STS-35

STS-35 was the tenth flight of Space Shuttle Columbia, the 38th shuttle flight, and a mission devoted to astronomical observations with ASTRO-1, a Spacelab observatory consisting of four telescopes. The mission launched from Kennedy Space Center in Florida on 2 December 1990.

Crew notes
Prior to the Challenger disaster, this mission was slated to launch in March 1986 as STS-61-E. Jon McBride was originally assigned to command this mission, which would have been his second spaceflight. He chose to retire from NASA in May 1989 and was replaced as mission commander by Vance Brand. In addition, Richard N. Richards (as pilot) and David Leestma (as mission specialist), were replaced by Guy Gardner and Mike Lounge respectively. 59-year-old Brand was the oldest astronaut to fly into space until Story Musgrave, 61 on STS-80 in 1996, and U.S. Senator John Glenn, 77 when he flew on STS-95 in 1998.

Preparations and launch
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.

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 was leakage 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.

Mission highlights
The primary payload of mission STS-35 was ASTRO-1, the fifth flight of the Spacelab system and the second with the Igloo and pallet train configuration. The primary objectives were round-the-clock observations of the celestial sphere in ultraviolet and X-ray spectral wavelengths with the ASTRO-1 observatory, consisting of four telescopes: Hopkins Ultraviolet Telescope (HUT); Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE); Ultraviolet Imaging Telescope (UIT), mounted on the Instrument Pointing System (IPS). The Instrument Pointing System consisted of a three-axis gimbal system mounted on a gimbal support structure connected to a Spacelab pallet at one end and the aft end of the payload at the other, a payload clamping system for support of the mounted experiment during launch and landing, and a control system based on the inertial reference of a three-axis gyro package and operated by a gimbal-mounted microcomputer. The Broad-Band X-Ray Telescope (BBXRT) and its Two-Axis Pointing System (TAPS) rounded out the instrument complement in the aft payload bay.

The crew split into shifts after reaching orbit, with Gardner, Parker, and Parise comprising the Red Team; the Blue team consisted of Hoffman, Durrance, and Lounge. Commander Vance Brand was unassigned to either team and helped coordinate mission activities. The telescopes were powered up and raised from their stowed position by the Red Team 11 hours into the flight. Observations began under the Blue Team 16 hours into the mission after the instruments were checked out. In a typical ASTRO-1 ultraviolet observation, the flight crew member on duty maneuvered the Shuttle to point the cargo bay in the general direction of the astronomical object to be observed. The mission specialist commanded the pointing system to aim the telescopes toward the target. They also locked on to guide stars to help the pointing system remain stable despite orbiter thruster firings. The payload specialist set up each instrument for the upcoming observation, identified the celestial target on the guide television, and provided the necessary pointing corrections for placing the object precisely in the telescope's field of view. He then started the instrument observation sequences and monitored the data being recorded. Because the many observations created a heavy workload, the payload and mission specialists worked together to perform these complicated operations and evaluate the quality of observations. Each observation took between 10 minutes to a little over an hour.

Issues with the pointing precision of the IPS and the sequential overheating failures of both data display units (used for pointing telescopes and operating experiments) during the mission impacted crew-aiming procedures and forced ground teams at Marshall Space Flight Center (MSFC) to aim the telescopes with fine-tuning by the flight crew. BBXRT was directed from the outset by ground-based operators at Goddard Space Flight Center and was not affected. The X-ray telescope required little attention from the crew. A crew member would turn on the BBXRT and the TAPS at the beginning of operations and then turn them off when the operations concluded. After the telescope was activated, researchers at Goddard could "talk" to the telescope via computer. Before science operations began, stored commands were loaded into the BBXRT computer system. Then, when the astronauts positioned the Shuttle in the general direction of the source, the TAPS automatically pointed the BBXRT at the object. Since the Shuttle could be oriented in only one direction at a time, X-ray observations had to be coordinated carefully with ultraviolet observations. Despite the pointing problems, the full suite of telescopes obtained 231 observations of 130 celestial objects over a combined span of 143 hours. Science teams at MSFC and Goddard estimated that 70% of the mission objectives were completed. ASTRO-1 was the first shuttle mission controlled in part from the Spacelab Mission Operations Control facility at MSFC in Huntsville, Alabama.

During the flight, the crew experienced trouble dumping waste water due to a blocked waste water line, but managed to compensate using spare containers. Problems also affected one RCC thruster and an onboard text and graphics teleprinter used for receiving flight plan updates.

Additional payloads and experiments
Conducting short-wave radio transmissions between ground-based amateur radio operators and a Shuttle-based amateur radio operator was the basis for the Shuttle Amateur Radio Experiment (SAREX)-II. SAREX communicated with amateur stations in line-of-sight of the orbiter in one of four transmission modes: voice, slow scan television (SSTV), data or (uplink only) fast scan television (FSTV). The voice mode was operated in the attended mode while SSTV, data or FSTV could be operated in either attended or unattended modes. During the mission, SAREX was operated by Payload Specialist Ron Parise, a licensed operator (WA4SIR), during periods when he was not scheduled for orbiter or other payload activities. A ground-based experiment to calibrate electro-optical sensors at Air Force Maui Optical Site (AMOS) in Hawaii was also conducted during the mission. The Space Classroom Program: Assignment: The Stars project was carried out to spark student interest in science, mathematics and technology. Mission Specialist Hoffman conducted the first classroom lesson taught from space on 7 December in support of this objective, covering material on the electromagnetic spectrum and the ASTRO-1 observatory. A supporting lesson was taught from the ASTRO-1 control center in Huntsville.

Landing
The mission was cut short by one day due to impending bad weather at the primary landing site, Edwards Air Force Base, California. The Orbital Maneuvering System (OMS) engines were fired at 8:48 PM PST over the Indian Ocean to deorbit the spacecraft, which landed on Runway 22 at Edwards Air Force Base, CA at 9:54 PM, 10 December 1990 after a mission duration of 8 days, 23 hours, and 5 minutes. This was the fourth night landing of the shuttle program. Rollout Distance: 10,447 feet (3.184 km). Rollout Time: 58 seconds. Columbia returned to KSC on 20 December on the Shuttle Carrier Aircraft. Landing Weight: 102208 kg.