Power Philip Luers NASA/GSFC Code 561 August 16-17, 2005

Lunar Reconnaissance Orbiter (LRO) EPS Level System Requirements Traceability Level 1- LRO Requirements ESMD-RLEP-0010 Level 2- LRO Mission Requirements Document 431-RQMT-000004 LRO Technical Resource Allocations 431-RQMT-000112 LRO Electrical Systems Specification 431-SPEC-000008 LRO Mechanical Systems Specification 431-SPEC-000012 LRO Thermal Systems Specification 431-SPEC-000091 Level 3- LRO Electrical Power Subsystem Spec. 431-SPEC-000013 Level 4- LRO Power Subsystem Electronics (PSE) Spec. 431-SPEC-000016 LRO Solar Array Spec. 431-SPEC-000037 LRO Battery Specification 431-SPEC-000032

Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements Level 2 Req. Level 3: Requirements Concept/Compliance Paragraph Requirement MRD-12 3.3.1.1 The SA shall support a primary circular polar mapping orbit with a nominal mean altitude of 50 +/- 20 km. Altitude is measured to mean lunar surface. SA analysis done for this orbit/Complies MRD-13 3.3.1.2 The polar orbit shall be 90 degrees +/- 1 degrees longitude. SA tracks to meet this requirement/Complies MRD-19 MRD-099 MRD-102 3.3.3.1.5 The nominal DOD during a typical lunar orbit shall be limited to 30% with 1 cell failure. In addition the battery shall be capable of supporting a DOD of 60% for launch phase and 80% for lunar eclipse periods and other mission modes for a total of not to exceed 10 cycles. Analysis done for worst case eclipse/Complies MRD-029 3.2.2.1 The EPS mass shall not exceed the allocation as specified LRO Technical Resource Allocations Specification (431-SPEC-000112). Complies

Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements Level 2 Req. Level 3: Requirements Concept/Compliance Paragraph Requirement MRD-098 3.2.3 The LRO power system shall be a Direct Energy Transfer (DET) design distributing main bus power only to all instruments and subsystems. Complies MRD-50 3.1.22.1 The EPS shall support all observatory operational modes and mission phases as defined in the Lunar Reconnaissance Orbiter Mission Assurance Requirements (431-RQMT-000004) and summarized here: Pre-launch/Launch Readiness Launch and Lunar Transfer Orbiter Activation/Commissioning Measurement Operations Extended Mission operations End-of-Mission/Disposal

Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements Level 2 Req. Level 3: Requirements Concept/Compliance Paragraph Requirement MRD-32 1.1 The bus voltage is maintained between 21-35 VDC nominal measured at the loads during all mission phases through use of the LRO Power Subsystem Electronics (PSE). Complies MRD-103 3.1.2.2.2 The LRO EPS shall support the total power allocation of the LRO spacecraft bus and instrument suite with margins as specified in LRO Technical Resource Allocations 431-RQMT-000112. Max. capability is 823W orbit average MRD-21 3.1.1.1 The Orbiter shall be designed for a one-year mission life (after reaching lunar orbit and post commissioning activities which are expected to be 2 mos.). The primary mission shall be followed by an extended mission with a total mission life of up to 60 months as resources allow. The extended mission is not to drive design requirements or resources. EPS shall support a reduced load extended mission/Complies

Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements Level 2 Req. Level 3: Requirements Concept/Compliance Paragraph Requirement MRD-31 3.1.2.2.6 The EPS power consumption shall not exceed the allocation as specified LRO Technical Resource Allocations Specification (431-SPEC-000112). Complies MRD-20 MRD-106 MRD-107 3.3.2.1.11 Hardware over current protection of the main power bus is done for a maximum of 48 switched services. This is accomplished with the use of Solid State Power Controllers (SSPC) with re-settable circuit breaker capability. MRD-105 3.1.2.2.3 The LRO EPS shall provide an unregulated 22-35Volts (V) bus as measured at the PSE to support a peak load of 1500W for a period of 5 minutes. MRD-104 3.1.2.2.9 To insure compliance with voltage specifications the spacecraft will present a minimum load to the power bus of 180W whenever the system is powered up. System complies

Lunar Reconnaissance Orbiter (LRO) EPS Block Diagram

Lunar Reconnaissance Orbiter (LRO) EPS Verification Summary Analysis System energy balance, Solar array sizing Control loop simulation Failure Modes and Effects (FMEA), Reliability, Worst-case Component Tests PSE ETU Functional Limited environmental PSE Flight Full environmental Battery Life cycle Qual and acceptance testing Solar Array Spacecraft Level Full functional Orbiter-level Environmental Mission cycle

Summary The power group has been working closely with systems to understand and define the EPS requirements. Requirements have been defined sufficiently enough to allow the EPS ETU development to proceed with confidence. Power handling and switching margins have been incorporated to insure accommodation of any increases, the system is robust Presently proceeding with ETU board layouts and fabrication The EPS is ready to continue with detailed design