Workers in the Vehicle Assembly Building oversee the replacement of Main Engine No. 1 in Space Shuttle Atlantis overhead.

Workers in the Vehicle Assembly Building oversee the replacement of Main Engine No. 1 in Space Shuttle Atlantis (overhead). An inventory review concerning defective main engine fuel pump tip seals indicated that defective seals might be present on the previous fuel pump for the engine. The decision was made to replace the suspect engine with one originally slated for Discovery. The main engine nozzle, visible in the photo, is 7.8 feet across and 9.4 feet high. Space Shuttle Atlantis is scheduled to launch no earlier than April 17, 2000, on mission STS-101 to resupply the International Space Station for the arrival of the next pressurized module, the Russian-built Zvezda