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

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

Rodger Doxsey, Duccio Machetto, Dave Soderblom Denise Taylor, Bill Workman, Ian Jordan February 24, 2004 Cycle 13 Projections and TAC Orbit Allocation Recommendations

1. TAC Orbit Limit Recommendation Summary for Cycle 13
This memo presents the recommendation of the Long Range Planning Group for the number of HST orbits that should be made available to the Cycle 13 TAC for allocation to the GO community. The recommendation is based on the following considerations:
· · · · Net orbits available for Cycle 13 programs after taking into account the current cycle's execution status. Deductions from the net available orbits based on preallocated Cycle 13 orbits. Additions to the net available orbits to account for uncertainties in the Cycle 13 orbit execution. The nominal Cycle 13 LRP runs from July 1, 2004 to June 30, 2005 (2004.183 - 2004.182).

Supporting data is provided on the following pages. Table 1: Recommedation for Cycle 13 TAC Orbit Allocation Recommendation Considerations Net available orbits for Cycle 13 programs Deductions from net available orbits: Credits to net available orbits (oversubscription required to maintain observatory efficiency:) Total available for TAC orbit allocation: Orbits 3600 -1285 +800 3115

Table 2: Recommended Limit on MAMA/SBC Observations Recommended combined MAMA/SBC limit 1080 orbits

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2. Net Number of Orbits Available for Cycle 13
This is computed by determining the net number of weeks available to execute Cycle 13 orbits within the nominal Cycle 13 boundaries, and multiplying that number by the current orbit execution rate. The net number of weeks available is computed by determining the absolute minimum number of weeks necessary to complete the remaining unexecuted Cycle 12 orbits and subtracting that from the actual weeks remaining in the current cycle. This number is then subtracted from the nominal Cycle 13 duration (ie. - 52 weeks). Table 3: Summary of Remaining Current Cycle Visits as of 2004.061 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 (2.5%): Subtotal: Orbits 1770 69 20 140 50 2049

Table 4: Weeks available within Cycle 13 Boundary ( < 2005.182) 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 13 weeks needed to complete current cycle (Weeks to execute - weeks remaining in current cycle) Net number of weeks for Cycle 13 orbits = (52 - weeks needed for current cycle) 26 19 7 45

Table 5: Net Orbits Available within Cycle 13 Boundary Net number of orbits available for Cycle 13: (Net weeks * current orbits/week = 45 * 80) 3600 orbits


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3. Deductions from Net Available Cycle 13 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 12 (with various assumptions) Calibration orbits (~8% of net available from Table 5) HOPR (2.5% of net available from Table 5) DD
a

250 90 100 100 520 185 40 1285 orbits

Chandra allocated orbits Multi-cycle proposals GTO proposals 2-Gyro On-orbit Test Support subtotal
a. Director's formula of (2yrs DD@300/yr - 400orbsUDF)/(2years)

4. Additions to Net Available Cycle 13 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 13 interval. In fact a normal Cycle will have observations whose constraints force them to be scheduled 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. Based on the results of the actual Cycle 12 TAC allocation and scheduling results to date, we recommend planning on 10 weeks worth of oversubscription in Cycle 13. . 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 13: (Net additional weeks* current orbits/week ) 10 80 800


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5. SAA-Free Allocation Limit:
Based on the instrument complement and the potential for a subscription of highly constrained programs , HST orbits that are not impacted by the SAA will be in high demand again in Cycle 13. 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 orbits that can be allocated to observations that use the STIS/MAMA and ACS/SBC. LRPG has determined from experience that the the LRP is viable if the number of these observations is limited to 24 orbits per week on average. Table 8 provides the calculation of the recommended limit on the combination of STIS/MAMA and ACS/SBC observations. Table 8: SAA Free Orbit Allocation Limits net number of weeks available for Cycle13 Max number of STIS/MAMA and ACS/SBC orbits per week: Recommended combined MAMA/SBC limit 45 24 1080 orbits

6. SNAP Allocation Limit:
Analysis of the SNAP program subscription is in progress and recommendations for Cycle 13 will be reported in a subsequent memo.