Whew! Hubble Space Telescope back in operation

The Hubble Space Telescope, as it appeared on 25 April 1990 when it was released from the space shuttle Discovery. The legendary observatory has been in operation for 31 years. Image: NASA/Smithsonian Institution/Lockheed Corporation

After weeks of troubleshooting, engineers have resolved a subtle glitch that knocked the Hubble Space Telescope out of action last month, carefully switching over to backup components in its payload computer system and returning the observatory to normal science operations.

“I’m proud of the Hubble team, from current members to Hubble alumni who stepped in to lend their support and expertise,” NASA Administrator Bill Nelson said in a 17 July statement. “Thanks to their dedication and thoughtful work, Hubble will continue to build on its 31-year legacy, broadening our horizons with its view of the universe.”

That’s the good news. The bad news is that Hubble no longer has redundancy in a critical system and a subsequent failure in the payload computer module would be much more difficult to resolve. But for now, Hubble  appears healthy, allowing science observations to resume.

The telescope went into protective “safe mode” 13 June when it ran into a problem with its science instrument command and data handling computer, or SI C&DH, module. When an attempt to restart the computer failed, engineers suspected trouble with memory modules but that, too, turned out to be false.

Hubble is equipped with two fully redundant SI C&DH systems, and troubleshooters first attempted to simply switch over to the backup payload computer. When that did not work, every component in the SI C&DH system was carefully scrutinised to pin down down the culprit.

The team finally identified the problem, blaming the shutdown on a power control unit that regulates voltage in the SI C&DH system. Attempts to reset the original PCU were not successful, so engineers developed a plan to activate the backup unit, along with a backup data formatter.

The switchover was completed 15 July, clearing the way for the resumption of science operations.

“NASA has returned the science instruments on the Hubble Space Telescope to operational status, and the collection of science data will now resume,” NASA said on its website. “This will be the first science data collected since the payload computer experienced a problem on 13 June, which placed the instruments in a safe configuration and suspended science operations.”

The agency said observations that were missed when operations were suspended will be carried out at a later date.