By the early summer of 1991, Columbia was well on the way to flying another scientific mission, STS-40 - although this time, it would have a very different flavour: dedicated entirely to medical research. NASA already had plans to send the flagship of the Shuttle fleet back to Palmdale later in 1991 to begin a lengthy series of modifications that would enable her to fly longer missions of up to 16 days. That could only take place, however, after the satisfactory completion of the STS-40 mission which, like ASTRO-1, had been waiting many years for its chance to fly.
Unlike the pallet-train-and-igloo combination flown on STS-35, Columbia would this time be transporting the bus-sized Spacelab module into orbit for the first Spacelab Life Sciences mission, known as 'SLS-1'. It would be the first time either of the two ESA-built pressurised modules had been used since the Challenger disaster, only its fourth outing overall and the second time it had been carried on board Columbia. Originally, in pre-Challenger days, the mission had been known as Spacelab-4 and, like ASTRO-1, its four-person science crew had remained attached to it for many years.
Although, as Steve Hawley has said, pre-Challenger crews changed quite frequently, one general point that has remained consistent throughout the Shuttle programme is that Spacelab science crews do remain intact and attached to 'their' payload. Therefore, it was always clear to Mission Specialists Jim Bagian and Rhea Seddon and Payload Specialists Drew Gaffney and Bob Phillips that they could confidently train for the mission, reasonably safe in the knowledge that they would one day fly it. Unfortunately, for one of them at least, that would not be the case.
Phillips, the oldest of the four, was removed from the crew in mid-1989 after being medically disqualified. His replacement was biochemist Millie Hughes-Fulford who, like Gaffney, would be making her first trip into space. Bagian and Seddon, on the other hand, each had completed one previous mission: the former flew on STS-29, which launched an important communications satellite for NASA in March 1989, while the latter had been on STS-51D in April 1985, which featured an unplanned spacewalk to attempt to overcome a problem with the newly released Leasat-3 satellite. Interestingly, Seddon was also married to fellow astronaut Hoot Gibson.
Following a similar pattern to that blazed by STS-35, the crew also had a three-member team who would be responsible for monitoring Columbia's systems and keeping the spacecraft in generally good shape while their counterparts handled the bulk of the medical experiments in the Spacelab module. The Commander for STS-40 was Bryan O'Connor, who had flown once before, in November 1985; his Pilot, Sid Gutierrez, and the third Mission Specialist - and 'flight engineer' - Tammy Jernigan, on the other hand, were both first-timers.
Gutierrez was a late addition to the crew; the original Pilot was John Blaha, but he moved onto STS-33 to replace the Pilot of that mission, who had tragically died in an air crash. However, Blaha's ties with Spacelab Life Sciences were not to be severed and he later commanded the second SLS flight late in 1993. Jernigan became, at just a few weeks past her thirty-second birthday when STS-40 lifted off, one of the youngest women to fly in space. The presence of three women on the crew - Seddon, Hughes-Fulford and Jernigan - set yet another record.
When O'Connor, Gutierrez and Jernigan began their training in earnest in the summer of 1989, they confidently expected to launch the following June, but a multitude of delays caused by hydrogen leaks which affected two of NASA's three Shuttles pushed the mission into the autumn of 1990 and eventually well into the next summer. After Columbia returned from the long-delayed STS-35 mission, she was ensconced in the OPF where the ASTRO-1 and the BBXRT payloads were removed and electrical and mechanical provisions made to install the Spacelab module and its support equipment.
By the end of March 1991, the module was in Columbia's payload bay and on 3 April the tunnel was installed to connect it to the middeck airlock hatch. Meanwhile, problems arose with the preparation of STS-40's SRBs: after stacking, a set of gauges affixed to the boosters' aft skirts (their lowermost segments) started giving anomalous 'load' readings. Engineers suspected that their hold-down posts were misaligned and a decision was made to destack, and then restack, them. By mid-April, the boosters were complete, the External Tank was attached and Columbia arrived in the VAB before the end of that month.
After a smooth rollout to Pad 39B on 2 May, the complete seven-member crew arrived in Florida for their Terminal Countdown Demonstration Test (TCDT); while they were performing it, the previous Shuttle crew - that of STS-39 - returned home to KSC after an eight-day Department of Defense mission. Following a now-customary emergency escape exercise, the STS-40 astronauts returned to Houston to complete the final stages of their training. It would not be long before they were back for what they hoped would be the real thing.
On 19 May, O'Connor led his crew into Florida in a fleet of four T-38s and alighted on the SLF runway to greet the waiting journalists. ''We're all ready to go. Light 'em,'' said Jernigan excitedly. Behind her in the distance, standing majestically on the pad, was Columbia, just three days away from her scheduled 22 May launch. ''We hope you all have your fingers crossed for clear skies and smooth sailing,'' added Seddon. Weather forecasters were anticipating a 90% chance of favourable weather and Test Director Mike Leinbach was reporting a smooth countdown so far.
He spoke too soon. By 20 May, NASA managers opted to postpone the launch when a leaking liquid hydrogen transducer in the Shuttle's aft compartment - which had been removed and replaced during the exhaustive leak tests in the summer of 1990 - failed an analysis by its vendor and revealed weld defects. This increased fears that, if a weld failed during Columbia's ascent, one or more of the nine liquid hydrogen and oxygen transducers projecting into the fuel and oxidiser lines could crack, break off and be ingested by the main engines' turbopumps.
''I'm discouraged that it happened so late prior to our launch,'' said O'Connor. ''But, on the other hand, they are talking about a potentially very serious problem, and the last thing we want to do is launch with a very serious problem on board. The temperature probes just upstream of the turbopumps for those engines have to be in good shape.'' Indeed, the possibility of disaster had the defects gone undetected does not bear thinking about for, almost certainly, the engines would have failed or even exploded if a transducer had broken away and lodged inside one of them.
Moreover, one of Columbia's five GPCs - the Number 4 unit, part of the 'redundant' set - failed, as did an MDM, which controlled her hydraulic ordnance and the functions of her aft-mounted RCS and OMS thrusters. A new GPC and MDM were fitted and one liquid hydrogen and three liquid oxygen transducers were replaced. Launch was provisionally booked for 1:00 pm on Saturday 1 June but this attempt was also postponed at the T —20 minute mark after several unsuccessful efforts to calibrate one of Columbia's IMUs.
Over the weekend, the unit was replaced and tested and the countdown clock again began ticking down, this time towards a projected launch at 12:00 midday on 5 June. With no mechanical obstacles in their way, the crew made their final preparations to go. One of these was the insertion of a catheter in Drew Gaffney's arm to monitor cardiovascular changes and fluid shifts in his body during Columbia's ascent and first few hours in orbit. The clock was held for almost an hour and a half when the weather did not cooperate, but STS-40 set off at 1:24:51 pm.
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