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NASA’s Goddard Space Flight Center 11 - 1 LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation.

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Presentation on theme: "NASA’s Goddard Space Flight Center 11 - 1 LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation."— Presentation transcript:

1 NASA’s Goddard Space Flight Center LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation John Cavanaugh LOLA Instrument Systems Engineer NASA GSFC

2 NASA’s Goddard Space Flight Center LOLA Organization Chart

3 NASA’s Goddard Space Flight Center LOLA Overview 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 Receiver Telescope Laser Bench Main Optical Bench Radiator Beam Expander DOE Beam Splitter Detectors & Aft Optics (2 more on far side) S/C Deck Main Electronics Box LOLA Instrument

4 NASA’s Goddard Space Flight Center LOLA Heritage 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

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

6 NASA’s Goddard Space Flight Center LRO Document Flowdown (Lamp’s version)

7 NASA’s Goddard Space Flight Center Mission Level Requirements ESMD-RLEP-0010 LRO Req. Level 1: Requirements Instr. LRO Mission RequirementData Products RLEP- LRO-M30 LOLAThe LRO shall collect global geodetic data using spatially resolved topography with a 10m vertical accuracy with a 2km cross-track and 30m along track sampling at the equator. Global digital elevation model of the moon with 1 m vertical resolution and 100 m horizontal resolution with 1 km average cross track sampling at the equator. RLEP- LRO-M40 LOLAThe LRO shall obtain geodetic lunar global topography (at landing-site relevant scales - 30m down-track and 50m cross-track) with spatial resolution of 50m at the polar regions (within 5 degrees of the poles), and 1km at the equator. Global topography with 1 m vertical resolution and 100 m horizontal resolution with 1 km average cross track sampling at the equator. RLEP- LRO-M60 LOLAThe LRO shall obtain landform-scale imaging of lunar surfaces in permanently shadowed regions at 50m spatial resolution. Digital elevation model of topography in permanently shadowed polar regions with 50m horizontal resolution, 1m vertical resolution RLEP- LRO-M70 LOLAThe LRO shall identify putative deposits of appreciable near-surface water ice in the Moon’s polar cold traps at a 100m spatial resolution. Reflectance data from the permanently shadowed regions (PSRs) to identify surface ice signatures at a limit of 4% ice surface coverage by area

8 NASA’s Goddard Space Flight Center Mission Level Requirements ESMD-RLEP-0010 LRO Req. Level 1: Requirements Instr. LRO Mission RequirementData Products RLEP- LRO-M80 LOLAThe LRO shall assess meter-scale features of the lunar surface to enable safety analysis for potential lunar landing sites over targeted areas of 100km^2 per the LRO Landing Site Target Specification Document. Topography, surface slopes, and surface roughness at 25-m spacing over a 70-m wide field of view (FOV) swath at up to 50 selected potential landing sites. RLEP- LRO-M90 LOLAThe LRO shall characterize the Moon’s polar region (within 5 degrees of the poles) illumination environment at relevant temporal scales (i.e., typically that of hours) to a 100m spatial resolution and 5 hour average temporal resolution. Map of the polar regions poleward of latitudes 86° with a vertical resolution of 10 centimeters (cm) and a spatial resolution of 25 to 35m after one year, which will identify potential sites of optimal solar power generation.

9 NASA’s Goddard Space Flight Center LOLA System Level Requirements Level 1 Req. Instrument Level 2: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Requirement no. or para. LOLA Instrument Measurement Requirement M30-LOLA M40-LOLA M90-LOLA IMR1 IMR1a: Provide range measurement from the LRO orbit to the lunar surface with better than 1 m vertical accuracy. Laser pulse time-of-flight measurement, each pulse time referenced to S/C MET IMR1b : Provide range measurements with an along track posting of ≤30 m from the 50 km nominal LRO altitude. 28 Hz pulse repetition rate, beam pattern IMR2Provide range measurements at the above (IMR1) ranging accuracy and sampling rate continuously with ≥95% single sample spot detection probability for one year to achieve an average ground track spacing of ~1 km at the equator and <100 meter spacing within 5 degrees to the poles Design such that SNR > 3dB and Pd > 95%. Drives laser energy and receiver aperture IMR3Provide the geodetic location of each laser footprint on the lunar surface to within the laser footprint size. Time stamp each pulse wrt S/C MET IMR5Provide a global digital elevation model (DEM) with 1 m vertical resolution and <1/25°x1/25° grid spatial resolution. Product of range measurement with orbit & pointing knowledge

