Two Space Shuttle missions—the STS-51-L and the STS-61-E—had been scheduled to observe Halley's Comet from low Earth orbit. The STS-51-L mission carried the Shuttle-Pointed Tool for Astronomy (SPARTAN-203) satellite, also called the Halley's Comet Experiment Deployable (HCED). The ill-fated mission was ended by the "Challenger" disaster. Scheduled for March 1986, STS-61-E was a "Columbia" mission carrying the ASTRO-1 platform to study the comet. Owing to the suspension of the American human spaceflight program after the "Challenger" explosion, the mission was canceled and ASTRO-1 would not fly until late 1990 on STS-35.