MGM fact sheet: hardware

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Mechanics of Granular Materials

Hardware

The heart of the second MGM experiment is a set of six test cells, each containing a sleeve of 1.3 kg (2.8 lbs.) of sand, 7.5 cm in diameter by 15 cm tall (3 x 6 in.).

These experiments use Ottawa F-75 banding sand, a natural quartz sand (silicon dioxide) with fine grains (0.1 to 0.3 mm diameter) and little variation in size. Because Ottawa sand is widely used in civil engineering experiments and evaluations, its use on MGM will allow results to be compared directly with results from experimental results already obtained on Earth. The soil specimen is contained in a latex sleeve that is 0.3 mm thick and printed with a grid pattern so cameras can record changes in shape and position.

Left: One of three MGM test cells after flight on STS-79 and before impregnation with resin. Note that the sand column has bulged in the middle, and that the top of the column is several inches lower than the top of the plastic enclosure. Links to 1200x2013-pixel, 992K JPG. Credit: University of Colorado at Boulder.

Right: An MGM cell installed in its locker so video cameras have a clear view of the specimen. Links to 595x895-pixel, 264K JPG. Credit: NASA/Kennedy Space Center.

Each specimen is contained in a test cell shaped like an equilateral prism and comprising a Lexan jacket sandwiched between metal end plates connected by guide rods. Within the Lexan jacket the cell is filled with water and pressurized to keep the specimen confined and stable during launch and re-entry. Special platens of polished tungsten carbide (for hardness and low friction) are placed on the top and bottom ends of the specimen. An electric stepper motor on top of the test cell moves the top platen up and down. A load cell measures the force imparted to the specimen.

During the experiment, a test cell is held on a rigid test/observation pad mounted between an array of three CCD cameras and banks of small light-emitting diodes. The MGM video control system electronically interleaves the images for a video recorder. The systems are controlled by the Payload General Support Computer (PGSC), a laptop computer operated by the flight crew.

MGM hardware was designed and developed by Sandia National Laboratories, U.S. Department of Energy, in Albuquerque, N.M.

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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack