[NASA] Operations Continue to Restore Payload Computer on NASA's Hubble Space Telescope
NASA continues to work on resolving an issue with the payload computer on the Hubble Space Telescope. 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. The telescope itself and science instruments remain in good health.
The computer halted on Sunday, June 13. An attempt to restart the computer failed on Monday, June 14. 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 is a NASA Standard Spacecraft Computer-1 (NSSC-1) system built in the 1980s that is located on the Science Instrument Command and Data Handling unit. The computer’s purpose is to control and coordinate the science instruments and monitor them for health and safety purposes. It is fully redundant in that a second computer, along with its associated hardware, exists on orbit 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 Complementary Metal-Oxide Semiconductor (CMOS) memory. The payload computer uses only one memory module operationally at a time, with the other three serving as backups.
Launched in 1990, Hubble has contributed greatly to our understanding of the universe over the past 30 years.
The NASA Standard Spacecraft Computer-1 (NSSC-1) is a computer developed as a standard component for the MultiMission Modular Spacecraft at the Goddard Space Flight Center (GSFC) in 1974. The basic spacecraft was built of standardized components and modules, for cost reduction. The computer had 18 bits of core memory or plated wire memory; up to 64 k. 18 bits was chosen because it gave more accuracy (x4) for data over a 16 bit machine. Floating point was not supported.
The NSSC-1 had an assembler/loader/simulator toolset hosted on Xerox XDS 930 (24- bit) mainframe. An associated simulator ran at 1/1000 of real time. The Xerox computer was interfaced to a breadboard OBP in a rack. (Which, of course, operated at room temperature ambient conditions). Later, the Software Development and Validation Facility (SDVF) added a flight dynamics simulator hosted on a PDP-11/70 minicomputer.[2]
A purpose-built NSSC-1 Flight Executive was developed and used on the Solar Maximum Mission (SMM) and subsequent flights. It time sliced tasks at 25 ms. It included a stored command processor that handled both absolute time and relative time commands. It included a status buffer that could be telemetered back to the ground. It required a lot of memory, typically more than half of that available, leaving the rest for applications and spare.[3]
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