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John Cavanaugh LOLA Instrument Systems Engineer NASA GSFC

LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation. John Cavanaugh LOLA Instrument Systems Engineer NASA GSFC. LOLA Organization Chart. LOLA Overview. LOLA Instrument. Functional Description

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John Cavanaugh LOLA Instrument Systems Engineer NASA GSFC

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  1. LRO System Requirements ReviewLunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation John CavanaughLOLA Instrument Systems EngineerNASA GSFC

  2. LOLA Organization Chart

  3. LOLA Overview LOLA Instrument Functional Description Using a single pulsed laser split into five beams LOLA will measure : • Range to the Lunar Surface • Pulse time of flight method • Single threshold crossing • leading edge & trailing edge timing • Each measurement referenced to S/C MET • Surface Direct Reflectance • Transmitted laser energy before splitter • Received signal energy from each of five detectors From these measurements and LRO S/C data products the LOLA Science team will produce : • Lunar Digital Elevation Model • Localized surface roughness and slope data for landing site characterization • Surface reflectance data • Imaging of permanently shadowed regions • Lunar geodetic coordinate system • LRO precision orbit and trajectory • Lunar gravity model DOE Beam Splitter Radiator Beam Expander Receiver Telescope Laser Bench Detectors & Aft Optics (2 more on far side) Main Optical Bench S/C Deck Main Electronics Box

  4. Heritage Design Elements Laser : MLA, GLAS, SLA, MOLA DPSSL Nd:YAG slab oscillator Crossed-porro resonator configuration Passive Q-switch ( MLA, GLAS ) Laser diodes from Coherent ( MLA ) Beryllium beam expander telescope ( MLA ) Receiver Telescope : MLA Refractor design Beryllium tube Fiber coupling to aft optics Detector : MLA, GLAS, SLA, MOLA SiAPD hybrid with programmable gain (MLA, GLAS) Range Measurement Unit : MLA Low-speed coarse counter High resolution ASIC Power Converters : MLA, GLAS, MOLA Signal Processing Algorithm : MLA, MOLA Range gate tracking Active gain & threshold control with signal & noise feedback Implemented in 80C196 (MLA), 8086 (MOLA), 80K85 (LOLA) Beryllium structure : MLA, GLAS, MOLA LOLA Heritage

  5. LRO-LOLA Instrument Document Tree LRO Project Requirements ESMD-RLEP-0010 LRO Mission Requirements Document 431-RQMT-00004 LRO Technical Resource Allocations 431-RQMT-00112 LRO Pointing and Alignment Requirements LRO CM DOC’S LRO E ICD 431-ICD-00008 LRO M ICD 431-ICD-000NN LRO Gnd Sys ICD 431-ICD-00049 LOLA EICD 431-ICD-00098 LOLA TICD 431-ICD-000117 LOLA MICD 431-ICD-000089 LOLA DICD 431-ICD-00108 LOLA Science and Functional Requirements LOLA-RQMT-0002 LOLA System Implementation Plan LOLA-PLAN-000N LOLA Interface Drawings LOLA Configuration Management Plan LOLA-PLAN-0001 LOLA Performance Assurance Implementation Plan LOLA-PLAN-0003 LOLA Assembly Drawings LOLA Sub-Assembly Drawings LOLA CM DOC’S LOLA Integration and Test Plan LOLA-PLAN-00NN LOLA System Engineering Management Plan LOLA-PLAN-0010 LOLA Component Drawings LOLA Schematics LOLA Safety Plan LOLA-PLAN-00NN LOLA Risk Management Plan LOLA-PLAN-00NN LOLA Contamination Control Plan LOLA-PLAN-0004

  6. LRO Document Flowdown (Lamp’s version)

  7. Mission Level RequirementsESMD-RLEP-0010

  8. Mission Level RequirementsESMD-RLEP-0010

  9. LOLA System Level Requirements

  10. LOLA System Level Requirements

  11. LOLA System Level Requirements

  12. LOLA System Level Requirements

  13. LOLA Subsystem Level RequirementsTransmitter

  14. LOLA Subsystem Level RequirementsReceiver

  15. LOLA Subsystem Level RequirementsSignal Processing

  16. LOLA Data Product Traceability

  17. LOLA Constraints on LRO • Provide stable timebase frequency for LOLA range measurement • Operate LOLA continuously throughout the measurement phase. • Maintain S/C pointing within ±1° of nadir for >97% of the measurement phase. • Provide post-processed pointing knowledge to within 150 µrad each axis (3-sigma) at 1 second intervals. • Angular Exclusion : 1.5 millirads around boresight. • Align LOLA beam pattern to within ±1° of S/C velocity vector. • Provide precision positioning knowledge data of LRO spacecraft for post-processing of LOLA data. • Provide a 1 PPS time signal and associated MET message on orbit. • Provide post-processed time with 3 ms accuracy relative to UTC. • Provide means to reference LOLA optical axis to S/C coordinates during I&T

  18. LOLA Block Diagram

  19. LOLA Development Flow

  20. LOLA Verification TESTING (Levels): • Ranging Performance (Instr. & S/C): • Provide simulated range returns via pulsed optical signals and CW background into each detector via fiber optic test port. • Signal Processing (Instr. & S/C): • Simulate lunar orbit signal conditions with changing return and background signals, verify false alarm rate using ranging performance test data • Reflectivity Measurements (Instr): • Monitor laser output energy with calibrated GSE meter. • Inject optical pulses into receiver and measure independently with calibrated meter. • Optical Alignment (Instr. & S/C): • Verify boresight alignment at instrument assembly, before and after vibe and during TVAC • Measure LOLA optical axis wrt ref. cube on instr. • Measure LOLA ref. cube wrt S/C alignment cube after integration, vibe, TVAC and shipment to launch site • Laser Performance (Instr. & S/C): • Continuous monitoring of laser output energy • Periodic measurement of beam quality (during alignment) ANALYSES: • Structural • Thermal • STOP (Structural-Thermal-Optical) • Optical Stray Light Analysis and Test result are assessed with respect to requirements for compliance • Requirements tracking includes verification methods and compliance criteria

  21. Instrument Current Status • Major trade studies since Instrument inception which have been closed • Oscillator Count and Location => LRO provides signal and reliability (mass savings) • Be vs. Aluminum => Be (mass savings) • BK7 vs Sapphire => BK7 (mass savings) • Interface comms =>1553 (flight experience) • Major ongoing trade studies which could impact either Instrument top-level requirements • MEB coupling to Optic Deck • Laser Ranging for Orbit Determination • Analyses currently being performed: • Structural • Thermal • Reliability • Hardware currently in development: • Laser • Electrical (Power, Analog, Digital)

  22. LOLA Development Schedule

  23. Summary • Network Schedule Established • Grass-roots Budget Estimation In Process • Instrument Requirements Document Baselined • Constraints on LRO have been flowed down and captured in the MRD. • Breadboarding Successful • Diffractive Optic Element (DOE) • Laser • Fiber optic alignment • SRR/PDR Completed, “Passed with Reservations” • Delta-PDR required. • Double check requirements flow-down to Level IV • Check readiness of subsystems for final design • Ready to move to preliminary design

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