Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/spst/lrpg/mission_planning/cycle_orbit_accounting/cycle13_S_orbit_accounting-final1.pdf Дата изменения: Fri Aug 20 21:22:37 2004 Дата индексирования: Sun Mar 2 12:57:04 2014 Кодировка: Поисковые слова: п п п п п п п

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

3700 San Martin Drive Baltimore, MD 21218 FAX (410) 338-4767

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. Issues related to a transition to Two-Gyro mode or the adequacy of the orbit allocation "tail" are not 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 (Table 2) Assumed HOPRs (2.5%) Remaining planned and anticipated orbits (Table 3) Subtotal orbits available for re-allocation: STIS --> non-STIS transfer Total available for re-allocation with STIS transfers: 80 orbits/wk +3520 +800 4320 -108 -2946 1266 -176 +/- 105 1090 +/- 105 85 orbits/wk +3740 +850 4590 -115 -2946 1529 -176 +/- 105 1353 +/- 105

Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration


2

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 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

3. Total Anticipated Orbits Remaining in Cycle 13:.
Table 3: Unexecuted/anticipated Orbits 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 This section details the remainder of Cycle 13. orbits which should be itly, those uncertainties Orbits 2300 123 126 38 40 93 226 176 +/- 105 3122 +/- 105 orbit totals which we know or which may need to be reserved for the A number of uncertainties exist in recommendations on the number of substituted for the loss of STIS fromthe Cycle 13 TAC runners-up. Explicare:

· 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. This number represents a best guess of the possible lower limit on the number that will be actually transferred. The uncertainty value is based on the fact that a decision is pending on 131 orbits of the Filippenko ToO program (10182) as well as other programs identified in Paul G.'s aperture and spectal element triage. · 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

4. STIS Orbits Lost

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. Note that this number is comparable to the number of orbits computed available in the summary section based upon the higher execution rate.