KENNEDY SPACE CENTER, FLA. -- A Pegasus XL Expendable Launch Vehicle is prepared for towing to the Multi-Purpose Payload Facility (MPPF) where it will undergo testing, verification, and three flight simulations prior to its scheduled launch. The vehicle, nestled beneath an Orbital Sciences L-1011 aircraft, arrived at the Cape Canaveral Air Force Station Skid Strip on Dec. 17. It is commissioned to carry NASA's Solar Radiation and Climate Experiment (SORCE) spacecraft into orbit in late January 2003. Built by Orbital Sciences Space Systems Group, SORCE will study and measure solar irradiance as a source of energy in the Earth's atmosphere with instruments built by the University of Colorado's Laboratory for Atmospheric and Space Physics (LASP). KSC-02pd2015