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LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements

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LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements & Implementation John Cavanaugh LOLA Instrument Systems Engineer – PowerPoint PPT presentation

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Title: LRO System Requirements Review Lunar Orbiter Laser Altimeter (LOLA) Investigation Requirements


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
  • 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

LOLA Instrument
DOE Beam Splitter
Radiator
Beam Expander
Receiver Telescope
Laser Bench
Main Optical Bench
Detectors Aft Optics (2 more on far side)
S/C Deck
Main Electronics Box
4
LOLA Heritage
  • Heritage Design Elements
  • Laser MLA, GLAS, SLA, MOLA
  • DPSSL NdYAG 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

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 DOCS
LRO E ICD 431-ICD-00008
LRO Gnd Sys ICD 431-ICD-00049
LRO M ICD 431-ICD-000NN
LOLA MICD 431-ICD-000089
LOLA EICD 431-ICD-00098
LOLA DICD 431-ICD-00108
LOLA TICD 431-ICD-000117
LOLA System Implementation Plan LOLA-PLAN-000N
LOLA Science and Functional Requirements LOLA-RQMT
-0002
LOLA Interface Drawings
LOLA Performance Assurance Implementation
Plan LOLA-PLAN-0003
LOLA Configuration Management Plan LOLA-PLAN-0001
LOLA Assembly Drawings
LOLA Sub-Assembly Drawings
LOLA CM DOCS
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 (Lamps version)
7
Mission Level RequirementsESMD-RLEP-0010
LRO Req. Level 1 Requirements Level 1 Requirements
Instr. LRO Mission Requirement Data Products
RLEP-LRO-M30 LOLA The 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 LOLA The 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 LOLA The 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 LOLA The LRO shall identify putative deposits of appreciable near-surface water ice in the Moons 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
Mission Level RequirementsESMD-RLEP-0010
LRO Req. Level 1 Requirements Level 1 Requirements
Instr. LRO Mission Requirement Data Products
RLEP-LRO-M80 LOLA The LRO shall assess meter-scale features of the lunar surface to enable safety analysis for potential lunar landing sites over targeted areas of 100km2 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 LOLA The LRO shall characterize the Moons 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
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
M30-LOLA M40-LOLA M90-LOLA IMR1 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
M30-LOLA M40-LOLA M90-LOLA IMR2 Provide 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 lt100 meter spacing within 5 degrees to the poles Design such that SNR gt 3dB and Pd gt 95. Drives laser energy and receiver aperture
M30-LOLA M40-LOLA M90-LOLA IMR3 Provide 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
M30-LOLA M40-LOLA M90-LOLA IMR5 Provide a global digital elevation model (DEM) with 1 m vertical resolution and lt1/25x1/25 grid spatial resolution. Product of range measurement with orbit pointing knowledge
10
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 IMR6 Provide 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 IMR4 Provide 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.
M60-LOLA M80-LOLA M90-LOLA IMR7 Provide 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
M60-LOLA M80-LOLA M90-LOLA IMR8 Provide means to verify optical alignment between LOLA LROC Alignment cube
11
LOLA System Level Requirements
Level 2 Req. Level 2a Requirements LOLA-RQMT-0002 Concept/Realizability/Comment
Reqt. no. LOLA Instrument Functional Requirement
IMR1 F3 Measure laser pulse time of flight (TOF) with better than 500 ps resolution from 0 to 5 milliseconds wrt laser trigger pulse. Coarse ctr. _at_ 20 MHz with TDC fine counter
IMR1 F6 Laser pulse repetition rate 28 Hz 0.1 Hz By design
IMR1 F8 Pdgt95 from 20 to 80 km altitude Laser energy Rx aperture
IMR2 IMR4 IMR8 F7 Produce 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
IMR2 IMR4 IMR8 F2 Determine laser pointing wrt LRO spacecraft reference to within 100 µrad Alignment cubes, on-orbit cal.
IMR2 IMR4 IMR8 F12 Crosstalk between any two channels lt 1 Beam spacing, Rx FOV
IMR3 IMR5 MRD-040 F1 Time 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
IMR3 IMR5 MRD-040 F5 Total ranging error lt 1 m w/ nadir pointing and post processing of S/C orbit and attitude. Synch. Measurements w/ LRO pointing orbit data
