Guy Gardner (astronaut)

The much-delayed ASTRO-1 had originally been manifested to fly on what would have been the next shuttle mission after Challenger's ill-fated STS-51L as STS-61E in March 1986. The mission was remanifested as STS-35 during the long stand-down after the accident with the addition of the Broad-Band X-Ray Telescope (BBXRT-01), and the original ASTRO-1 payload was brought out of storage and recertified for flight.Columbia rolled out to Pad 39A in late April 1990 for a scheduled launch date of 16 May. Following the Flight Readiness Review (FRR), announcement of a firm launch date was delayed to change a faulty freon coolant loop proportional valve in the orbiter's coolant system. At the subsequent Delta FRR, the date was set for 30 May. Launch on 30 May was scrubbed during tanking due to a minor hydrogen leak in the tail service mast on the mobile launcher platform and a major leak in the external tank/orbiter quick disconnect assembly. Hydrogen was also detected in the orbiter's aft compartment and believed to be associated with a leak involving the 17-inch umbilical assembly.

Leakage at the 17-inch umbilical was confirmed by a mini-tanking test on 6 June. The leakage could not be repaired at the pad, and the vehicle was rolled back to the Vehicle Assembly Building (VAB) 12 June, demated, and transferred to the Orbiter Processing Facility (OPF). The orbiter-side 17-inch umbilical assembly was replaced with one borrowed from the yet-to-arrive Shuttle Endeavour. The external tank was then fitted with new umbilical hardware. The ASTRO-1 payload was reserviced regularly and remained in Columbia’s cargo bay during orbiter repairs and reprocessing.