An Ambitious Venture

As already mentioned, ASTRO-1 marked the first time Columbia had carried the pallet-train-with-igloo combination and was also her first 'operational' Spacelab mission, following the inaugural test flight of the system on STS-9. It would also be the first operational mission of the Instrument Pointing System (IPS), which was attached to the Spacelab pallets and provided a base for the three telescopes. The IPS allowed the telescopes to be pointed with an accuracy of just two arc-seconds and could move them backwards and forwards, side-to-side and 'roll' them in a 22-degree circle about its 'straight-up' position.

It also featured a clamp to hold the telescopes horizontally in Columbia's payload bay during ascent and re-entry and its movements were commanded from the aft flight deck's control panel. For safety reasons, there was provision for the emergency jettisoning of the telescopes if they were unable to retract properly before the closure of the payload bay doors. The IPS had been used to support a battery of solar-physics instruments during Challenger's Spacelab-2 mission in July 1985, but ASTRO-1 would be the first time it had been employed for deep-sky objects.

As well as the precision-pointing afforded by the IPS, an additional image motion-compensation system had been provided by NASA's Marshall Space Flight Center to better stabilise UIT and WUPPE. This was capable of sensing crew- or thruster-induced movements of the Shuttle and sent data to the telescopes, which automatically readjusted themselves to achieve a stability finer than a single arc-second. This would prove particularly helpful for UIT, which would record its images on sensitive astronomical film.

The telescopes were attached to two Spacelab pallets, which had been joined together to form a short 'train'. Electrical power, cooling and command and data-

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