A year and a half after twin robot rovers thrilled space fans with their hijinks on Mars, NASA is heading there again. But Tuesday, the agency announced Wednesday’s scheduled blast off was postponed one day so that equipment used to guide the vehicle during liftoff can be checked out by the manufacturer. The fourth Mars orbiter is set to launch on an Atlas V rocket Thursday from Cape Canaveral, Florida. It will carry some of the most sophisticated science instruments ever sent into space, including the largest telescopic camera sent to another planet.