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 Endeavour, then still under construction.
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.

Columbia was rolled out to Pad A for the second time 9 August to support a 1 September launch date.
Two days before launch, the avionics box on the BBXRT portion of the ASTRO-1 payload malfunctioned and had to be changed and retested.
Launch was rescheduled for 6 September.
During tanking, high concentrations of hydrogen were again detected in the orbiter's aft compartment, forcing another postponement.
NASA managers concluded that Columbia had experienced separate hydrogen leaks from the beginning: one of the umbilical assembly (now replaced) and one or more which had resurfaced in the aft compartment.
Suspicion focused on the package of three hydrogen recirculation pumps in the aft compartment.
These were replaced and retested.
A damaged Teflon cover seal in the main engine number three hydrogen prevalve was replaced.
Launch was rescheduled for 18 September.
The fuel leak in the aft compartment resurfaced during tanking, and the launch was scrubbed again.
The STS-35 mission was put on hold until problem resolved by a special tiger team assigned by the Space Shuttle director.

Columbia was transferred to Pad B on 8 October to make room for Atlantis on Mission STS-38.
Tropical storm Klaus forced another rollback to the VAB on 9 October.
The vehicle was transferred to Pad B again on 14 October.
Another mini-tanking test was conducted on 30 October, using special sensors and video cameras and employing a see-through Plexiglas aft compartment door.
No excessive hydrogen leakage was detected.
With the problem resolved, the flight had only to wait for the completion of STS-38, imparting another four-week delay.
A scheduled launch date of 30 November was moved by several days due to concerns that observations of astronomical targets would be adversely affected.
Liftoff on 2 December was delayed by 21 minutes to allow the Air Force time to observe low-level clouds that might impede the tracking of the Shuttle's ascent.
Liftoff finally occurred on 2 December 1990, 1:49:01AM EST, the ninth night launch in shuttle history and the second for Columbia.
A nominal ascent to orbit followed.
This was one of the most delayed launches of the space shuttle program.
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 Endeavour, then still under construction. 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.
Columbia was rolled out to Pad A for the second time 9 August to support a 1 September launch date. Two days before launch, the avionics box on the BBXRT portion of the ASTRO-1 payload malfunctioned and had to be changed and retested. Launch was rescheduled for 6 September. During tanking, high concentrations of hydrogen were again detected in the orbiter's aft compartment, forcing another postponement. NASA managers concluded that Columbia had experienced separate hydrogen leaks from the beginning: one of the umbilical assembly (now replaced) and one or more which had resurfaced in the aft compartment. Suspicion focused on the package of three hydrogen recirculation pumps in the aft compartment. These were replaced and retested. A damaged Teflon cover seal in the main engine number three hydrogen prevalve was replaced. Launch was rescheduled for 18 September. The fuel leak in the aft compartment resurfaced during tanking, and the launch was scrubbed again. The STS-35 mission was put on hold until problem resolved by a special tiger team assigned by the Space Shuttle director.
Columbia was transferred to Pad B on 8 October to make room for Atlantis on Mission STS-38. Tropical storm Klaus forced another rollback to the VAB on 9 October. The vehicle was transferred to Pad B again on 14 October. Another mini-tanking test was conducted on 30 October, using special sensors and video cameras and employing a see-through Plexiglas aft compartment door. No excessive hydrogen leakage was detected. With the problem resolved, the flight had only to wait for the completion of STS-38, imparting another four-week delay. A scheduled launch date of 30 November was moved by several days due to concerns that observations of astronomical targets would be adversely affected. Liftoff on 2 December was delayed by 21 minutes to allow the Air Force time to observe low-level clouds that might impede the tracking of the Shuttle's ascent. Liftoff finally occurred on 2 December 1990, 1:49:01AM EST, the ninth night launch in shuttle history and the second for Columbia. A nominal ascent to orbit followed. This was one of the most delayed launches of the space shuttle program.
STS-35