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SPACE
TELESCOPE
SCIENCE
INSTITUTE
MEMORANDUM
TO:
FROM:
DATE:
SUBJECT:
Rodger Doxsey, Duccio Machetto, Robert Williams
Bill Workman, Denise Taylor, Ian Jordan
September 3, 2004
Orbit allocation recommendation for Cycle 13 supplemental programs.
1. Supplementary Orbit Recommendation Summary
This document summarizes our meeting on this date to review the orbit allocation requirements
for maintaining HST scheduling efficiency following the loss of STIS observing on August 3,
2004. The recommendation given here represents the minimum number of supplemental orbits
required through the remainder of Cycle 13. Allocation of more than this amount is acceptable but
it will extend the agreed upon 6 week ‘tail’. This extension will need to be offset by an equivalent
deduction from the Cycle 14 TAC allocation.
Table 1: Summary Recommendation for post-STIS TAC Orbit Allocation
Total orbits available until C13/C14 boundary (44 weeks)
3740
HOPR allocation (2.5%)
-115
Remaining planned and anticipated orbits (Table 3)
-2795
Subtotal orbits available for allocation:
830
* STIS --> non-STIS transfer
-180
Subtotal with STIS --> non-STIS Transfer:
650
** “Tail” to maintain efficiency (6 weeks)
+500
Minimum total number of orbits required to be allocated:
1150
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Notes for Table #1:
* This value is the approximate minimum number of orbits from current unexecuted STIS observations that are expected to be converted to use non-STIS instruments.
** The “tail” is added to allow smooth and efficient transition between Cycle 13 and Cycle 14 and
to adjust for the inability to schedule all visits within the nominal Cycle 13 boundary due to constraints on some programs. The recommended tail value is included in Table #1.
2. Total remaining orbits available for execution in Cycle 13.
The total number of orbits which remain available for execution is based upon the number of
weeks remaining to be scheduled in the Cycle. The execution rate is projected to increase from the
historical rate with STIS observations to as much as 85 orbits per week without STIS observations. We have chosen to use the maximum expected rate in these calculations to ensure that
enough observations are allocated.
Table 2: Weeks available within Cycle 13 Boundary ( < 2005.185)
Weeks remaining in current cycle as of August 18, 2004
(44 weeks)
80 est_orbits/
wk
85 est_orbits/
wk
3520
3740
3. Total Anticipated Orbits Remaining in Cycle 13:.
Table 3: Unexecuted/anticipated Orbits
Type
Orbits
Planned (with plan windows)
2150
Unplanned (without plan windows)
123
Calibration orbits (Phase 2s not in)
126
non-STIS Chandra allocated orbits (Phase 2s not in)
38
Engineering (2-Gyro Tests)
40
Directors Discretionary (100 orbits minus 7 orbits in-house)
93
Target of Opportunities
225
subtotal
2795
This section details the orbit totals which we know or which may need to be reserved for the
remainder of Cycle 13. A number of uncertainties exist in recommendations on the number of
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orbits which should be substituted for the loss of STIS from the Cycle 13 TAC runners-up. Explicitly, those uncertainties are:
• The exact HST est_orbit execution rate without STIS is unknown but is expected to be higher than the
‘with-STIS’ rates.
• Target of Opportunity activations are uncertain. We assumed that all activations in the PANS ToO program will be used (10339 & 10340) and a significant fraction of the remaining non-STIS ToOs will be used
(60%-100% of remainder used).
• There are approximate 280 STIS orbits that may be transferrable to other instruments. This number
includes ~ 40 orbits identified in Paul G.’s aperture and spectal element triage and 131 orbits of the Filippenko ToO program (10182). Both of these are likely to be converted. We have assumed that ~50% of the
remaining orbits will be converted as well. Final values are pending PI proposals and TTRB decisions.
• DD allocation rate may change in a post-STIS environment. We assume here that all of the remainder of
the original allocation will be used.
4. Lost STIS Orbits
Approximately 1270 orbits of prime STIS GO visits will be lost, plus 224 orbits of unexecuted
STIS Target of Opportunity visits, for an approximate total of 1494 orbits. The net number lost is
approximately 1314 after subtracting the number of orbits that will be recovered by converting the
observations from STIS to a non-STIS instrument.