page_title: Hubble Space Telescope
section_title: Gyroscope rotation sensors
hierarchical_section_title: Hubble Space Telescope / Equipment failures / Gyroscope rotation sensors
caption_attribution_description: English: This image, taken with the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope, shows the newly discovered planet, Fomalhaut b, orbiting its parent star, Fomalhaut. The small white box at lower right pinpoints the planet's location. Fomalhaut b has carved a path along the inner edge of a vast, dusty debris ring encircling Fomalhaut that is 21.5 billion miles across. Fomalhaut b lies 1.8 billion miles inside the ring's inner edge and orbits 10.7 billion miles from its star. The inset at bottom right is a composite image showing the planet's position during Hubble observations taken in 2004 and 2006. Astronomers have calculated that Fomalhaut b completes an orbit around its parent star every 872 years. The white dot in the center of the image marks the star's location. The region around Fomalhaut's location is black because astronomers used the Advanced Camera's coronagraph to block out the star's bright glare so that the dim planet could be seen. Fomalhaut b is 1 billion times fainter than its star. The radial streaks are scattered starlight. The red dot at lower left is a background star. The Fomalhaut system is 25 light-years away in the constellation Piscis Australis. This false-color image was taken in October 2004 and July 2006.
context_page_description: The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, well known both as a vital research tool and as a public relations boon for astronomy. The Hubble telescope is named after astronomer Edwin Hubble and is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.
  Hubble features a 2.4-meter mirror, and its four main instruments observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. Hubble's orbit outside the distortion of Earth's atmosphere allows it to capture extremely high-resolution images with substantially lower background light than ground-based telescopes. It has recorded some of the most detailed visible light images, allowing a deep view into space. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe.
  The Hubble telescope was built by the United States space agency NASA with contributions from the European Space Agency.
context_section_description: HST uses gyroscopes to detect and measure any rotations so it can stabilize itself in orbit and point accurately and steadily at astronomical targets. Three gyroscopes are normally required for operation; observations are still possible with two or one, but the area of sky that can be viewed would be somewhat restricted, and observations requiring very accurate pointing are more difficult. In 2018, the plan is to drop into one-gyroscope mode if less than three working gyroscopes are operational. The gyroscopes are part of the Pointing Control System, which uses five types of sensors (magnetic sensors, optical sensors, and the gyroscopes) and two types of actuators (reaction wheels and magnetic torquers). Hubble carries six gyroscopes in total.
  After the Columbia disaster in 2003, it was unclear whether another servicing mission would be possible, and gyroscope life became a concern again, so engineers developed new software for two-gyroscope and one-gyroscope modes to maximize the potential lifetime. The development was successful, and in 2005, it was decided to switch to two-gyroscope mode for regular telescope operations as a means of extending the lifetime of the mission. The switch to this mode was made in August 2005, leaving Hubble with two gyroscopes in use, two on backup, and two inoperable. One more gyroscope failed in 2007.
  By the time of the final repair mission in May 2009, during which all six gyroscopes were replaced (with two new pairs and one refurbished pair), only three were still working. Engineers determined that the gyroscope failures were caused by corrosion of electric wires powering the motor that was initiated by oxygen-pressurized air used to deliver the thick suspending fluid. The new gyroscope models were assembled using pressurized nitrogen and they should be much more reliable. In the 2009 servicing mission all six gyroscopes were replaced, and after almost ten years only three gyroscopes failed, and only after exceeding the average expected run time for the design.
  Of the six gyroscopes replaced in 2009, three were of the old design susceptible for flex-lead failure, and three were of the new design with a longer expected lifetime. The first of the old-style gyroscopes failed in March 2014, and the second in April 2018. On October 5, 2018, the last of the old-style gyroscopes failed, and one of the new-style gyroscopes was powered-up from standby state. However, that reserve gyroscope did not immediately perform within operational limits, and so the observatory was placed into "safe" mode while scientists attempted to fix the problem. NASA tweeted on October 22, 2018, that the "rotation rates produced by the backup gyro have reduced and are now within a normal range. Additional tests [are] to be performed to ensure Hubble can return to science operations with this gyro."
  The solution that restored the backup new-style gyroscope to operational range was widely reported as "turning it off and on again". A "running restart" of the gyroscope was performed, but this had no effect, and the final resolution to the failure was more complex. The failure was attributed to an inconsistency in the fluid surrounding the float within the gyroscope (e.g., an air bubble). On October 18, 2018, the Hubble Operations Team directed the spacecraft into a series of maneuvers—moving the spacecraft in opposite directions—in order to mitigate the inconsistency. Only after the maneuvers, and a subsequent set of maneuvers on October 19, did the gyroscope truly operate within its normal range.
caption: Hubble views the Fomalhaut system. This false-color image was taken in October 2004 and July 2006 with the Advanced Camera for Surveys.
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