were allotted to retract the airbags and deploy the lander petals. Rover design The rovers are six-wheeled, solar-powered robots that stand high, wide and long. They weigh , of which is the wheel and suspension system. The main box-like chassis forms the Warm Electronics Box (WEB). Drive system Each rover has six aluminium wheels mounted on a rocker-bogie suspension system, similar to that on Sojourner, that ensures wheels remain on the ground while driving over rough terrain. The design reduces the range of motion of the rover body by half, and allows the rover to go over obstacles or through holes (depressions) that are more than a wheel diameter () in size. The rover wheels are designed with integral compliant flexures which provide shock absorption during movement. Additionally, the wheels have cleats which provide grip for climbing in soft sand and scrambling over rocks. Each wheel has its own drive motor. The two front and two rear wheels each have individual steering motors. This allows the vehicle to turn in place, a full revolution, and to swerve and curve, making arcing turns. The motors for the rovers have been designed by the Swiss company Maxon Motor. The rover is designed to withstand a tilt of 45 degrees in any direction without overturning. However, the rover is programmed through its "fault protection limits" in its hazard avoidance software to avoid exceeding tilts of 30 degrees. Each rover can spin one of its front wheels in place to grind deep into the terrain. It is to remain motionless while the digging wheel is spinning. The rovers have a top speed on flat hard ground of 50 mm/s (2 in/s). The average speed is 10 mm/s, because its hazard avoidance software causes it to stop every 10 seconds for 20 seconds to observe and understand the terrain into which it has driven. Power and electronic systems When fully illuminated, the rover triplejunction solar arrays generate about 140 watts for up to four hours per Martian day (sol). The rover needs about 100 watts to drive. Its power system includes two rechargeable lithium ion batteries weighing each, that provide energy when the sun is not shining, especially at night. Over time, the batteries will degrade and will not be able to recharge to full capacity. For comparison, the Mars Science Laboratory's power system is composed of a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) produced by