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Backup Hubble gyroscope encounters anomaly during recovery efforts

hubble space telescope 2009

The Hubble Space Telescope as seen by the departing STS-125 crew after a week servicing the observatory in 2009. Photo Credit: NASA

It has been a little more than two weeks since the Hubble Space Telescope had one of the gyroscopes (gyro) that determine the speed at which the observatory is turning fail. Efforts to return Hubble to service encountered a slight hiccup.

The gyro that malfunctioned on Friday, Oct. 5 had its tasks handed off to a backup gyro. Things didn’t go off without a hitch however, the backup gyro incorrectly returned extremely high rotation rates.

The backup gyro has since calmed down and has begun transmitting rates within normal parameters. Engineers aren’t taking any chances with the nearly 30-year-old spacecraft and plan to continue running tests. 

Each gyro helps enable Hubble to aim precisely at the desired celestial “target” by measuring the speed that the telescope is turning. These gyros must endure the rigors of space and still operate as planned. As described by NASA:

“A wheel inside the gyro spins at a constant rate of 19,200 revolutions per minute. This wheel is mounted in a sealed cylinder, called a float, which is suspended in a thick fluid. Electricity is carried to the motor by thin wires, approximately the size of a human hair, that are immersed in the fluid. Electronics within the gyro detect very small movements of the axis of the wheel and communicate this information to Hubble’s central computer. These gyros have two modes — high and low. High mode is a coarse mode used to measure large rotation rates when the spacecraft turns across the sky from one target to the next. Low mode is a precision mode used to measure finer rotations when the spacecraft locks onto a target and needs to stay very still.”

The Hubble operations team recognized the problem and essentially rebooted the backup gyro. Similar in some ways to restarting your home computer, technicians turned the gyro off for a second and then reactivated it before the wheel had spun down. By doing this the team hoped that, similar to a computer, their actions would result in the clearing of whatever was causing the problem. The restart was conducted on Oct. 16 about a week and a half after the initial startup which took place on Oct. 6. 

The restart did not have the desired results. So, two days after the reboot was attempted, Hubble was given a series of commands to turn in opposite directions in an effort to clear whatever was causing the problem. Each time Hubble was ordered to carry out one of these moves the Hubble team turned the gyro from “high mode” to “low mode.”

After continuing to go through these procedures, whatever was causing the high rotation rates appears to have been cleared away with the backup gyro operating normally in both high and low mode. In order to ensure that the problem was put behind them, operators on the ground continued to put the telescope through its paces for the next couple of days.

The backup gyro will likely be given some leeway for its glitch considering that it has laid dormant for seven and a half years. With its 30th on orbit anniversary approaching, scientists are anxious to continue gaining data from the veteran spacecraft and it appears that Hubble is on the road to recovery.





Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

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