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SP CE A TELESCOPE SCIENCE INSTITUTE
MEMORANDUM
TO TO: FROM: DATE: SUBJECT:

3700 San Martin Drive Baltimore, MD 21218 (410) 338-5037 & 4806 FAX (410) 338-4767

Rodger Doxsey, Dave Soderblom, Denise Taylor I. Jordan, A. Vick, B. Workman January 23, 2003 Cycle 12 Projections and TAC Orbit Allocation Recommendations

1. TAC Orbit Limit Recommendation Summary for Cycle 12
This memo presents the recommendation of the Long Range Plan Group for the number of HST orbits that should be made available to the Cycle 12 TAC for allocation to the GO community. The recommendation is based on the following considerations:
· · · · Net orbits available for Cycle 12 programs after taking into account the current cycle's execution status. Deductions from the net available orbits based on preallocated Cycle 12 orbits Additions to the net available orbits to account for uncertainties in the Cycle 12 orbit execution. Cycle 12 runs from July 1, 2003 to June 30, 2004 (2003.182 - 2004.181)

Supporting data is provided on the following pages. Table 1: Recommedation for Cycle 12 TAC Orbit Allocation Recommendation Considerations Net Orbits available for Cycle 12 programs Deductions from net available: Credits to available orbits Total available for TAC orbit allocation: Orbits 3760 -1449 +640 2951

Table 2: Recommended Limit on MAMA/SBC Observations Recommended combined MAMA/SBC limit 1128 orbits

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2. Net Orbits Available for Cycle 12
This is computed by determining the net number of weeks available to execute Cycle 12 orbits within the nominal Cycle 12 boundaries, and multiplying that number by the current orbit execution rate. The net number of weeks available is computed by determining the minimum number of weeks necessary to complete the remaining current cycle orbits and subtracting that from the actual weeks remaining in the current cycle. This number is then subtracted from the nominal Cycle 12 duration (ie. - 52 weeks). Table 3: Summary of Remaining Current Cycle Visits as of 2003.034 Current Cycle Proposal Types Currently having plan windows Current Cycle (non-DD, non-ToO) without Plan Windows: Expected Current Cycle DD to be executed Expected Current Cycle ToO to be executed: HOPR orbits for above orbit pool (2%): Subtotal: a. based on current ToO execution rate of 4.3 orbits/week Table 4: Weeks available within Cycle 12 Boundary ( < 2004.181) Current execution rate = 80 orbits/week Minimum weeks required to execute current cycle = (Table 3 subtotal/execution rate) Weeks remaining in current cycle Minimum number of Cycle 12 weeks needed to complete current cycle (Weeks to execute - weeks remaining in current cycle) Net number of weeks for Cycle 12 orbits = (52 - weeks needed for current cycle) 29 24 5 47
a

Orbits 1885 126 80 180 45 2286

Table 5: Net Orbits Available within Cycle 12 Boundary Net number of orbits available for Cycle 12: (Net weeks * current orbits/week = 47 * 80) 3760 orbits


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3. Deductions from Net Available Cycle 12 Orbits:
Of the total number of orbits available in a cycle, some are reserved for calibrations, director's discretionary time, HOPRs, GTOs, and continuing multi-cycle proposals. The following table summarizes these "pre-allocated" orbits. The summary preserves the different assumptions on chosen cycle end date and the uncertainty in execution rate. Table 6: Pre-Allocated/Reserved From Cycle 11 (with various assumptions) Calibration orbits (10% of net available from Table 5) HOPR (2% of net available from Table 5) DD - Ultra Deep Field Other DDa Chandra allocated orbits Multi-cycle proposals GTO proposals subtotal
a. Director's formula of (2yrs DD@300/yr - 400orbsUDF)/(2years)

376 75 400 100 100 213 185 1449 orbits

4. Additions to Net Available Cycle 12 Orbits:
The orbit calculations to this point are based on an assumption that the programs accepted by the TAC will have observing windows that are evenly distributed across the nominal Cycle 12 interval. In fact a normal Cycle will have observations whose constraints up to 6 months or more beyond the end of the cycle. Therefore we must estimate how many orbits will schedule beyond the nominal end of the cycle, and adjust the recommended TAC allocation by that amount. Number of Cycle 11 orbits expected to schedule beyond nominal cycle end time = 500 (~ the number expiring beyond 2003.181) to 650 (including a fraction of unschedulables, HOPRs and as-yet unsubmitted DDs). This is approximately 8 weeks of HST observations (at 80 orbits/week). This is the component of the `tail' in the LRP. Table 7: `Tail' Required to Maintain Execution Rate over Cycle 12-13 Transition Extra weeks required to maintain level telescope subscription: (within nominal cycle boundary, based on operational history) Average number of est_orbits per week Net Additional orbits available for Cycle 12: (Net additional weeks* current orbits/week ) 8 80 640


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5. SAA-Free Allocation Limit:
Based on the instrument complement for Cycle 12, HST orbits that are not impacted by the SAA will continue to be in high demand. The TAC should be aware that there is an absolute limit in the number of SAA-free orbits in a nominal 52 week cycle and these orbits must be shared with all instruments. Observations that use the STIS/MAMA and ACS/SBC must be scheduled in orbits that are not SAA impacted. Observations that use other instruments and modes may also be constrained to SAA-free orbits for various reasons. This fact by definition sets a limit on the number of of orbits that can be allocated to observations that use the STIS/MAMA and ACS/SBC . Table 2 provides recommended limits on the combination of STIS/MAMA and ACS/SBC observations. Table 8 provides the calculation of it. Table 8: SAA Free Orbit Allocation Limits net number of weeks available for Cycle12 Max number of STIS/MAMA and ACS/SBC orbits per week: Recommended combined MAMA/SBC limit 47 24 1128 orbits