Mars Rover Spirit Surviving on a Low Energy Diet

Written by Ian O'Neill

Last week, Mars Exploration Rover Spirit looked as if its sols were numbered. Hot on the heals of the demise of the frozen Phoenix lander, Spirit was about to succumb to a low- energy death brought on by a dust storm. The build-up of dust on the rover's solar panels were already causing a serious problem, but as a storm raged over Gusev Crater, power output from the panels slumped to an all-time low. As Nancy reported on November 11th, mission controllers were forced to switch Spirit into a low-energy state, leaving them with no other choice but to command the robot to be silent. Although tensions were high, Spirit broke the silence last Thursday.

Now NASA controllers are working hard to manage Spirit's power production, hopefully extending the life of the highly successful rover longer still…

At its worst, Spirit's solar panels were outputting 89 watt hours of energy just before NASA mission control took decisive action by shutting down non-essential heaters on the rover. Before the storm, Spirit was already covered in a thick layer of dust from nearly five years of Mars roving, allowing only 33% of the sunlight falling on the panels to be used by the photovoltaic cells. During the storm, the dust situation had worsened, valuable sunlight was getting blocked by atmospheric dust clouds. Spirit was in trouble.

At their peak, both Spirit and Opportunity were able to generate 700 watt hours of energy. Should their power output drop to 150 watt hours, batteries start to drain while running heaters to keep essential equipment and instrumentation warmed. Spirit's 89 watt hours was therefore a dire situation. Fortunately after the intrepid rover rode out the storm and checked in with mission control, by the end of Thursday, NASA was pleased to see Spirit's solar panels generating 161 watt hours of energy. After four days, the skies were clearing and Spirit could begin slowly recharging its batteries. However, the layer of dust on top of the solar panels had thickened, allowing 3% less light to get through.

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