Two-Gyro Science

HST's normal operational mode utilizes three gyros out of the six onboard the spacecraft to provide a highly accurate attitude reference as part of the pointing control system (PCS). Over time these gyros eventually fail leaving the spacecraft with less redundancy and, eventually, with less than the number of gyros required (3) for the PCS to operate normally.

The Two-Gyro Science (TGS) mode is a means of providing spacecraft attitude control and slew capability, in the case of only two operational gyros, with sufficient accuracy to continue science operations.

TGS is a contingency mode targeted for use in the event that the HST is in a two-gyro condition prior to Servicing Mission 4 and/or at HST end-of-life. It is also a degraded mode in the sense that science operations can continue, but with higher jitter and less efficiency and flexibility than with normal operations using three gyros. Certain classes of current science operations will likely be heavily constrained or not possible in Two-Gyro mode.

Presentations