The mission of the flight that ended in disaster was named STS-51-L. It was the tenth mission for "Challenger". STS-51-L was scheduled to deploy the second in a series of Tracking and Data Relay Satellites, carry out the first flight of the "Shuttle Pointed Autonomous Research Tool for Astronomy" (SPARTAN-203) / Halley's Comet Experiment Deployable in order to observe Halley's Comet, and for civilian teacher Christa McAuliffe to carry out several lessons from space as part of the Teacher in Space Project and Shuttle Student Involvement Program (SSIP). One of the crew members of this mission, Gregory Jarvis, was originally scheduled to fly on the previous shuttle flight (STS-61-C). However, he was reassigned to this flight and replaced by Congressman Bill Nelson.