Hubble 'scope gyro drama: Hey, NASA, have you tried turning it off and on again? Oh, you did. And it worked? Cool
Just don't let it restart to install updates...
The classic “turn it off and turn it back on” strategy has worked once again for NASA, in that it may return the Hubble Space Telescope to active duty.
On October 5, the venerable orbiting 'scope glitched out, and automatically put itself into hibernation to avoid any self-inflicted damage. Since then, its human controllers have been working on a strategy to get it back on track so it can return to scanning the heavens.
Those NASA boffins eventually worked out one of gyroscopes had failed. If everything else had worked properly, that shouldn't have been a problem because Hubble has two in-service gyros and one available as a backup. In other words, there was a backup gyro to step in for a failed in-service part.
Spinning faster than Sarah Sanders
When the scientists spun up that spare to take over from the dud in-service gyro, however, there was a problem: the replacement was spinning too fast to be useful. That forced the scientists to decide between fixing the dodgy spare, or operate on a single gyro – the lone remaining working in-service one – the latter option reducing the precision of the instrument.
In its latest mission update, dated October 22, NASA said it opted to turn off and on again the borked spare, and it looks as though that did the trick. Last Tuesday, the operations team tried a “running restart” of the buggy backup gyro, which had been otherwise switched off for seven and a half years: “This procedure turned the gyro off for one second, and then restarted it before the wheel spun down.”
That, alas didn't clear the fault, so the Hubble team tried a different approach: they turned Hubble back and forth while repeatedly restarting the gyro. Bear in mind the telescope is circling Earth at a distance of 340 miles.
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“On Oct 18, the Hubble operations team commanded a series of spacecraft maneuvers, or turns, in opposite directions to attempt to clear any blockage that may have caused the float to be off-centre and produce the exceedingly high rates," the American space agency's eggheads explained. "During each maneuver, the gyro was switched from high mode to low mode to dislodge any blockage that may have accumulated around the float."
As a result of that technique, the NASA scientists noticed a “significant reduction” in the gyro's previously high-speed spin rate, so they ran a repeat of the exercise – and that appeared to have “cleared the issue.”
Throughout the weekend, NASA said, the backup gyro remained stable, so staff have commenced a series of engineering tests – moving to point at targets, locking onto them, and fine tuning its positioning with high precision. If successful, Hubble will return to normal science operations as soon as possible with two working gyroscopes. ®