View of three main engines in preparation for STS-51

S93-43619 (18 Aug 1993) --- At Launch Pad 39B, work is under way to remove and replace the three main engines on the Space Shuttle Discovery. Here, Rocketdyne workers Jim Tibble (left), John Mooney and Ken Bair are assisting with the removal of the first engine, main engine no. 1, using the engine vertical installer. A failed sensor in main engine no. 2 led to the shutdown of all three engines three seconds before liftoff of mission STS-51 on August 12, 1993. Because it is difficult to perform the necessary inspections, refurbishment, and retesting of a fired engine on a vehicle at the pad, NASA opted to install a fresh set of engines on Discovery.