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Technical Resource Allocations

Detailed resource allocation plan for the Lunar Reconnaissance Orbiter mission, including mass, fuel, and power allocations. Derives fuel mass allocation from dV budget, spacecraft dry mass, and subsystem components allocation.

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Technical Resource Allocations

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  1. Technical Resource Allocations Michael Pryzby

  2. Technical Resource AllocationsFlight Dynamics Delta V Propellant

  3. dV/Fuel Mass Allocation • Assumes 1480 kg wet launch mass • MRD-24: The launch vehicle must be capable of delivering a 1480 kg payload to a trajectory with a C3 > -1.85 • Given dV budget, determine fuel mass assuming maximum wet mass at liftoff • Derives allocation for spacecraft dry mass • dV budget determined by analysis & lunar mission experience • MCC1 allocation is 3-sigma, could be improved by performing maneuver earlier than 24 hours but holding worst case • MRD-25: TLI accuracy at orbiter sparation from the LV third stage shall be within +/- 3 m/sec (TBR) (3-sigma) of target inertial velocity. • FDS 2.3.1: LRO shall perform an MCC1 maneuver at L+24 (TBD) hours to correct for LV dispersions. • LOI allocation is deterministic, detailed analysis exists to support, all physics not a function of perturbations • Stationkeeping is deterministic, detailed analysis exists to support, actual dV cost is only 150 m/sec, may move extra 30 m/s to margin • MRD-12: The primary mission shall be conducted in a circular mapping orbit with a nominal mean altitude of 50 +/- 20 km (altitude is measured to mean lunar surface). • Extended mission is place holder only, allows many options for unknown extended mission, could be used for contingency in mission orbit if needed • MRD-22: LRO shall carry sufficient consumables to allow for a four year extended mission in a low maintenance orbit. • Margin is 20 m/s • LOI and extended mission dV should not be used to calculate dV percent margin • 8% dV margin on MCC1 and SK dV budgets (22% if 30 m/s moved from SK to margin)

  4. Mission Phase LRO Baseline dV (m/sec) Fuel Mass (kg)  Comments  MCC 75 52 3s, MCC @ L+24 hours Lunar Insertion – 1st burn 391 210 1st insertion burn, finite dV, any launch date, 20% off-pulsing Lunar Insertion – All other burns 535 288 All other insertion burns, finite dV Station-keeping 180 77 +/- 20 km altitude, 3s including errors Extended Mission 125 48 Placeholder only Margin 20 8 Momentum Unloading 16 Other 14 De-spin, Residuals, Pressurant Total 1326 713 dV/Fuel Mass Allocation * Assumes 1480 kg launch wet mass

  5. Technical Resource AllocationsMass Consumables Spacecraft Wet Mass Spacecraft Dry Mass

  6. Mass • Technical Resource Allocations Document, 431-SPEC-000112 • Mass allocations budges include: • Spacecraft Allocation – Wet • Spacecraft Allocation - Dry • Wet Mass Allocation (Consumables) • Allocation Derivations: • Spacecraft Wet Mass Allocation • MRD-1: The max allowable spacecraft mass – 1480 kg • MRD-24: The launch vehicle must be capable of delivering a 1480 kg payload to a trajectory with a C3 > -1.85 • Wet Mass Allocation • Derived from dV / Fuel Mass Allocation • Spacecraft Dry Mass Allocations • Derived from Current Best Estimates • Contingency based upon Design Maturity Factor

  7. Subsystem Components Allocation  Comments  SubSystem Mass (kg) Consumables 715.30 Propellant 713.0 Derived from Delta V budget - includes 3s Pressurant 2.3 Wet Mass Allocation - Consumables Table 3‑2 - Spacecraft Wet Mass Allocation - Consumables

