Last night, the NSSC-I, and all the Instruments, were placed into safemode by the 486 (spacecraft) computer. The analysis has been hampered a bit by the fact that the safing took place when the telescope was out of communication with the ground, and more so by the fact that whatever went wrong has prevented downloading the NSSC-I memory, which would have a detailed record of the events stored in it. At this point, it seems the problem is in the hardware located in a unit called the CU/SDF (Command unit/Science data formatter I believe). This unit is associated with the NSSC-I, and handles commands and telemetry functions between the NSSC-I and the instruments and the 486. It appears that the problem is localized to processes that collect some of the telemetry data from the CU/SDF itself. So far, there is no sign that any commands have been corrupted.
The NSSC-I, the CU/SDF, and other associated electronics have had no failures since launch in 1990. We have been running on the A-Side of the electronics. There is a B-side that we can now switch to (but has been off for the last 18 years). The process for doing this is quite complicated, but was worked out in detail several years ago in anticipation of a problem some day. The detailed scripts for the switch over will be retested against the VEST tomorrow. The VEST is an identical replica of the computer, data, and other electronic systems on Hubble. If this test goes smoothly, then we are likely to carry out the transfer on Thursday of Friday. After that, the instruments would be recovered from safemode.
There are two JISs (Joint Integrated Simulations, training sessions for JSC, GSFC, and STScI for SM4) scheduled for Monday and Tuesday. These will proceed as planned. In parallel with the JISs and the test in the VEST, a group of the engineers at GSFC must go through the planned commanding for SM4 and determine which procedures and commanding must be changed for SM4, if we are running HST on the B-side rather than the planned A-side. Any changes to the SM4 commanding will also have to be tested with the VEST facility prior to SM4. The assessment of how much work is involved is likely to be completed by the end of the day on Wednesday. If it is extensive, it has the potential for delaying SM4 a few days.
There is a spare SIC&DH (which is the name for the conglomeration of the NSSC-I, CU/SDF, and other acronyms and hardware) on the ground. It is a fairly large unit that mounts on the inside of one of the electronics bays. There is no way it could be made ready for flight by the planned October SM4 launch date. The HSTP engineers and management are actively looking at how much time would be required to get it certified and ready for flight, build the carrier to store it in the Shuttle bay, and train the crew on EVA procedures for it. I should emphasize that no decision has been taken about replacement of the unit in SM4, only the work necessary to figure out what the impact would be.
We will keep you updated through the week, as work on this problem proceeds. Meanwhile, the telescope is continuing to do a bit of science. Astrometry observations do not require Instruments or the NSSC-I, so they are proceeding.
