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More power for the ISS
By Matthias Gründer
Once again, problems on board the ISS demonstrated that spaceflight without humans is not feasible. The planned (and unplanned) installation and repair work in orbit could not have been carried out at all without the cosmic technicians, especially as there are no suitable robots.
The launch of this shuttle mission was marked by only one postponement. Delays have become virtually normal, given all the problems that have occurred in the past on the ageing shuttles. Yet the technicians were able to lean back satisfied, as it was only poor weather conditions at the Cape which had caused the delay. On the other hand, Discovery was in top form, which is why this was the shuttle entrusted with the first launch since the Columbia catastrophe. It lifted off at 19.47h local time on 9 December 2006, with five men and two women on board, among them Swedish ESA astronaut Christer Fuglesang and mission specialist Sunita Williams, who was due to relieve Thomas Reiter, the flight engineer of the 14th resident crew.
The cargo bay was packed with equipment: from front to back, the docking unit, a pallet containing equipment, tools, protective shields for the Zvezda module and three microsatellites due to be released shortly before the conclusion of the mission, plus the Spacehab logistics module in single configuration. Thanks to Spacehab, it was possible to more than double the stowage space on the orbiter. Almost three tonnes of cargo were contained in it, including provisions, drinking water, new clothing, tools, spare parts, a television camera etc.
The flight programme for this crew and their visitors was packed with activities. Scarcely had they attained orbit than the onboard computers were powered up and the cargo hatches opened, as these are fitted on the inside with large radiators to dissipate the heat from the interior of the orbiter. The now routine investigation of the underside of Discovery was also conducted with the aid of the new robotic arm, but the astronauts did not find any damage. Finally they installed a camera and extended the outer ring of the docking unit so that no further obstacles lay in the way to docking on the morning of 12 December.
After the welcome formalities, Sunita Williams was officially declared a member of the 14th, and at the same time a “herald” for the forthcoming 15th, resident crew, while Thomas Reiter was assigned to the Discovery team. On the same evening, Robert Curbeam and Christer Fuglesang withdrew to the “campout” in the Quest docking module under reduced air pressure to prepare themselves for their first spacewalk or “extravehicular activity“ (EVA) the next day. This began in the early afternoon. The primary aim was to connect the P5 spacer truss segment to the outermost left end of the truss (viewed facing the direction of flight), during which task mission specialist Joan Higginbotham performed all the work on the station crane arm. Once the assembly work was complete, the two spacewalkers secured all the electrical connections and replaced a faulty television camera. After six hours and 36 minutes, the ISS had put on another two tonnes in weight.
Something jams after six years' operating time in space
This was to be followed by further complicated work, namely the retraction of the upper left solar wing of segment P6 (once again viewed in the direction of flight) and recabling of all the power supply systems during a further EVA. Only then would it become possible to rotate the extended solar arrays mounted on segment P4 during the previous shuttle flight STS-115 towards the sun, thus enabling the ISS to be switched over to its permanent power system. At the same time, despite all this, the minimum power supply required to maintain work on board had to be safeguarded, as the other crew members meanwhile had a lot of work to do with unloading the Spacehab.
Unfortunately, it was not possible to entirely retract the left solar wing, which had been fitted to the ISS six years earlier. Meanwhile the partial retraction which had been achieved was at least sufficient to remove the obstruction to rotation of the new wing, and without further ado an extra EVA was fixed to complete the work.
The second job assigned to Curbeam and Fuglesang, the recabling work on 14 December, went according to plan, in fact it was accomplished in less time than had been allowed due to effective use of the time. After only five hours everything had been done, two of the four energy channels were supplying power to the station, while several hundred litres of freshly delivered ammonia were flowing through the station's cooling system. Towards the end of the week, Mission Control Houston agreed with the two onboard commanders that the shuttle landing would be delayed by one day to 22 December so that one extra EVA could be conducted on the 18th to eliminate the problems.
On 16 December, Curbeam and Sunita Williams climbed out of the station as planned and completed the cabling work on all the power generators. Then on the 18th Curbeam and Fuglesang finally managed to retract the jammed solar array manually, using their physical strength. The reason why automatic retraction had not completed turned out to be a tension cable which had sprung out of its mounting. The experience of this mission will be useful to the next group of astronauts when the second half of segment P6 is retracted in March. Meanwhile Curbeam attained a new record as a result of this extra, unplanned EVA, being the first astronaut to have undertaken four spacewalks during a shuttle mission.
From FLUG REVUE 2/2007
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