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Hubble Space Telescope: Bugs found

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A defect in the voltage control caused the computer to fail

The Hubble space telescope has been out of order for a month due to a computer failure – now NASA has found out what the cause is. Accordingly, the defect is not, as initially assumed, in the payload computer responsible for the scientific instruments. Instead, the voltage control unit is responsible. Switching to the backup modules and the second control unit is still to take place today.

The Hubble Space Telescope has survived 31 years in space and has provided us with unique images and data during that time. But on June 13, 2021, it suddenly came to an end: The payload computer failed, the computer module that is responsible for controlling and coordinating the scientific instruments onboard the telescope. In response to this, the main computer put all instruments into “Safe-Mode”, an idle state for the purpose of security.

Since then, NASA has tried to find the cause of this failure. After several attempts to restart the payload computer had failed, the engineers first tried to switch to one of the three reserve memory modules, then the standard interface hardware was suspected – a component that enables communication with the central processor of the Payload computer guaranteed.

The tension control is to blame

After weeks of testing, NASA has finally found the fault: The computer failure is apparently not a component of the payload computer, but the Power Control Unit (PCU). This two-part module regulates the voltage supply to the computer and ensures that it is constant at five volts. If this is not the case, the control circuit issues a command that shuts down the computer.

In the current case, the analyzes indicate that the control unit either no longer supplies an acceptable voltage, or that the monitoring circuit is defective and incorrectly issues the switch-off command. The Power Control Unit is part of the “Science Instrument Command and Data Handling Hardware” (SI C&DH) – an ensemble of components that includes, in addition to the payload computer, other hardware, as NASA explains.

There is a backup

The good news: There is a backup. The SI C&DH module is redundant and all components are duplicated. Already once – in 2008 – NASA had to switch to the redundantly designed reserve module due to a defective hardware part. After the entire SI C&DH module was replaced during the service mission in 2009, a new backup is now available.

However, switching to the backup of this unit is more complicated than simply activating the replacement payload computer or the memory modules:

“The procedure is more complex and risky because to switch to the backup voltage regulator, several other hardware modules of the Telescope satellites are switched because they are linked to these modules,” explains NASA.

Switching takes place today

Today, July 15, 2021, this switch to the backup modules is to take place. “All test procedures for switching and the associated tests have been completed and NASA management has given us the green light,” says the statement. Since the same procedure was already carried out successfully in 2008, one is cautiously optimistic.

If the activation of the backup modules is successful and the switchover takes place, however, it will still take a few days before the Hubble space telescope can go back into operation, according to NASA.

Image Credit: NASA

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