10 NASA’s Goddard Space Flight Center LOLA System Level Requirements Level 1 Req. Instrument Level 2: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Requirement no. or para. LOLA Instrument Measurement Requirement M70-LOLA IMR6Provide lunar surface reflectance measurements of the laser pulses at better than 10% relative accuracy (shot to shot and spot to spot) for received energy greater than 0.1 fJ in permanently shadowed regions of the lunar surface. Pulse integrator circuit on transmit & receive channel. M60-LOLA M80-LOLA M90-LOLA IMR4Provide five separate laser spots on the lunar surface from each laser pulse and measure the time of flight from each spot. The size of each laser spot is 5 meters (±1m) in diameter and separated by 25 meters center to center at 50 km nominal spacecraft altitude Beam splitter after laser provides far field pattern. IMR7Provide better than 10 cm resolution range and return pulse width measurement on single shot and each spot to assess slope and surface roughness characteristics. Measure leading & trailing edge pulse timing on each received pulse IMR8Provide means to verify optical alignment between LOLA & LROC Alignment cube

11 NASA’s Goddard Space Flight Center Level 2 Req. Level 2a: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Reqt. no. LOLA Instrument Functional Requirement IMR1 F3Measure laser pulse time of flight (TOF) with better than 500 ps resolution from 0 to 5 milliseconds wrt laser trigger pulse. Coarse 20 MHz with TDC fine counter F6Laser pulse repetition rate = 28 Hz ±0.1 HzBy design F8P d >95% from 20 to 80 km altitudeLaser energy & Rx aperture IMR2 IMR4 IMR8 F7Produce five laser footprints each with 5m diameter +/- 0.5m nadir pointing with 25m +/-1m spacing between adjacent spots at 50km altitude. Beam splitter w/ pattern aligned to LRO velocity F2Determine laser pointing wrt LRO spacecraft reference to within 100 µrad Alignment cubes, on-orbit cal. F12Crosstalk between any two channels < 1%Beam spacing, Rx FOV IMR3 IMR5 MRD-040 F1Time stamp laser pulses to better than ±100 microseconds with respect to the LRO S/C 1 second timing reference. Synchronize LOLA counters to MET pulse F5Total ranging error < 1 m w/ nadir pointing and post processing of S/C orbit and attitude. Synch. Measurements w/ LRO pointing & orbit data F9Maintain long term ranging bias error to ≤ 1 m over the mission lifetime. LRO USO stability LOLA System Level Requirements

12 NASA’s Goddard Space Flight Center Level 2 Req. Level 2a: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Reqt. no. LOLA Instrument Functional Requirement IMR6 F10Measure the transmitted laser energy with better than 5% (1 sigma) relative accuracy (shot to shot). Pulse integrator F11Measure the received energy in each return signal with 5% (1 sigma) relative accuracy for received energies Er Such that 0.1fJ < Er < 10 fJ IMR7 F4Measure receive pulse widths from 6 to 100 ns with better than 0.5 ns resolution TDC LOLA System Level Requirements

13 NASA’s Goddard Space Flight Center Level 2 Req. Level 3: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Reqt no. Laser Design Requirements F3, F4, F6, F7, F8 L1Wavelength nm ±0.1nmNd:YAG fundamental L2Configuration : Diode Pumped Solid State Cr:Nd:YAGEfficiency F7, F8L3Pulse energy before beam expander : 2.7 mJ ±0.3 mJSignal link F6L4Pulse rate : 28.0 Hz ±0.1 HzFor coverage F3, F4L5Pulse width : 6 ns ±2 nsTiming resolution F7, F12L6Output beam divergence : 1.8 mrad ±0.2 mradSample size on moon F7, F12L7Spatial mode : TEM 00 Radially symmetric sample F7L8Beam diameter : 1 mm ±0.2 mmBeam expander input F8B1Transmission efficiency > 13% per spotReq’d to meet signal link L3, L9B2Input energy density NTE 0.6 J/cm 2 Below damage threshold F7B3 Output beam divergence : 100  rad ±10  rad 5 m spots at 50 km F7, F12B4 Beam separation wrt center beam : 500  rad ±20  rad Coverage F7B5Pattern clocking wrt instrument coordinates : 26° ±2°Sample pattern LOLA Subsystem Level Requirements Transmitter

