STS-74 - Mission Background

Mission Background

The crew's preparation for the mission had begun some thirteen months earlier in 1994, with the crew being trained in the operation of the space shuttle, the mating and docking procedures that would be required as Atlantis approached Mir later in the mission, and the management of the various scientific experiments being carried on the orbiter during the mission.

Preparation of Atlantis itself for mission STS-74 began with the replacement of three thrusters in Atlantis's right-hand Orbital Maneuvering System pod in bay 2 of the Orbiter Processing Facility on 25 August 1995. Installation of the three Space Shuttle Main Engines (SSMEs) on Atlantis was completed on 5 September 1995, as were closeout operations on the Russian docking module.

On 7 November, engineers determined that there was no additional work needed to verify the solid rocket boosters for flight, following discovery of small cracks in the hold-down posts attached to boosters that had flown earlier that year. Close inspections of the STS-74 stack determined that no such cracks were present on the boosters to be used for the mission.

Pad 39A was cleared on 9 November in preparation for loading of the onboard cryogenic tanks with the cryogenic oxygen and hydrogen reactants that provided electricity through the three onboard fuel cells, and water for the flight as a by-product.

The initial launch attempt, scheduled for 11 November 1995 at 7:56 am EST (12:56 pm UTC) was postponed due to poor weather at the Transatlantic Abort (TAL) site. The original launch window was 6 min 57 secs and the countdown had begun on schedule. The crew was on board when the postponement was called at the T-minus 5 minute mark at approximately 7:51 am EST (12:51 pm UTC).