The Hubble space telescope, launched in 1990, has four memory modules alongside the payload computer that controls the scientific instruments. Last week the computer, a NASA Standard Spacecraft Computer-1 (NSSC-1) system built in the 1980s, stopped operating and couldn’t be restarted.
Initial indications pointed to a degrading computer memory module as the source of the computer halt. When the operations team attempted to switch to a back-up memory module, however, the command to initiate the backup module failed to complete. Another attempt was conducted on both modules Thursday evening to obtain more diagnostic information while again trying to bring those memory modules online. However, those attempts were not successful.
The payload computer was originally designed with 1700 diode-transistor logic (DTL) circuits manufactured by Fairchild Semiconductor for both the CPU and the I/O modules as the owest power bipolar logic devices available in the late 1970s. The hardware included four memory modules of 4K words each to provide redundancy with both plated wire and magnetic core memory technologies being used.
The computer is on the Science Instrument Command and Data Handling unit and is used to control and coordinate the science instruments and monitor them for health and safety purposes. It is fully redundant with a second computer that can be switched over to in the event of a problem. Both computers can access and use any of four independent memory modules, which each contain 64K of CMOS memory devices. The payload computer uses only one memory module operationally at a time, with the other three serving as backups.
One of these modules appears to have degraded but switching to a backup module also failed.
The operations team will be running tests and collecting more information on the system to further isolate the problem. The science instruments will remain in a safe mode state until the issue is resolved and the telescope itself and science instruments remain in good health.
After 30 years in operation, Hubble has been set to be replaced by the James Webb Space Telescope, a joint development by NASA and the European Space Agency (ESA). This is currently schedule to launch on 31 October 2021 but problems with the Ariane rocket may push that back into December or January 2022.
Electric car maker Tesla recently saw a problem with the lifetime of its flash memory module in certain models, prompting a recall.
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