Two Gyro Science Mode

The Hubble Space Telescope was originally designed to use three rate-sensing gyroscopes to prvide fine pointing control of the observatory during science observations. In order to conserve the lifetime of the HST gyros, one of the functioning gyros was turned off on 28 August 2005 and a new attitude control system that functions with only two gyros was activated. In this mode, two gyros used in combination with the Fine Guidance Sensors provide fine-pointing information during science observations.

		Read These
		Two Gyro Summary (pdf): Read this to get a quick understanding (2 pages). Two Gyro Handbook: Read Chapters 1 and 2 before proposing (33 pages Ch. 1&2; 73 pages total). Instrument Reports: Read these for results from the February on-orbit tests.

Scheduling Aids A Narrated Sky Availability Movie shows how sky availability is affected in Two Gyro Mode. The Available Science Time and Orientation Tool provides plots showing available orientations and observing times throughout the year for two gyro operations. A Detailed Visibility Tool provides higher resolution plots showing available orientations and observing times in 11 day windows.

Two Gyro FAQs Coronagraphy Moving Targets Mosaics Snapshots Guide Star Availablilty Targets of Opportunity TIme Series Observations   Scheduling Decision Tree (pdf) Web Tool Plots (pdf)

Warning: Information on this page is based on the February on-orbit test, and is expected to be valid for actual operations. However, as HST has only recently begun two gyro operations, further on-orbit experience may result in revisions to the information presented here. See the Site Change Log for a summary of the additions and changes to the information on this site.