Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/spst/lrpg/mission_planning/cycle_orbit_accounting/cycle13_S_orbit_accounting.pdf Дата изменения: Fri Aug 20 02:31:07 2004 Дата индексирования: Sun Mar 2 12:49:40 2014 Кодировка: Поисковые слова: tail

SP CE A TELESCOPE SCIENCE INSTITUTE
MEMORANDUM
TO TO: FROM: DATE: SUBJECT: Rodger Doxsey, Denise Taylor, Bill Workman, Ian Jordan August 18, 2004 HST orbit availability after the STIS Suspend

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1. Supplementary Orbit Recommendation Summary
Following the STIS suspend on August 3, 2004, the anticipated unavailability of STIS in the remainder of Cycle 13 implies a dearth of orbits in the remainder of the Cycle 13 HST long range plan. This document provides an accounting of the orbits allocated to HST and an updated estimate of the number of orbits which would need to be filled by supplementary means. No discussion of ancillary issues, such as transition to Two-Gyro mode and adequacy of the tail, is discussed in this memo. Table 1: Summary Recommedation for post-STIS TAC Orbit Re-Allocation Recommendation Considerations Total est_orbits until C13/C14 boundary (44 weeks) "Tail" to maintain efficiency (10 weeks) Subtotal orbits to plan for Assumed HOPRs (2.5%) Remaining "In house" orbits Total available for re-allocation: 80 orbits/wk +3520 +800 4320 -108 -3158 +/- 90 1054 +/- 90 85 orbits/wk +3740 +850 4590 -115 -3158 +/- 90 1317 +/- 90

2. Total Orbits to Plan for in the Remainder of Cycle 13.

The total number of orbits which remain to be planned for is based upon the number of weeks

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which are planned to be filled. A "tail" is used to allow smooth and efficient transition between Cycles and adjust for inability to schedule all visits within Cycle boundaries due to constraints on some programs. The tail used here is the same tail length specified in the February 24 pre-TAC ODM orbit recommendation memo. Two different conceivable execution rates are specified.

Table 2: Weeks available within Cycle 13 Boundary ( < 2005.185) 80 est_orbits/ wk Weeks remaining in current cycle (44 weeks) "Tail" weeks at end of cycle (10 weeks): Subtotal 3520 800 4320 85 est_orbits/ wk 3740 850 4590

3. Total Reserved Orbits Remaining in Cycle 13:
This section details the orbit totals which have already been reserved for all known commitments.. Table 3: Pre-Allocated/Reserved From Cycle 12 Type Planned (with plan windows) Unplanned (without plan windows) Calibration orbits (Phase 2s not in) non-STIS Chandra allocated orbits (Phase 2s not in) Engineering (2-Gyro Tests) Directors Discretionary (100 orbits minus 7 orbits in-house) Target of Opportunities STIS --> non-STIS transfer subtotal Orbits 2300 123 126 38 40 93 328 +/- 50 110 +/- 40 3158 +/- 90

A number of uncertainties exist in recommendations on the number of orbits which should be substituted for the loss of STIS fromthe Cycle 13 TAC runners-up. Explicitly, those uncertainties are:


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HST est_orbit execution rate may or may not increase with the loss of STIS. Target of Opportunity activations are uncertain. Number of STIS orbits transferrable to other instruments has not been finalized. DD allocation rate may change in a post-STIS environment.

This document assumes that all DD time PANS ToO program will be used (10339 non-STIS ToOs will be used (60%-100% of STIS-to-non-STIS transfers is loosely

will be used. Also assumed is that all activations in the & 10340) and a significant fraction of the remaining of remainder used). A guestimate range for the number based on a triage performed by the STIS team.

4. STIS Orbits Lost

Approximately 1286 orbits of STIS visits with plan windows will be lost, and another 34 orbits of unplanned STIS (not including Target of Opportunity visits), for an approximate total of 1320 orbits. Note that this number is comparable to the number of orbits computed available in the summary section based upon the higher execution rate.