NASA continues to diagnose a problem with the Hubble Space Telescope’s payload computer after completing another series of tests on June 23 and 24. The payload computer was stopped on June 13 and the spacecraft stopped collecting scientific data. The telescope itself and its scientific instruments remain in good condition and are currently in a safe configuration.

The spacecraft has two payload computers, one of which serves as a backup, located on the Science Instrument and Command and Data Handling (SI C&DH) unit. There are several pieces of hardware that make up both payload computers including, but not limited to:

  • a Central Processing Module (CPM) that processes the commands that coordinate and control the scientific instruments
  • a standard interface (STINT) that bridges communication between the computer’s CPM and other components
  • a communication bus that contains lines that carry signals and data between hardware
  • and an active memory module that stores operational commands to the instruments. There are three additional modules that serve as a backup.

Further tests conducted on June 23 and 24 included turning on the backup computer for the first time in space. The tests showed that numerous combinations of these pieces of hardware from both the primary and backup payload computers all had the same error – commands to write to or read from memory were unsuccessful.

Since it is very unlikely that all individual hardware elements will have a problem, the team now sees other hardware as possible culprits, including the Command Unit / Science Data Formatter (CU / SDF), another module on the SI C&DH. The CU formats and sends commands and data to specific destinations, including scientific instruments. The SDF formats the scientific data from the scientific instruments for transmission to the ground. The team also examines the power regulator to see if the voltages being supplied to the hardware may not be what they should be. A power regulator ensures a constant voltage supply. If the voltage is outside the acceptable range, the problems observed may arise.

For the next week, the team will continue to evaluate the SI C&D unit hardware to see if something else could be causing the problem. If the team determines that the CU / SDF or the power regulator is the likely cause, they will recommend switching to the backup CU / SDF module and the backup power regulator.


Hubble was founded in 1990 and has been watching the universe for over 31 years. It has contributed to some of the most significant discoveries of our cosmos, including the accelerated expansion of the universe, the evolution of galaxies over time, and the first atmospheric studies of planets outside our solar system. Read about some of Hubble’s key scientific contributions.

https: //www.NASA.Government/Feature/God/2021 /Operations-ongoing-to-recovery-payload-computer-on-nasas-hubble-space-telescope


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