Workers in the Payload Hazardous Servicing Facility check over the newly arrived second Mars Exploration Rover, MER-1. It will undergo prelaunch testing, including deployment of the lander petals, the rover's solar arrays, camera mast and camera. 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.