Solar panels on the cruise stage of a Mars Exploration Rover are seen as the element is rotated for processing.

Solar panels on the cruise stage of a Mars Exploration Rover are seen as the element is rotated for processing. Once functional testing and mission simulation of the flight elements is complete, the elements will be integrated for flight. There are two rovers, identical to each other, and each will land at different regions of Mars. They are designed to cover roughly 110 yards each Martian day over various terrain. Each rover will carry five scientific instruments that will allow it to search for evidence of liquid water that may have been present in the planet's past. The first rover has a launch window opening May 30, and the second rover a window opening June 25.