ann1812 — Announcement

Update on the Hubble safe mode

17 October 2018

NASA continues to work toward resuming science operations of the NASA/ESA Hubble Space Telescope after the spacecraft entered safe mode due to a failed gyroscope on Friday 5 October (ann1811).

Following the gyroscope failure, the Hubble operations team turned on a backup gyroscope on the spacecraft. However, that gyroscope did not perform as expected, reporting rotation rates that are orders of magnitude higher than they actually are. Since then tests were conducted to assess the condition of that backup gyroscope. The tests showed that the gyroscope is properly tracking Hubble’s movement, but the rates reported are consistently higher than the true rates.

When Hubble turns across the sky from one target to the next, the gyroscopes are put into a coarser (high) mode. In this high mode it may be possible to subtract out a consistent large offset to get an accurate reading. However, after the large turns are over, the spacecraft attempts to lock onto a target and stay very still. For this activity, the gyroscopes go into a precision (low) mode to measure very small movements. The extremely high rates currently being reported exceed the upper limit of the gyroscopes in this low mode, preventing the problematic gyroscope from reporting the spacecraft’s small movements.

An anomaly review board that consists of gyroscope engineers, Hubble operations personnel, flight software engineers and other experts was formed last week to identify the cause of this behaviour and determine what solutions can be implemented from the ground to correct or compensate for it.

If the team is successful in solving the problem, Hubble will return to normal, three-gyroscope operations. If it is not, the spacecraft will be configured for one-gyroscope operations, which will still provide excellent science well into the 2020s, enabling it to work alongside the NASA/ESA/CSA James Webb Space Telescope and continue groundbreaking science.

Safe mode places the telescope into a stable configuration that suspends science observations and orients Hubble's solar panels toward the Sun to ensure that the power requirements are met. Hubble will remain in this configuration until ground control can correct or compensate for the issue. The rest of the spacecraft and its instruments are still fully functional and are expected to produce excellent science for years to come.

During Servicing Mission 4 in 2009, astronauts replaced all six gyroscopes on Hubble. Three gyroscopes have since failed after achieving or exceeding the average runtime for a Hubble gyroscope. When fewer than three operational gyroscopes remain, Hubble will continue to make scientific observations in a previously developed and tested mode that uses just one gyroscope in order to maximize the observatory’s lifetime.

Originally required to last 15 years, Hubble has now been operating for more than 28. The final servicing mission in 2009, expected to extend Hubble’s lifetime an additional 5 years, has now produced more than 9 years of science observations.



Felicia Chou
Office of Communications
NASA Headquarters, Washington D.C.

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500

About the Announcement



Hubble Space Telescope sporting new solar arrays during SM3B
Hubble Space Telescope sporting new solar arrays during SM3B

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