NASA gave the go-ahead for both Mars Exploration Rovers — Spirit and Opportunity — to keep on rolling. Each robot has been handed up to five months of overtime assignments after completing their individual three-month prime mission. “Even though the extended mission is approved to September, and the rovers could last even longer, they also might stop in their tracks next week or next month,” said Firouz Naderi, Manager of Mars Exploration at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, where the rovers were built and are controlled.