Bearing Keeps Spectrometer Stable in Telescope
- Friday, 01 March 2013
How do you collect data from stars thousands of light years away while positioning a 300-ton, 10-meter telescope to within a fraction of a human hair? You use a high-tech spectrometer called MOSFIRE (Multi-Object Spectrometer For Infra-Red Exploration), rotating on a custom bearing.
With MOSFIRE, astronomers can gather spectra at nearinfrared wavelengths (invisible to the human eye) and even penetrate cosmic dust clouds to investigate the formation of stars and galaxies. The instrument can survey 46 objects at once and switch targets in minutes, instead of the usual one or two days.
MOSFIRE will observe very faint targets more than a hundred times faster than has ever been possible. It is 25 times more light sensitive than other instruments of its kind, and can observe vastly more cosmic objects on any given night. It was commissioned at the W.M. Keck Observatory in Hawaii. The observatory is a scientific partnership of the California Institute of Technology (Caltech), the University of California, and NASA.
The orientation changes constantly, so the bearing used to rotate the telescope must handle many load combinations, both axial and radial. Requirements for the bearing included very little torque variation, the ability to mount it to a structure that is slightly compliant (i.e., not stiff), very little wobble, low maintenance, and the ability for it to fit the existing space. It also had to be able to withstand a harsh environment at 14,000 feet, amidst volcanic cinder dust.
The custom bearing is more slewing ring than thin section type. About two meters in diameter, it features a back-to-back duplex design with integral gearing. The inner race and outer race are thinner than usual for a slewing ring bearing this size, and each race has two ball paths to spread the load and minimize torque variation. Minimizing torque is essential to maintaining the stability needed for reliable data.