The second Mars Exploration Rover (MER-1) arrives at the Payload Hazardous Servicing Facility. MER-2 and other hardware have already arrived at KSC for processing. While at KSC, each of the rovers, their aeroshells and landers will undergo a full mission simulation. After spin balance testing, each spacecraft will be mated to a solid propellant upper stage booster that will propel the spacecraft out of Earth orbit. Approximately 10 days before launch they will be transported to the launch pad for mating with their respective Boeing Delta II rockets. The rovers will serve as robotic geologists to seek answers about the evolution of Mars, particularly for a history of water. The rovers are identical to each other, and will land at different regions of Mars. Launch of the MER-1 is scheduled for May 30. MER-2 will follow June 25.