It has been a harrowing few weeks for the
Hubble Space Telescope, but
NASA believes it is one step closer to restoring the instrument to full functionality. NASA engineers initially feared the telescope’s backup gyroscope was busted, which would have limited Hubble’s ability to observe the universe. However, a series of deceptively simple procedures seems to have knocked some sense into the gyro. We’re not out of the woods yet, but things are looking good.
NASA decided to put Hubble in hibernation mode after one of its remaining gyroscopes failed. Hubble needs three active gyroscopes to detect movement and ensure it’s pointed in the right direction. With only two operational gyros, NASA turned to Hubble’s last remaining backup unit. NASA replaced all six of Hubble’s gyroscopes in the final servicing mission almost a decade ago. Three of the gyroscopes were an old design, and three of them were a new, more robust design. The operating gyroscope that failed was the last of that old design, but the final “new” gyro had been off for more than seven years, and it didn’t want to start up.
Hubble’s gyroscopes are suspended in sealed chambers of highly viscous fluid. They spin at 19,200 rpm, allowing the telescope to detect even tiny movements via angular momentum. When NASA tried to activate the backup gyroscope, it reported an extremely high rotation rate that didn’t match the design spec. NASA first tried the tried-and-true method of turning it off and on again. From the ground, Hubble operators were able to spin the gyro up, turn it off, and then flip it back on before it had completely spun down. They hoped this would clear any blockage that caused the abnormal readings. That didn’t work, so NASA brought out the big guns: it shook the gyroscope, too.
NASA describes the process of fixing the gyroscope in lofty terms, but it’s not that much different than your first instinct when something breaks. First, it told Hubble to execute a series of maneuvers in opposite directions (i.e. shaking). While the telescope jiggled, NASA also flipped the gyroscope from low to high mode to clear any obstructions. The agency reports this appears to have worked. The backup gyroscope is again reporting the correct rotation speed.
NASA still has some testing to do, but Hubble will likely be spared from limping along in single-gyroscope mode (NASA said it would use a single gyro if it only had two remaining to extend Hubble’s life). All three operational gyroscopes are the newer design, so the telescope could continue operating at full capacity for years to come. Hopefully, it can survive until the successor James Webb Space Telescope launches in the early 2020s.