Launch of Shuttle Mission STS-42. Shuttle Discovery leaves two vast plumes of smoke as it climbs away from Kennedy Space Center at the beginning of Mission STS-42. The slightly brownish smoke comes from the two Solid Rocket Boosters (SRBs) that help propel the Shuttle in the first two minutes of the flight. STS-42 was launched on 22 January 1992, carrying the first International Microgravity Laboratory (IML-1) in its cargo bay. The crew of seven spent eight days in space, returning on 30 January 1992.