3/21/91: NASA ISSUES MODIFICATIONS TO SHUTTLE MANIFEST RELEASE: 91-44 NASA managers today announced adjustments to modify the February 1991 Mixed Fleet Manifest. The modifications to the manifest were necessary after the STS-39 mission, scheduled for March with Space Shuttle Discovery, was postponed due to cracks on the orbiter's external tank door drive mechanism housing The flights now projected for calendar year 1991 begin with Space Shuttle Atlantis and the Gamma Ray Observatory flying in April. Following repairs to the door drive mechanism housing, Discovery will fly the STS-39 mission in May. The projected date for STS-40/Spacelab Life Sciences mission aboard Shuttle Columbia remains in May. Columbia will be taken off line as planned for structural inspections and modifications for Extended Duration Orbiter capability following completion of the STS-40 mission. The Tracking Data Relay Satellite mission originally scheduled to fly on Discovery in July is now on Atlantis in August. The Defense Support Program mission remains on Atlantis but will move from August to December. These two adjustments preserve the agency's capability to fly Discovery with the Upper Atmosphere Research Satellite payload during its required science window with launch projected now for October. The International Microgravity Laboratory mission which was planned for December 1991 will become the first flight in calendar year 1992. The mixed cargo flight of the Tethered Satellite System and the European Space Agency's European Retrievable Carrier originally scheduled for February on Shuttle Discovery will move to August 1992 and will fly on Space Shuttle Atlantis. Flights in the mid-1992 time frame remain in their original manifested positions with Atlas-1 in April, the Intelsat reboost mission in May which will involve the first flight of Space Shuttle Endeavour and the U.S. Microgravity Laboratory in June. Spacelab-J and the mixed cargo flight of the U.S. Microgravity Payload and the Laser Geodynamics Satellite also remain as scheduled for September 1992. The Canadian Experiments payload also is joining this mission. Adjustments to the manifest beyond September 1992 are still being examined and will be announced at a later date. 1991 Shuttle Launches DATE MISSION VEHICLE PAYLOAD April 1991 STS-37 Atlantis GRO May 1991 STS-39 Discovery AFP-675/IBSS May 1991 STS-40 Columbia SLS-1 August 1991 STS-43 Atlantis TDRS-E October 1991 STS-48 Discovery UARS December 1991 STS-44 Atlantis DSP 1992 Shuttle Launches DATE MISSION VEHICLE PAYLOAD February 1992 STS-42 Discovery IML-1 April 1992 STS-45 Atlantis ATLAS-1 May 1992 STS-49 Endeavour INTELSAT-R June 1992 STS-50 Columbia USML-1 August 1992 STS-46 Atlantis TSS-1/EURECA Sept. 1992 STS-47 Endeavour Spacelab-J Sept. 1992 STS-52 Columbia USMP/LAGEOS/CANEX