The Space Division began the development of the Military Strategic and Tactical Relay (Milstar) communications satellite constellation in 1982, which was designed specifically to support the National Command Authority. The 1986 Challenger disaster illustrated some of the major dangers of using the Space Shuttle as the sole space launch system. The Development of the Titan IV space launch vehicle began in 1985 but gained new importance after the disaster. Development also started on the Delta II and Atlas II space launch vehicles, both derived from earlier ballistic missiles.