  8. Subsystem Components Allocation  Comments SubSystem Mass (kg) L/V Wet Mass Capability 1480.00 MRD Req’t: 1.2.10 Derived Wet Mass Allocation 715.30 Propellant Budget derived from Delta V budget Max Dry Mass Allocation 764.70 Remaining mass Spacecraft Mass Allocation - Wet  Table 3‑1 - Spacecraft Mass Allocation - Wet Table 3‑2 - Spacecraft Wet Mass Allocation

  9. Subsystem Components Allocation  Comments SubSystem Mass (kg) Total Dry Mass 710.3 Concept J Spin balance Weight 25.0 Place holder S/C Bus Subtotal 595.5 Mechanical 155.1 Mechanisms 52.8 Thermal 32.4 Power 76.2 ACS 63.4 PDE 16.8 Propulsion (Dry Mass) 105.8 C&DH 19.5 S Comm 12.6 Ka Comm 18.5 Electrical 40.0 Instruments Subtotal 89.9 CRaTER 6.4 Diviner 11.9 LAMP 5.3 LEND 23.2 LOLA 15.3 LROC 19.0 Mini RF 12.6 Spacecraft Mass Allocation - Dry Table 3‑3- Spacecraft Mass Allocation - Dry

  10. Mass Allocation Summary • Margins meet GOLD requirement (20%) – 20.8% on CBE • Allocation – 710.3 kg • Current Best Estimate – 632.8 kg • Max Dry mass – 764.7 kg • System Margin – 54.4 kg (7.7%) • Or 79.4 kg (11.2%) including spin balance mass • Assume 1480 max LV capability

  11. Technical Resource AllocationsPower Un-Switched Power Instrument Heater Power Switched Power

  12. Power Allocations • Technical Resource Allocations Document, 431-SPEC-000112 • Power allocations include: • Un-Switched Power • Instrument Heater Power – Operational & Survival • Switched Power • Spacecraft Power Allocations • Switched and Un-Switched • Derived from Current Best Estimates • Contingency based upon Design Maturity Factor for each switch • Heater • Operational heater power allocations for each instrument/component are based on Beta=90° cold case orbit average predictions plus margin. • Survival heater power allocations for each instrument/component are based on Safe-hold orbit average predictions plus margin

  13. Power Allocation Driving Requirements • Worst Case is based on “S+Ka Orbit” mission phase from LRO Mission Concept of Operations Document, 431-OPS-000042 as documented in the Master Equipment List • Driving Requirements • Power System • MRD-103: System sized for 823W On-Orbit Average • Solar Array Properties • 1849W @ 35V • EOL properties for 14 month design life • Battery Spec • Max Depth of Discharge (DOD) is 30% • EOL properties for 18 month design life • Nominal 28V output • Energy Balance for Beta 0 case • 48 minute eclipse • full battery recharge in single orbit

  14. Power Allocation - Un-Switched Table 4‑1- Un-Switched Power Allocations

  15. Power Allocation – Instrument Heaters * - Current analysis shows no heater power is necessary  Table 4‑2 – Instrument Heater Power Allocations

  16. Power Allocation - Switched Table 4‑3 - Switched Power Allocations

  17. Power Allocation Summary • Margins meet GOLD requirement at SRR (15%) – 21% on CBE • On-Orbit Average designed for 823W power system (MRD-103) • Power Allocations set at 745W max for S+Ka Orbit, Beta 0 case • 10%+ margin on power system • Current Best Estimate for worst case power average is 680.4W • S+Ka Orbit from Mission Concept of Operations Plan • Margin = 21%

  18. Technical Resource AllocationsFlight Software Processor Memory 1553 Bus

  19. Data Allocations – Key Assumptions • 750 Processor or equivalent • GNC Software resident on Main Processor • Using cFE for core FSW • Interfaces include only: • 1553 bus interface • 1355 (Spacewire) • Baseline no science data processing/compression onboard

  20. Flight Software Allocation Summary * From GSFC-STD-1000 (GOLD Rules - FSW)

  21. LRO Processor Memory Utilization

  22. 1553 Allocation

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