14 NASA’s Goddard Space Flight Center Level 2 Req. Level 3: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Reqt no. Laser Design Requirements F3, F7, F8 RE01Receiver aperture > m 2 14 cm diameter refractive telescope similar to MLA F7RE02Receiver PFOV : 1.4 mradDefines telescope size F7, F8, F12 RE02a Receiver IFOV (each detector) : 400  rad ±20  rad To match transmitter pattern F8RE03Detector quantum efficiency ≥ 40%Signal link (photon detection) F8RE04Optics transmission ≥ 70%Signal link (throughput) F8RE06Filter bandwidth ≤ 0.8 nm FWHMSignal link (minimizes background) F8RE07Transmission loss due to contamination ≤0.5 dB up to launchSignal link (throughput) F8RE08Transmission loss due to misalignment ≤0.5 dB up to launchSignal link (misalignment) F12RE09Receiver crosstalk < 1% LOLA Subsystem Level Requirements Receiver

15 NASA’s Goddard Space Flight Center Level 2 Req. Level 3: Requirements LOLA-RQMT-0002 Concept/Realizability/Comment Reqt no. Laser Design Requirements F1RSP1 Time stamp laser pulses to within ±100  s of LRO 1 PPS For post-processing location F3, F4RSP2Time of flight resolution better than 500 psAperture uncertainty portion of 10 cm error, defines TDC F3, F4RSP3Receiver impulse response 6 ns FWHMRequired for resolution, amplifier detector bandwidth 140 MHz F5, F9RSP4OCXO frequency drift ≤10 -7 over single shot measurement And ≤10 -7 over 3 hours Short and midterm OCXO stability F3, F7, F8 RSP5Capture and characterize one return per shot per detectorLink margin high, processing like MOLA F3, F4RSP6Measure signal pulse widths from 6 to 100 nsMinimum to 3X expected max F10RSP7Measure laser output energy with better than 5% relative accuracyShot to shot relative accuracy required for expected ice reflectivity measurement F11RSP8Measure return pulse energy with better than 5% relative accuracy F3RSP9Measure pulse time of flight from 0 to 5 ms full rangeEncompasses checkout & extended mission orbits X 4 F8RSP10Programmable detector voltage gain from 0.1 to 10 with linear response from 0.3 to 10 VGA implementation same as MLA, GLAS LOLA Subsystem Level Requirements Signal Processing

16 NASA’s Goddard Space Flight Center LOLA Data Product Traceability DataDescriptionRequired Inputs Level 0 Each shot : -Leading & trailing edge signal event counts -Transmitted pulse energy ADC counts -Received pulse energyADC counts Each second : - Background noise counts, threshold ADC readbacks, event counts - Housekeeping counts of T, I, V, laser pump LRO LOLA telemetry Level 1 Housekeeping values converted to engineering units Event counts converted to delay times in seconds Energy counts converted to Joules Background counts converted to Watts LOLA calibration data Level 2 Range measurements converted to altitude Range measurements converted to pulse spread values Energy measurements converted to reflectance 1st iteration of surface location LRO: Time, orbit and attitude products Level 3 Initial DEM products: - Topography - Slope - Surface roughness - Reflectance - LRO precision orbits and trajectory files LOLA crossover analysis LRO: POD products Level 4 Parameter set defining lunar geodetic coordinate system Global topography model & spherical harmonic coefficients Global gravity model & spherical harmonic coefficients LOLA DEM products LRO precision orbits and trajectory files

17 NASA’s Goddard Space Flight Center 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 NASA’s Goddard Space Flight Center LOLA Block Diagram

19 NASA’s Goddard Space Flight Center LOLA Development Flow

20 NASA’s Goddard Space Flight Center 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 NASA’s Goddard Space Flight Center 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 NASA’s Goddard Space Flight Center LOLA Development Schedule

23 NASA’s Goddard Space Flight Center 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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