On July 16, after 35 days of rigorous efforts, NASA scientists successfully powered on the backup payload computer of the Hubble Space Telescope. Scientists were also successful in switching to backup hardware and have started the process to recover all the instruments from safe mode. Hubble’s payload computer, which coordinates and controls operations of the scientific instruments onboard the space telescope, had stopped working on June 13.
Here is how the operations team at NASA achieved it:
June 13: Hubble’s payload computer stops. No “keep-alive” signal is relayed to the main computer. The main computer puts equipment into safe mode to avoid damage.
June 14: Attempt to restart the payload computer fails. Initial data show memory modules could be at fault. Tests planned.
June 16: Preparations for testing the backup memory module begin. Scientists run tests to find if a degrading memory module can be the culprit.
June 17: Commands to initiate the backup memory module fail to complete. Attempts to bring both modules — current and backup — online, fail. Scientists fail to obtain more diagnostic data on the modules. More tests planned.
June 22: Test results indicate that some hardware other than memory modules was at fault. Investigation continues.
June 23, 24: Backup computer turned on, but memory error not fixed. The team tries many combinations including both payload computers — the primary and the backup computer. Scientists suspect the issue was in Command Unit/Science Data Formatter (CU/SDF) or power regulator.
June 30: Issue narrowed down -it was either Command Unit/Science Data Formatter (CU/SDF) or power regulator. The job of CU/SDF is to send and format commands and data. The power regulator in the Power Control Unit ensures a steady flow of five volts. Preparations to switch to backup hardware begin.
July 14: Issue identified: Either the voltage level was outside of acceptable levels or a secondary circuit, which verifies voltage levels and asks to stop if it does not meet the acceptable levels, was stuck in inhibit state because of degradation. Switching to the backup Power Control Unit is required.
July 16: Successfully switched to the backup power control unit. Turned on the payload computer. Scientists are monitoring if everything is working properly. The process of recovering instruments from safe mode begins.