The Hubble Space Telescope has been offline for a week because of a bug in its payload computer, and it might take longer than we expected to get it back online. NASA reports it has tried several times to switch to backup memory modules, but it hasn’t worked. Team members are now examining the possibility that the issue is more severe, but we won’t know the extent of the damage until the investigation is complete.
The problem began when the payload computer for the telescope suddenly stopped working on June 13th. This is a different system from Hubble’s main computer that manages the science instruments. It pings the main computer with a “keep alive” signal, but that ceased on June 13th. This sent the observatory into safe mode, where it has remained ever since.
At first, NASA thought the problem was caused by a deteriorating 64K memory module. Yes, that is a very small amount of active memory for 2021, but this is a NASA Standard Spacecraft Computer-1 (NSSC-1) system from the 1980s. Fortunately, four redundant memory modules are built into the NSSC-1. NASA should have been able to switch the computer to a backup, and everything should have been fine. Despite this, the system stubbornly refuses to cooperate.
NASA now believes the system failure lies elsewhere in Hubble’s hardware, and the memory corruption was merely a symptom. The focus now is on the Standard Interface (STINT) hardware, which connects the Central Processing Module (CPM) to the computer’s other components. The team is designing tests that can be run remotely to diagnose the problem.
Luckily, there is still hope even if NASA determines the payload computer is busted. During Hubble’s last servicing mission in 2009, astronauts replaced a recently failed Science Instrument Command and Data Handling unit, which contains the payload computer and a backup for that system. NASA has reviewed the procedure for swapping to the backup payload computer, which accesses the same four memory modules as the current one.
So, as long as the backup computer and at least one memory module are still functional, Hubble should be alive again soon. If, however, there’s a problem with the backups, this could be the telescope’s swansong. That would leave the world’s astronomers without a high-power orbiting observatory until NASA’s long-delayed Webb telescope launches (hopefully) late this year.