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From: gsh7w@astsun.astro.Virginia.EDU (Greg Hennessy)
Newsgroups: sci.astro,sci.space,sci.space.shuttle
Subject: ASTRO status at 4/16:00 MET
Message-ID: <1990Dec6.230645.27668@murdoch.acc.Virginia.EDU>
Date: 6 Dec 90 23:06:45 GMT
Sender: news@murdoch.acc.Virginia.EDU
Organization: University of Virginia
Lines: 49

Well, the last 24 hours has brought good news, extremely bad news, and
now decent news. The good news was that during shift nine, the first
11 objects observed averaged 76 percent of the scheduled observing
time, a value that made the science teams VERY happy. Most of the
tracking was done by the astronauts by joystick, and obtained lots of
data for the spectrometers. The patch to the star tracker did not
clear the problem, but the automatic tracking was tried only three
time, suceeding once, the first time it did suceed. The stability was
excellent, and there was hope that the star trackers could be made to
work before very long. Even the manual guiding gave respectable images
for the UIT, which is most affected by loss of the star trackers.
Observations were done of M100, M74, Hercules X-1, the Cygnus Loop,
Alpha Hydra, the Vela SuperNova Remnant, and M82, among others. Then
disaster struck.

The second Data Display Unit (DDU) failed. This left the astronauts
with no way to enter commands to the instruments. This meant that the
UV instruments could not take any data whatsoever,  even though BBXRT
was unaffected. The day was understandable hectic, but a contingency
plan has been developed. All the UV instruments have a backup ground
based controls. During the past shift these instrumetns were powered
up and tested. During this time the shuttle gave priority to BBXRT
telescopes. Starting with shift 11, the data for the telescopes will
be entered on teh ground, and uploaded. The astronauts will still do
the manual guiding, but otherwise the UV instruments will be
controlled on the ground. The science observations for shift 11 were
canceled, and a system was iinstutued to first try to get UIT working,
then HUT, then WUPPE. This was in order of decreasing  field of view,
or of increasing difficulty. This scenerio was never simulated, since
loss of both DDU's was thought to be an unreasonable scenerio. UIT
will pick two targets on opposite sides of the sky, NGC 1399 at Ra 3
hours 36 min and Centaurus A at Ra 13 hours 22 min. UIT will
"ping-pong" back and forth between these two targets for 4 orbits,
then HUT will try 2 orbits trying to acquire the quasar Q1821, then
WUPPE will try 2 orbits trying to acquire GAM-GEM. On shift 12 other
targets will be tried, or increasing scientific interest and degree of
difficulty. These targets are still being worked out. Once confidence
is gained in this mode of observing, secondary observations will be
allowed. 

It now appears that a 10'th day of the mission is possible.

Boy, was today hectic.

--
-Greg Hennessy, University of Virginia
 USPS Mail:     Astronomy Department, Charlottesville, VA 22903-2475 USA
 Internet:      gsh7w@virginia.edu  
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