Although a series of tests, including attempts to restart and reconfigure the computer and backup computer, were unsuccessful, the information gathered from those tests led the Hubble team to conclude that the problem could be in the Power Control Unit (PCU), which powers the payload computer.
On July 15th, NASA has successfully switched to backup hardware on the Hubble Space Telescope. To allow the telescope to function, the backup PCU was brought online, and other pieces of hardware were swapped to their backup versions.
The team is currently monitoring the hardware to check that everything is working properly, and has already begun the process of resuming operations on the science instruments that have been put in safe mode.
According to NASA, these steps are expected to take more than a day because the team must ensure that the instruments are working at stable temperatures in space. Before returning to its science mode, the team will also conduct some initial calibration on these instruments.
Hubble will be joined in space by the James Webb Space Telescope (JWST) later this year. Unlike its 30-year-old buddy, Webb will orbit Earth at a greater distance (around 930,000 miles/ 1,500,000 km away from our planet). It will be equipped with improved infrared resolution and sensitivity, allowing the space agency to peer into the most distant objects in the universe.