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acquisition services were provided by the igloo, mounted on the front pallet. Behind the pallets was a separate support structure, known as a Two-Axis Pointing System (TAPS), which held the BBXRT. Like the IPS, it was capable of manoeuvring its telescope backwards and forwards and side-to-side; but unlike the ASTRO-1 instruments, it was controlled remotely from the ground. The astronauts' involvement would be little more than turning it on and off and monitoring its health.

Built by NASA's Goddard Space Flight Center - from where the telescope was operated - the BBXRT observed high-energy celestial targets, including active galaxies, quasars and supernova remnants; particularly that of Supernova 1987A. Prior to each observation 'run', it was intended that stored commands would be loaded into the telescope's computer and when the crew manoeuvred Columbia to face a celestial target, TAPS automatically aligned the BBXRT with that target.

ASTRO-1 would become the first scientific mission to be managed from the Marshall Space Flight Center's new Spacelab Mission Operations Control Facility, replacing JSC's Payload Operations Control Center (POCC) used on earlier flights. The new facility was capable of sending commands directly to the Shuttle, monitoring the ultraviolet telescopes, directing their observations, receiving and analysing data, adjusting schedules to take advantage of unexpected discoveries and working with the crew to resolve hardware problems. Each of these capabilities would prove instrumental in the mission's success when it eventually took place.

The complete ASTRO-1 payload - including the three ultraviolet telescopes, pallets, IPS and igloo - weighed a whopping 7,830 kg, while the BBXRT and TAPS were a little over half as much at 3,920 kg. This would prove to be one of the heaviest research facilities ever carried into orbit by the Shuttle. Further tests of the combined system were conducted throughout the early spring of 1990 and on 20 March it was loaded into Columbia's payload bay. Four years after ASTRO-1 should have been observing Halley's Comet, it seemed that the mission would finally get to fly.

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