CloudSat is a NASA Earth observation satellite, which was launched on a Delta II rocket on April 28, 2006. It uses radar to measure the altitude and properties of clouds, adding to information on the relationship between clouds and climate in order to help resolve questions about global warming. CloudSat flies in formation in the "A Train", with several other satellites: Aqua, Aura, CALIPSO and the French PARASOL. The mission was selected under NASA's Earth System Science Pathfinder program in 1999. Ball Aerospace & Technologies Corp. in Boulder, Colorado, designed and built the spacecraft. CloudSat's primary mission was scheduled to continue for 22 months in order to allow more than one seasonal cycle to be observed.