The National Aeronautics and Space Administration (NASA), has discovered the most likely cause of the computer error that temporarily halted the June 13 Hubble Space Telescope science operations.
The payload computer problem, though has the telescope and science equipment in a safe and healthy state, was enough to suspend the famed science operation.
The Hubble science instruments were automatically placed in a safe configuration as the payload computer located in the Science Instrument Command and Data Handling unit, controls, coordinates and monitors the Hubble Science instruments.
Although tests to restart and reconfigure the computer and the backup were not successful, the information gathered in the process enabled the Hubble team to find out that the possible cause of the issue id in the Power Control Unit (PCU).
The PCU, which is located in the SI C&DH unit makes sure there is a constant voltage supply to the payload computer hardware, and has a regulator that provides at least five electricity volts to the payload computer and its memory. There is a secondary protection circuit sensing the level of the voltage leaving the power regulator and if the voltage goes below or exceeds the required level, this circuit notifies the payload computer and would hence stop operations.
The NASA team analysis presumed from this situation that it is either the level of the voltage from the regulator is not in the required levels, which might have tripped the secondary protection unit or the secondary protection circuit itself has over time degraded and stuck in the inhibit state.
As there were no ground commands available to rest the Power Control Unit (PCU), there would be a switch over to the SI C&DH backup side unit that houses the backup PCU. NASA would be given approval to proceed after testing procedures for the switch and associated reviews have been completed and thus the switch would begin today, Thursday, July 15 and if it becomes successful, it would still take some days before it totally returns to normal science operations.