All went well until the beginning of February. The myriad of experiments arrived in Florida in July 1992 and the laborious process of installing them into the pressurised module began in September. After a slight delay caused by problems latching Columbia's payload bay doors, the 11,340-kg Spacelab-D2 cargo - including its experiment-laden USS pallet - was loaded on board the Shuttle on 11 January 1993 and checks confirmed their electrical and mechanical compatibility. After being transferred to the VAB for attachment to her boosters and tank, the complete stack was rolled out to Pad 39A on 7 February.
The mission's problems really began when Columbia was at the pad. Concerns had been raised since late January that her three main engines might have contained obsolete versions of tip-seal retainers on the blades of their high-pressure liquid oxygen turbopumps. These seals minimised the flow of gas around the tips of the turbine blades and, in doing so, enhanced the turbopumps' performance. Each seal was held in place by its own 'retainer'. The uncertainty was that NASA could not conclusively determine from the STS-55 pre-flight processing paperwork whether the retainers were of the 'old' or 'new' variety.
If they were of the old type, they needed to be checked before each mission; if of the newer type, on the other hand, they could fly several times without inspection. To play things safe, Columbia's main engines were removed, inspected and their retainers checked - they were of the newer-specification type. By the time this work had been finished and the engines were back in place, it was the end of February and NASA was forced to reschedule the STS-55 launch for ''no earlier than'' 14 March.
Despite ridicule heaped on the episode by the media, John Plowdon - the KSC division manager of engine-builder Rocketdyne - stood by the decision to postpone the launch and check the retainers on safety grounds. ''We're still confident that was the right decision to make,'' he told journalists. To accommodate the almost-three-week delay, the film on one USS-mounted astronomical instrument - the Galactic Ultra-wide-angle Schmidt System (GAUSS) - had to be changed and two other Spacelab experiments needed to have their batteries replaced. However, more trouble was afoot.
On 2 March, during a flight readiness test, a 33-cm flex hose in Columbia's aft compartment - which served as part of the hydraulic system to move the main engines, elevons and speed brake - burst and spilt several litres of hydraulic fluid. Although the hose itself was capped within a few seconds of the incident, it was decided to remove and check all 12 hydraulic hoses. Nine were examined and reinstalled and three new ones were fitted. By 9 March the task was complete and Shuttle director Tom Utsman had nothing but praise for the tremendous work done by his team.
''The team has done a great job in addressing and closing issues such as the hydraulic flex hose problem and putting together a new plan for processing activities,'' he said. He also paid tribute to the US Navy, US Air Force and Hughes Space and Communications Company, who had agreed to postpone the launch of an Atlas rocket carrying a military communications satellite in order to give Columbia another shot in the third week of March. As with all rockets launched from Florida, the ascent trajectories of Shuttle missions are closely monitored and tracked by Eastern Test Range antennas.
Only one rocket can be launched on any one day, thus enabling the range to concentrate its full resources on that mission. The agreement of General Dynamics, who built the Atlas, to offer their 'slot' on 21 March to Columbia provided a much-needed boost, particularly to the Germans, who were reportedly paying a million dollars every day just to keep their Spacelab-D2 experiments and ground personnel flight-ready. The mission, with its $560-million pricetag, had already been criticised and the enormous cost of reunification since the Berlin Wall was torn down in 1989 had imposed restrictions on Germany's space ambitions.
The country - or West Germany, at least - had been one of ESA's strongest members before reunification, but now had to commit an increasing share of its finances to extensive public works improvements in the former East Germany. ''We all realise the effort that needs to be spent to get [the former East Germany] up to speed, infrastructure-wise,'' said Spacelab-D2 Project Manager Hauke Dodeck. ''We have very tight budgets in all areas, including research and technology.'' Already, Spacelab-D3 had been cancelled, in favour of limited participation in a general, 'pan-European' Spacelab-E1 mission. Ultimately, that flight, too, never took place.
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