In brief: On Friday, NASA announced that it has finally restored the Hubble Space Telescope (HST) to semi-operational status. The news comes after the craft spent over a month in safe mode. The telescope is running on its backup payload computer and will resume normal operations once NASA has the rest of its systems back online.
Last month, on June 13, the HST's main payload computer went down, and NASA engineers could not get it to reboot past safe mode. Technicians thought the problem might have something to do with the 31-year-old orbiting telescope's memory module. However, it turned out to be the power control unit (PCU).
The Hubble Space Telescope backup payload computer was successfully brought online after a successful switch to backup hardware. Following a short checkout period, the science instruments will be brought back to operational status.https://t.co/Wca2Puz4mT--- Hubble (@NASAHubble) July 16, 2021
The HST's PSU supplies five volts of electricity to the system. If the power fluctuates or fails, the telescope pauses operations until consistent power is restored. NASA made several attempts to reboot the PSU without success. So the team switched to the backup payload computer as a last resort, since it is a very "complex and risky" process.
The initialization of the backup was a success, and NASA engineers will spend the rest of the day rebooting the HST's other equipment. Once everything is running in a stable state, the telescope will resume normal scientific operations. Running on backup hardware should not pose a significant problem as the observatory is nearing the end of its life anyway.
Its duties will soon be mostly taken over by the much more powerful, albeit delay-plagued James Webb Space Telescope (JWST), scheduled to launch on October 31 this year, barring any other setbacks. The two will operate in tandem for a while until the HST fails or NASA decides to retire it.