the lowest level seen since Spirit and its twin, Opportunity, landed on Mars with about 10 times that amount in January 2004.
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On Tuesday, the team commanded Spirit to shut down all unnecessary heaters on the craft, which was supposed to wake up once a day to survey the transparency of the atmosphere. To conserve its energy, the rover was ordered to wait until Thursday to communicate with the Mars Odyssey spacecraft as it passed by overhead.
But no one was sure if the commands took, or if the craft had entered a 鈥榣ow-power fault mode.鈥� That would have shut down the rover鈥檚 heaters in order to funnel as much energy as possible to the batteries, says Mars Exploration Rover project manager John Callas of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California.
Without the heaters, the rover would have been in a race to charge its batteries before they, and the rover鈥檚 electronics, were damaged by the extreme cold, he says.
鈥淓ither the rover was doing exactly what we told it to do, or it was going to be really bad news,鈥� Callas told 快猫短视频.
Slow charge
But Spirit beamed back telemetry on Thursday as scheduled, showing still-dusty skies but higher power levels 鈥� the rover collected 161 watt-hours of energy on the Martian day ending Thursday.
That energy level is not as high as it was before the storm, when the craft gathered some 240 watt-hours of energy per day. But Spirit is now collecting enough solar power to replenish its batteries.
鈥淲e鈥檙e above the break-even level,鈥� says rover project scientist Bruce Banerdt of JPL. 鈥淲e鈥檙e not draining the batteries. We鈥檙e actually slowing charging them, as long as we don鈥檛 tell them to do very much.鈥�
On Friday, Spirit was commanded to spend another four days in a low-power mode before attempting to communicate again.
The storm that hit Spirit came less than two weeks after similar weather in the far north sent NASA鈥檚 Phoenix lander to an early grave.
Dust devils
Spirit is parked on the sloping edge of a plateau called Home Plate in order to collect more sunlight. The rover鈥檚 solar panels are now tilted by about 22掳 northward, close to the optimal 20掳 needed to maximise sunlight collection during a two-week interruption in communications from 29 November to 15 December, when the Sun will lie between Mars and the Earth.
The storm has passed, but it is not clear how much more dust will settle onto the rover鈥檚 solar panels, further reducing its available power. Dust on the craft鈥檚 solar panels has cut their capacity to 30%, down from 33% before the storm.
The panels could be cleared by winds, possibly associated with dust devils, as they have been in years past. 鈥淪ome of our most effective cleaning events have occurred during dust-storm activity,鈥� Banerdt told 快猫短视频. 鈥淲e鈥檙e watching to see whether we catch a break.鈥�
Spirit was set to begin moving again after Christmas to its next targets: a hill and small crater some 200 to 300 metres away. But if the new dust on its panels does not clear, the craft may have to remain at its present location for longer. The added dust could also reduce the period of time each day that the craft could move.
