What You Saw Was What You

This profile resulted in Columbia flying 'upside down' in an Earth-facing orientation, with the satellite hanging 60 m 'above' her payload bay. By this point,

What you saw was what you got 113

the astronauts - who had watched computer-generated views of the LDEF in simulators for more than a year - saw the real McCoy sitting there waiting to be captured. It was a strange device, measuring 9.1 m long by 4.2 m wide and weighing just over 9,520 kg. At its most basic, it was a bus-sized structure made from aluminium rings and longerons and loaded with trays for 57 materials experiments.

Shortly after the formation of NASA in 1958, scientists began to give serious consideration to developing a satellite that could carry material samples and assess how the harsh environment of low-Earth orbit caused them to degrade over time. By 1970, these ideas had acquired a name: the Meteoroid and Exposure Module (MEM), which it was proposed would be carried aloft by the Shuttle - then scheduled to make its first flight in 1978 - and retrieved a few months later. As the name implies, its primary focus was the impact of micrometeorites on satellites and how best to protect them.

By the mid-1970s, the MEM had been renamed the LDEF and contracts for its development were granted to NASA's Langley Research Center in Hampton, Virginia. The basic 12-sided structure was complete by 1978 and, after tests, was kept at Langley until a Shuttle flight became available. By this point, its objectives had expanded from micrometeoroid research to studies of changes in material properties over time, performance tests of new spacecraft systems, evaluating power sources and conducting crystal growth and space physics investigations.

The satellite was designed to be reusable and adaptable for differing lengths, if desired, although ultimately it would fly only once. Its length was divided equally between six bays for the experiment trays, with a central 'ring' at the midpoint connected by longerons to the endframes. Aluminium 'intercostals' linked each longeron to adjacent rows of longerons on each side and removable bolts joined the longerons to the endframes and intercostals. This meant that the LDEF could be made 'shorter' or 'longer' if a mission required it. Experiment trays were then clipped into the rectangular openings between the longerons and intercostals.

Two RMS grapple fixtures were provided on the satellite: one to allow it to be picked up by the robotic arm for deployment and retrieval and a second to send signals to initiate the experiments. The LDEF had no attitude-control system of its own and what you saw was what you got: a passive experiment container with no manoeuvring capabilities. It was designed to remain in orbit by being placed into a 'gravity-gradient' attitude, with one end facing Earthwards, which made an onboard propulsion system unnecessary. This also freed it from acceleration forces or contamination caused by thruster firings.

The orientation of the satellite also meant that the two 'ends' would be subjected to a unique thermal environment, although all parts of the LDEF were subjected to daily temperature changes as the Sun 'rose' and 'set' every 90 minutes and solar angles changed annually. Heat management was accomplished by coating the interior surfaces with high-emissivity black paint, which kept thermal gradients across the structure to a minimum and maximised heat-transfer across the LDEF's body. The experiments were also spread evenly to equalise thermal properties across the satellite.

Bonnie Dunbar gently lowers the LDEF into Columbia's payload bay after retrieval.

Eighty-six trays - 72 around the circumference, six on the Earth-facing end and eight on the space-facing end - accommodated 57 investigations. The 1.3 m x 86 cm trays came in several depths and housed experiments weighing up to 90 kg. These covered four disciplines: (1) Materials and Structures, (2) Power and Propulsion, (3) Science and (4) Electronics and Optics. They captured interstellar gas atoms to understand the Milky Way's formation, observed cosmic rays and micrometeoroids, studied shrimp eggs and tomato seeds and investigated the impact of atomic oxygen on different materials, including solar cells.

It was therefore with added urgency that Columbia returned to flight operations in August 1989, because she had been designated as the Shuttle that would retrieve the wayward satellite. By the time Brandenstein's crew finally set off in January of the following year, the LDEF was within weeks of being lost forever, having reached

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