More than $3 million a day: That’s how much NASA is paying to have the Spirit and Opportunity rovers on Mars, calculated simply by dividing the $835 million budget for the rovers’ mission by the projected 240 days of operation. Of course, Spirit and Opportunity don’t get a dime of those millions: Instead, the money goes to the people who put the rovers on Mars, keep them going and harvest the precious scientific return from millions of miles away.