The Mars Rovers, Spirit and Opportunity, have certainly exceeded all expectations in terms of performance and are testimony to how much solar power technology has evolved.
The mission was originally meant to last only 3 months, but is now in its fifth year. Since landing on Mars, the rovers have sent over a quarter of a million images back to Earth and travelled over 21 kilometres.
When fully illuminated, the rovers solar panel arrays generate about 140 watts of power for up to four hours per sol (a Martian day). Each rover requires around 100 watts to drive. Its power system includes two rechargeable lithium ion batteries weighing just over 7kg each.
NASA expected capability of the solar arrays to generate power to be reduced to about 50 watts by the end of the original mission due to anticipated dust coverage on the solar arrays and seasonal changes; but 3 years into the mission, each rover’s power supplies were between 300 and 900 watt hours per day. The lithium ion batteries were also expected to degrade far more than they have.
It hasn’t all been smooth sailing. In July 2007, Martian dust storms were so intense, engineers feared that one or both of the rovers might be permanently disabled. However, the dust storms lifted and the panels were blown clean. These cleaning events have occurred more often than NASA predicted, keeping the arrays relatively free of dust and extending the life of the mission. The Mars rovers’ power systems have also had to contend with temperatures ranging from −40C to +40C.
Currently, atmospheric conditions have again deteriorated due to a large dust storm, with Spirit’s solar power production down to around 322 watt hours. It’s causing a concern for engineers, but is still far more power than the 240 watt hours being generated earlier in the year.
