NASA Langley Research Center
Hampton, Virginia

	Langley Home Page
	Space Environments &Technology Archive System Home Page
	Space Environments &Effects Home Page
	NASA Home Page

Structure

In cross-section, LDEF was a dodecagon or a 12-sided regular polygon that was 14 feet wide. The 12 flat sides accomodated experiments, while the nearly cylindrical shape fit efficiently into the Shuttle's payload bay. The structure was composed primarily aluminum 6061-T6, with some structural elements composed of steel and titanium. LDEF's 30-foot length was divided equally between six bays for the experiment trays, with a center ring midway along the length that was constructed of aluminum with welded joints. Aluminum longerons connected the center ring to the end frames, and aluminum intercostals connected each longeron to the adjacent rows of longerons on either side. Bolts were used to join the longerons to the end frames and intercostals; this allowed flexibility to make the LDEF larger or smaller in length. Experiment trays were attached to the LDEF structure with bolted clips or clamps, and fit into the rectangular areas bordered by the longerons and intercostals. Diagonal tubular elements were located in the interior of LDEF and extended between the center ring and the two end frames to provide stiffness. The LDEF structure was constructed at NASA Langley Research Center between 1976 and 1978.

For attachment to the Shuttle's payload bay, LDEF had two main steel trunnion pins attached to opposing sides of the center ring, on rows three (3) and nine (9). A third pin was attached to the center ring adjacent to row six (6), and fit into the deck of the payload bay. The fourth attachment fixture was the walking beam, centered on the Earth-end frame. The walking beam, also referred to as the end-support beam, could be rotated slightly. No more than three of these points contacted the Shuttle in any plane; in this way their fit was best assured if LDEF were to have undergone dimensional changes in space.

Two grapple fixtures were located on LDEF. The passive (flight releasable) grapple was used by the Shuttle's Remote Manipulator System (RMS) to deploy and retrieve LDEF. The active (rigidize sensing) grapple was used to send an electronic signal to initiate the19 experiments that had active data and power systems.

A viscous magetic damper was located at the interior center of the space-end frame. Using the Earth's magnetic field and a viscous fluid, its purpose was to damp out initial oscillations of LDEF associated with its placement into orbit. The damper contained two concentric spheres. The outer sphere was rigidly attached to the LDEF end frame. The inner sphere, containing a permanent magnet and bellows, was filled with helium, and was separated from the outer sphere by a layer of silicone oil. The outer sphere had a pyrolytic graphite line for diamagnetic centering. As the magnet aligned with the Earth's magnetic field, the flow resistance of the silicone oil damped movement of the outer sphere and the rest of the LDEF structure.

LDEF underwent flight qualification static and dynamic tests at LaRC prior to its being placed in storage at LaRC in 1979.

Back

LDEF Archive System Home Page