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

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

3. Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements
Level 2 Req.
Level 3: Requirements
Concept/Compliance
Paragraph
Requirement
MRD-12
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
The polar orbit shall be 90 degrees +/- 1 degrees longitude.
SA tracks to meet this requirement/Complies
MRD-19
MRD-099
MRD-102
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
The EPS mass shall not exceed the allocation as specified LRO Technical Resource Allocations Specification (431-SPEC ).
Complies

4. 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
The EPS shall support all observatory operational modes and mission phases as defined in the Lunar Reconnaissance Orbiter Mission Assurance Requirements (431-RQMT ) and summarized here:
Pre-launch/Launch Readiness
Launch and Lunar Transfer
Orbiter Activation/Commissioning
Measurement Operations
Extended Mission operations
End-of-Mission/Disposal

5. 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 VDC nominal measured at the loads during all mission phases through use of the LRO Power Subsystem Electronics (PSE).
Complies
MRD-103
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
Max. capability is 823W orbit average
MRD-21
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

6. Lunar Reconnaissance Orbiter (LRO) EPS System Level 2 Flow Down Key Requirements
Level 2 Req.
Level 3: Requirements
Concept/Compliance
Paragraph
Requirement
MRD-31
The EPS power consumption shall not exceed the allocation as specified LRO Technical Resource Allocations Specification (431-SPEC ).
Complies
MRD-20
MRD-106
MRD-107
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
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
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

7. Lunar Reconnaissance Orbiter (LRO) EPS Block Diagram

8. 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

9. 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