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SPACE
TELESCOPE
SCIENCE
INSTITUTE
MEMORANDUM
TO:
FROM:
DATE:
SUBJECT:
Rodger Doxsey, Dave Soderblom, Denise Taylor (HD)
Ian Jordan (OPT/LRPG)
September 5, 2001
LRP Impact of the STIS Side 1 Electronics Safing
This memo outlines the estimated impact of the STIS safing on the HST long range plan (LRP). A
number of significant effects on HST execution rate have been identified, with an overall impact
resulting in reduced execution rates through the end-of-Cycle, and stretching of the Cycle-end
time for SAA-free orbits by 1.5-2.5 months.
• Approximately 11 weeks (61-82 days) of STIS observing time was directly lost or delayed as a
result of the safing. [q.v. table, next page]
• During the 2001.134 week, 54 orbits of STIS were scheduled, only 12 completed successfully.
• During the “full” 25 weeks of STIS observing this year, the mean prime observing rate has been
43 STIS orbits/week. Here, “full” includes the 3 other safing events on January 3, March 5, and
April 28, but not the 11 weeks of STIS downtime.
The STIS down-time produces three major effects on the Cycle-end date. The factors are not independent and do not produce a purely additive effect.
• During the flight calendar weeks of 2001.141-211, only 62.3 prime orbits/week were scheduled-down 16 orbits/week. The effect of this reduction is to stretch the cycle by about 2.3 weeks-not considering other effects of the safing.
• A total of 297 orbits of prime non-STIS was executed above the expected 24.25 orbits/week
during the STIS-down-time. Many of these were future SAA-hiders executing in SAA-free
orbits. The remainder of the Cycle has become relatively “WFPC-depleted” and will likely
result in a slightly reduced mean execution rate due to depletion of SAA-hiders, perhaps by 3-6
orbits/week.
• The nominal “Large STIS visit” (3+ orbit-sized visits) execution rate is 7.9 visits/week (4.35 of
which are MAMAs). Generally, large visits require SAA-free time, and 11 such weeks were
lost. The SAA-free end-of-cycle will be delayed anywhere between 5 & 8 weeks. This is less
than the STIS down-time since some later-planned non-STIS SAA-free visits executed during
the 11 weeks.
Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration
2
Other impacts include replanning activities and proposal reprocessing for visits impacted by the
STIS downtime. Replanning activities include moving Cycle 10 visits later to accommodate Cycle
9 visits moved earlier into the plan. A “bow wave” effect on large-orbit visits in the LRP has
already been noticed.
Table 1: Major Events in the 2001 STIS Side 1 Electronics Safing
Days from
Safing
Event
Date/Time
STIS Safing
2001.136:05
-
First STIS exposure (CCD anneal)
2001.192:02
~56
First STIS external (CCD parallel)
2001.194:05
~58
First STIS external Prime GO
2001.197:00
~61
First STIS/MAMA Prime external GO
2001.205:01
~69
Enabling of STIS Imaging & Wide-slit spectroscopy
2001:211
~75
Enabling of All STIS science
2001:218
~82