Spacelab A Multipurpose Research Facility

Towards the end of 1969, not long after Neil Armstrong and Buzz Aldrin became the first humans to set foot on the Moon, NASA outlined a number of key directions for the United States space programme after Apollo. President Kennedy's challenge to land a man on the lunar surface before the end of the decade had been met, but it was not until this time that serious consideration - and dollars - were given to what would be done next. Of course, Earth-orbital space stations, Moon bases and trips to Mars before the end of the century were envisioned but considered unlikely.

Establishing some kind of permanent, or at least frequent, human presence in space was of major importance to NASA. During the first eight years of sending people aloft, from Al Shepard's pioneering suborbital 'hop' to Apollo 11's triumphant landing at the Sea of Tranquillity, fewer than two dozen astronauts had gazed down on the Earth. Some of them, admittedly, had flown as many as three times, but two dozen of a United States population of a quarter of a billion was insignificant. If NASA was to maintain public interest, it had to make access to space routine.

A space station called Skylab was already being built, but the most important long-term aim was the development of the Shuttle, for which the United States sought foreign cooperation. Already, Canada had agreed to develop the Shuttle's RMS mechanical arm and, in December 1972, just as the final Apollo crew prepared to leave the Moon, the European Space Research Organisation (ESRO) agreed at a ministerial conference in Brussels to develop a modular space laboratory for the Shuttle, known as 'Spacelab'.

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ESRO, which in 1974 merged with the European Launcher Development Organisation (ELDO) to become today's European Space Agency (ESA), would design, develop and manufacture the Spacelab system for carriage in the Shuttle's payload bay, in return for flying its own astronauts into space on specific missions. In September 1973, the contracts with NASA were finally signed and the largest international cooperative venture in space so far was set in motion. Spacelab would be a multipurpose scientific research platform, capable of supporting some experiments in a pressurised, 'shirt-sleeve' environment and exposing others to the vacuum of space.

As has already been seen, the segment of Spacelab designed to expose experiments directly to the space environment was flight-tested during the STS-2 and STS-3 missions. Known as 'pallets', they were essentially U-shaped rigid metal frames measuring about 3 m long by 3.9 m wide and covered with aluminium panels onto which large telescopes, antennas or sensors requiring unobstructed large-fields-of-view could be attached. On STS-2, for example, a single engineering version of the pallet was used to carry a synthetic-aperture radar, as well as a number of other experiments.

Up to five pallets, bolted together to form a rigid 'train', can be flown on board a single Shuttle mission. The most pallets actually flown on one mission has been three - on board Spacelab-2 in July 1985 - and these versatile platforms continue to be used into the International Space Station era. On missions that employ only pallets, a 2.1-m-tall cylinder called an 'igloo' stands vertically at the forward end of the 'front' pallet. Igloos are temperature-controlled, pressurised containers which house subsystems and equipment needed to support the pallet-mounted instruments.

The second major component of Spacelab, originally called the 'sortie can' but later renamed the 'module', was a bus-sized aluminium cylinder in which experiments that needed hands-on attention from astronauts could be accommodated. It came in two sections: a 'core' module, which carried data-processing equipment, a workbench and a set of air-conditioned experiment racks lining its walls; and an 'experiment' module, which provided additional space for scientific activities in orbit. Although the core could be flown on its own, this configuration was never used, and all module flights employed both sections joined together.

With a pressurised volume of 75 m3, this so-called 'long module' - of which two flight units were built - flew 16 times between November 1983 and May 1998 and was used to carry experiments ranging from life sciences, to technology and fluid physics, to materials processing. Of those flights, 11 were on board Columbia. The version using only the core section, known as the 'short module', was due to have flown an Earth-observation mission in 1986, but the Challenger disaster ended that. Although the mission was flown under the new name of 'ATLAS-1' in March 1992, it was as a pallet-only configuration.

When one considers the dimensions of the short module, it is clear why NASA opted to use the longer version: the latter was 7.1 m long, almost double that of the former and thus virtually doubled the amount of 'rack space' in which to store experiments. These 'racks' were essentially refrigerator-sized facilities that could be loaded with experiments and 'rolled' into the module's cylindrical shell. The long module also offered a long central aisle of floor space, onto which additional experiments could be affixed, and provided two ceiling openings for a viewing window or scientific airlock.

''The racks were pretty much standard,'' remembered NASA's former director of space life sciences, Gene Rice. ''You either had a drawer in a rack or you had a whole rack, or you might have a double rack, depending on the magnitude or size of the experiment. We would help [experiment customers] through the process of designing their experiment, integrating it into a Spacelab rack, doing the testing that they needed to do [and] getting it to a [NASA] centre. They would have to show that they met the safety requirements to put it into the Spacelab and to fly it.''

The racks contained air ducts to cool experiments and power-switching panels. On the first 'dedicated' Spacelab mission, flown on Columbia on STS-9 in November 1983, the module contained 12 racks, of which the two nearest the entrance were devoted to control subsystems. The ceiling of the core section provided a 0.3-m-wide opening for a high-optical-quality Scientific Window Adaptor Assembly (SWAA), through which Earth-observation cameras could be aimed, and that of the experiment section provided a Scientific Airlock (SAL), into which samples requiring exposure to space could be easily inserted and later retrieved.

As with other payload bay-mounted hardware, the exterior of the modules and pallets were covered with a layer of passive thermal insulation material to protect them from extremes of sunlight or frigid orbital darkness. The module was situated in the midpoint of the bay, to avoid jeopardising the Shuttle's centre-of-gravity constraints during landing, and was linked to the crew cabin's airlock hatch by a 5.8-m-long tunnel. Also, because the Spacelab's hatch was 1.5 m 'higher' than the airlock hatch, a 'joggle' section was included in the tunnel to compensate for this vertical offset.

Of course, astronauts might still need to perform emergency space-walks, perhaps to close the payload bay doors if it became impossible to do this from the flight deck. With this in mind, a 'mini-airlock' was built into the tunnel and a pair of spacewalkers could essentially close off the tunnel without having to depressurise the crew cabin or the Spacelab. Although a spacewalk was never actually performed during a module flight, on one mission in June 1991 such action was briefly considered when a problem with some thermal insulation threatened to interfere with the closure of Columbia's payload bay doors.

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