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The Hubble Space Telescope has gone through its share of gyroscopes in its 34-year history in space. Astronauts replaced the gyros during the last servicing mission in 2009, bringing it back up to six (three with three spares), but they only last so long. Last week, HST went into safe mode because one of the gyros experienced fluctuations in power. NASA paused the telescope\u2019s science operations today to investigate the fluctuations and perhaps come up with a fix.<\/p>\n
With this one gyro experiencing problems, only two of the gyros remain fully operational. HST works best with three gyros, and so engineers are working to understand the issue and hopefully figure out a way to fix it remotely. However, several years ago, engineers figured out a way to still conduct science operations with only a single gyro.<\/p>\n
<\/p>\n HST entered safe mode on April 23, 2024 when the one gyro sent faulty readings. This particular gyro also caused Hubble to enter safe mode last November after returning similar faulty readings. The gyroscopes are part of Hubble\u2019s Pointing Control System, which includes three Fine Guidance Sensors, reaction wheels and the gyros. This allows Hubble to track stars with incredible accuracy, helping the telescope find its way as it scans the heavens, as well as keep Hubble locked onto to its targets.<\/p>\n To work correctly, Hubble must be able to stay focused on a target without deviating more than 7\/1000th of an arcsecond, or about the width of a human hair seen at a distance of a mile.<\/p>\n Hubble team created a contingency plan in preparation for a time when the spacecraft might find itself with less than three working gyros again. The team developed a two-gyro mode that substitutes other sensors for one missing gyro. Although less efficient, two-gyro mode allows Hubble to continue collecting ground-breaking science data.<\/p>\n NASA said that Hubble gyros fail over time, usually because of \u201cwear and tear\u201d of thin (less than the width of a human hair), metal wires, called flex leads that carry power in, and data out, of the mechanism. Hubble\u2019s flex leads pass through a thick fluid inside the gyro. Over time, the flex leads begin to corrode and can physically bend or break.<\/p>\n \n