IMR3 IMR5 MRD-040 F9 Maintain long term ranging bias error to 1 m over the mission lifetime. LRO USO stability
12
LOLA System Level Requirements
Level 2 Req. Level 2a Requirements LOLA-RQMT-0002 Concept/Realizability/Comment
Reqt. no. LOLA Instrument Functional Requirement
IMR6 F10 Measure the transmitted laser energy with better than 5 (1 sigma) relative accuracy (shot to shot). Pulse integrator
IMR6 F11 Measure the received energy in each return signal with 5 (1 sigma) relative accuracy for received energies Er Such that 0.1fJ lt Er lt 10 fJ Pulse integrator
IMR7 F4 Measure receive pulse widths from 6 to 100 ns with better than 0.5 ns resolution TDC
13
LOLA Subsystem Level RequirementsTransmitter
Level 2 Req. Level 3 Requirements LOLA-RQMT-0002 Concept/Realizability/Comment
Reqt no. Laser Design Requirements
F3, F4, F6, F7, F8 L1 Wavelength 1064.3 nm 0.1nm NdYAG fundamental
F3, F4, F6, F7, F8 L2 Configuration Diode Pumped Solid State CrNdYAG Efficiency
F7, F8 L3 Pulse energy before beam expander 2.7 mJ 0.3 mJ Signal link
F6 L4 Pulse rate 28.0 Hz 0.1 Hz For coverage
F3, F4 L5 Pulse width 6 ns 2 ns Timing resolution
F7, F12 L6 Output beam divergence 1.8 mrad 0.2 mrad Sample size on moon
F7, F12 L7 Spatial mode TEM00 Radially symmetric sample
F7 L8 Beam diameter 1 mm 0.2 mm Beam expander input
F8 B1 Transmission efficiency gt 13 per spot Reqd to meet signal link
L3, L9 B2 Input energy density NTE 0.6 J/cm2 Below damage threshold
F7 B3 Output beam divergence 100 ?rad 10 ?rad 5 m spots at 50 km
F7, F12 B4 Beam separation wrt center beam 500 ?rad 20 ?rad Coverage
F7 B5 Pattern clocking wrt instrument coordinates 26 2 Sample pattern
14
LOLA Subsystem Level RequirementsReceiver
Level 2 Req. Level 3 Requirements LOLA-RQMT-0002 Concept/Realizability/Comment
Reqt no. Laser Design Requirements
F3, F7, F8 RE01 Receiver aperture gt 0.015 m2 14 cm diameter refractive telescope similar to MLA
F7 RE02 Receiver PFOV 1.4 mrad Defines telescope size
F7, F8, F12 RE02a Receiver IFOV (each detector) 400 ?rad 20 ?rad To match transmitter pattern
F8 RE03 Detector quantum efficiency 40 Signal link (photon detection)
F8 RE04 Optics transmission 70 Signal link (throughput)
F8 RE06 Filter bandwidth 0.8 nm FWHM Signal link (minimizes background)
F8 RE07 Transmission loss due to contamination 0.5 dB up to launch Signal link (throughput)
F8 RE08 Transmission loss due to misalignment 0.5 dB up to launch Signal link (misalignment)
F12 RE09 Receiver crosstalk lt 1
15
LOLA Subsystem Level RequirementsSignal
Processing
Level 2 Req. Level 3 Requirements LOLA-RQMT-0002 Concept/Realizability/Comment
Reqt no. Laser Design Requirements
F1 RSP1 Time stamp laser pulses to within 100?s of LRO 1 PPS For post-processing location
F3, F4 RSP2 Time of flight resolution better than 500 ps Aperture uncertainty portion of 10 cm error, defines TDC
F3, F4 RSP3 Receiver impulse response 6 ns FWHM Required for resolution, amplifier detector bandwidth 140 MHz
F5, F9 RSP4 OCXO frequency drift 10-7 over single shot measurement And 10-7 over 3 hours Short and midterm OCXO stability
F3, F7, F8 RSP5 Capture and characterize one return per shot per detector Link margin high, processing like MOLA
F3, F4 RSP6 Measure signal pulse widths from 6 to 100 ns Minimum to 3X expected max
F10 RSP7 Measure laser output energy with better than 5 relative accuracy Shot to shot relative accuracy required for expected ice reflectivity measurement
F11 RSP8 Measure return pulse energy with better than 5 relative accuracy Shot to shot relative accuracy required for expected ice reflectivity measurement
F3 RSP9 Measure pulse time of flight from 0 to 5 ms full range Encompasses checkout extended mission orbits X 4
F8 RSP10 Programmable detector voltage gain from 0.1 to 10 with linear response from 0.3 to 10 VGA implementation same as MLA, GLAS
16
LOLA Data Product Traceability
Data Description Required 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
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
    gt97 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 IT

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

21
Instrument Current Status
  • Major trade studies since Instrument inception
    which have been closed
  • Oscillator Count and Location gt LRO provides
    signal and reliability (mass savings)
  • Be vs. Aluminum gt Be (mass savings)
  • BK7 vs Sapphire gt BK7 (mass savings)
  • Interface comms gt1553 (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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