The gyro spin directions are referred via a quartz block to the telescope, and the telescope to the guide star. Like the rest of the instrument, the telescope is made of fused quartz .
Mechanical stability comes from having fused quartz, in zero gravity, cold.
Distortion from temperature gradients, a near-fatal problem at ordinary satellite temperatures, vanishes. Another factor in the telescope's exceptional stability is that its twenty separate component parts are all held together by a technique known as optical contacting . The gyroscope and telescope output signals are not angles but voltages. That fact raises two issues. Matching is achieved by a technique known as dither .