Hubble telescope spins round, fixes self

It hasn’t been the best month for the Hubble Space Telescope.

During the first week of October, one of the spacecraft’s three gyroscopes failed. The giant telescope needs the devices to measure turning speeds and to zero in on the things in space it observes and photographs.

In a statement, NASA reassured the public that the breakdown was expected, saying the gyro “had been exhibiting end-of-life behaviour for approximately a year” and, in any case, “two other gyros of the same type had already failed.”

To replace it, NASA engineers powered up a backup gyroscope that had been dormant since early 2011. They were heartened, at first. The gyroscope began spinning despite not being used for 71/2 years. However, it sent back readings that were clearly too high.

The discrepancy was “similar to a speedometer on your car continuously showing that your speed is 100 miles per hour faster than it actually is,” NASA said. “It properly shows when your car speeds up or slows down, and by how much, but the actual speed is inaccurate.”

Engineers concluded the problem must have been some kind of mechanical obstruction. Vowing to fix it, NASA kept the telescope in “safe mode,” limiting its operations in the same way a computer in that mode operates at bare-bones settings.

Keeping the telescope in safe mode also meant “we were not doing science,” Hubble Operations project manager Patrick Crouse told The Washington Post. Days passed.

NASA teams ran tests, reviewed the flight software and considered what they could do to remedy the problem with as little damage as possible to their prized (and expensive) telescope.

On Oct. 16, the Hubble team even attempted a “running restart,” turning the problematic gyroscope off for one second, then back on again. Unfortunately, the “have you tried powering it off and on?” approach — long favoured as a first-resort by technical support staff on Earth — didn’t work in space. Would that it were that easy, Crouse said.

Instead, what appeared to work was repeatedly turning the entire Hubble spacecraft to see if it would “dislodge” anything that was blocking the gyroscope in question.

The repeated manoeuvres seemed to work, with the gyro reporting rotation rates that were back to normal — much to the relief of Hubble engineers, Crouse said.