After days of testing and unsuccessful attempts to get the Hubble back up and running, NASA engineers seem to be able to pinpoint the cause of the failure.
The agency said that the failure is related to the payload computer: it is located in the scientific instruments control and data processing unit (SI C&DH). He oversees and coordinates the operation of Hubble’s scientific instruments. When the payload computer stopped working, all Hubble technology automatically went into a secure configuration.
A series of multi-day tests that included attempts to restart and reconfigure the computer and the backup computer were unsuccessful, but the information gathered from these actions allowed the Hubble team to determine that the possible cause of the problem was the Power Control Unit (PCU).
The PCU is also located in the SI C&DH block. This provides a stable voltage supply to the payload computer hardware. In addition, there is a protective circuit that monitors voltage parameters. The failure could occur in one of these two components.
If the voltage drops below or exceeds acceptable levels, this secondary circuit tells the payload computer to shut down. The analysis of the command shows that either the voltage level on the regulator is outside the permissible levels (and because of this, the secondary protection circuit has turned off), or the secondary protection circuit has become worse over time and is stuck in one state.
The switchover will begin on July 15, and if successful, it will take several days to fully return the observatory to normal scientific work.