Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/ops/swat/safing/08270/doxsey_update.txt Дата изменения: Mon Sep 29 14:54:22 2008 Дата индексирования: Sun Mar 2 03:07:57 2014 Кодировка: Поисковые слова: vallis

Date: Sun, 28 Sep 2008 18:31:24 -0400
From: Rodger Doxsey
Subject: HST safing last night


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.



Rodger Doxsey