The Hubble Space Telescope is expected to return to normal scientific operations soon, after its back-up gyroscope was brought into service, with engineers able to reduce unusually high rotation rates down to "within an expected range".
Hubble will therefore return to normal operations after additional tests have been conducted. The gyroscope measures the speed at which the spacecraft is turning, and therefore helps the telescope remain stable, to point in the right direction and lock-on to new targets.
A wheel inside the gyro spins at a constant rate of 19,200 revolutions per minute. This wheel is mounted in a sealed cylinder, which is suspended in a thick fluid
The Hubble Space Telescope was put into ‘safe mode' on Friday 5 October after one of its three on-board gyroscopes failed. Six new gyroscopes were installed during a Servicing Mission in 2009 and, while Hubble requires three operating at any one time for maximum operational efficiency, it can get by with just one.
The gyro that failed had been exhibiting end-of-life behaviour for approximately a year, NASA revealed, and its failure was not unexpected.
However, the back-up gyroscope that scientists had brought-up to replace the failed gyro was rotating at too high a rate, forcing scientists to devise a way to fix it, if possible.
A restart of the device was performed last week: "This procedure turned the gyro off for one second, and then restarted it before the wheel spun down. The intention was to clear any faults that may have occurred during startup on 6 October, after the gyro had been off for more than seven-and-a-half years. However, the resulting data showed no improvement in the gyro's performance," explained NASA.
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
The team then conducted a series of manoeuvres with Hubble in a bid to clear any blockage or debris that might be causing the problem. This, it seems, has helped to clear the cause of the problem, with a "significant reduction" in the unusually high rates of spin.
"Hubble then executed additional manoeuvres to make sure that the gyro remained stable within operational limits as the spacecraft moved. The team saw no problems and continued to observe the gyro through the weekend to ensure that it remained stable," added NASA.
The gyroscopes, of course, are not an off-the-shelf part, and are integral to Hubble's operations.
The way the gyroscopes work are as follows, according to 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."
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