July 13, 2017 - Critical work has been underway in the lab at LSST’s Project Office in Tucson, AZ: testing of the static supports for LSST’s Primary/Tertiary Mirror (M1M3). When the 8.4-meter mirror is not under active support by the pneumatic actuators, it will rest on an array of wire rope isolators (also referred to as static supports). 355 of these supports will be installed on the mirror cell deck plate. The supports are designed to safely support the mirror under gravity and seismic loading while limiting the motion of the mirror to safe levels.
Each one of the 355 wire rope isolators was tested individually; the featured image shows an isolator undergoing stiffness characterization testing. During this test the isolator is compressed in a test stand, and the compression force and resulting displacement is recorded while the load is slowly increased.
After testing, the wire rope isolators will be sorted and grouped by their stiffness values. The positioning of the isolators under M1M3 will be determined based on optimal load stress reduction. Stiffer units will typically be placed at larger radii from the mirror center, loosely corresponding to the areal distribution of the mirror’s weight. This placement is important to ensure the mirror, which weighs more than 37,000 lbs (16,780 kg), is supported safely whenever it’s not under active support by the pneumatic actuators. This will occur whenever the telescope not actively observing, but is also important in case of unexpected events such as a loss of power to the cell or the telescope facility.