What is JWST doing to ensure that its gyros last the full mission?
The gyroscopes on HST and Chandra are mechanical devices dependent on bearings for their function, and they face problems typical of such designs. JWST has adopted a different gyroscope technology. The “Hemispherical Resonator Gyroscope” (HRG) uses a quartz hemisphere vibrating at its resonant frequency to sense the inertial rate. The hemisphere is made to resonate in a vacuum, and the hemispheres rate of motion is sensed by the interaction between the hemisphere and separate sensing electrodes on the HRG housing. The result is an extremely reliable package with no flexible leads and no bearings. The internal HRG operating environment is a vacuum, thus once the gyroscope is in space any housing leaks would actually improve performance. Stress analyses of HRGs show this design has a “mean time before failure” of 10 million hours. As of June 2006, this type of device had accumulated more than 7 million hours of continuous operation in space without a failure. This new technology eliminat
