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Development of a coherent Dopplerlidarfor precision maneuvering and landing of space vehiclesFarzin Amzajerdian, Glenn D. Hines, Diego F. Pierrottet, Bruce W. Barnes,Aram Gragossian, Mitchell J. Davis, Tak-kwong Ng, Alexander D. Scammell,Adam BenShabat, Larry B. Petway, and John M. CarsonNASA Langley Research Center19th Coherent Laser Radar ConferenceJune 18-21, 2018
Frequency Modulated, Continuous Wave (FMCW) Waveform
3 segments waveform minimizes false alarms due to zero-crossing and signal ambiguity
NDL Measures velocity and range along three different laser beamsSimultaneous line-of-sight measurements are used to estimate:Velocity Vector (V)Altitude relative to local ground(No IMU data required)
Navigation Doppler Lidar (NDL)
Past landing missions used radars for vehicle position and velocity data in absence of GPSNDL offers an order of magnitude higher precision and much higher data quality (low false alarms) while reducing required size, mass, and powerNDL enables“precision navigation”to the designated landing locationNDL enables“well-controlled”descent, landing, and ascent maneuvers to within a few cm/secReduced touchdown impact loadslowerlandermassOptimized fuel consumptionlower mass and risk
NDL Replaces Radars on Space Vehicles
~200 kg
2008
2010
2012
2014
2017
GEN 2: 28 kg
Breadboard without real-time processing
GEN 1: ~ 60 kg
Fully-Autonomous Prototype
GEN 2.1: 17 kg
GEN 3: 10 kg
NDL development from breadboard to fully-autonomous prototype
rocket-powered free-flyer vehicles
GEN 3 NDL
Chassis 11”x9”x8”Optical Head 2” lenses
Fully-autonomous operationIntegrated real-time processorsRobust operation onboard different terrestrial vehicles
NDLOptical Head
Gantry Tests
NDL Characterization
NDL Setup
Calibrated Target on back of a truck driven on the runway
Operational Range Measurements at Langley AFB Runway
Mean Intensity
NDL Operational Range Measurement
Maximum Operational Range Predications
Measurement threshold
Lidar EquationTarget reflectivity = 0.5Humidity = 70%Visibility = 17 kmModerate Turbulence Cn2= 3e-14
Mars Perf Projectionwith nominal atmospheric and surface albedo
Moon Perf Projection
Range (m)
Relative Signal Intensity
Maximum operational ranges in Mars and Moon extrapolated from measured dataMars 5.7 kmMoon 7.5 km
Mean of measured intensity data
GEN 3 NDL Performance
a. Dependent on atmosphere and surface albedob. Errors dominated by the vehicle’s vibration and angular motions (1.7 cm/sec and 2.2 m in flight tests)c. Heatsink and fans module for terrestrial operation adds 1.5 kg and 10 W
Key NDL Features
Stable, Narrow Linewidth, Low Noise LaserStable and Low Noise Fiber AmpHighly Linear Modulation WaveformLowNoise, Flat Response, and Well-BalancedReceiverHigh Resolution FFT ProcessorRobust Signal Processing AlgorithmCompact ChassisEfficient Thermal DesignMechanically Robust
In-house built C&DH board20 layers and thousands traces
3-channel Dual-Balanced Receiver
Use “space-qualified” or “space-qualifiable” partsConduct radiation and thermal/vacuum tests at component/subsystem levelEfficient heat conduction to host vehicleRobust structureEMI resistance
NDL-3
ETU
Spaceflight Engineering Test Unit (ETU)
Future Work
Complete and test SpaceflightEngineering Test Unit (ETU)bymid 2019Flight tests onboard a high speed aircraft and a rocket-powered vehiclein summer2019Continue study and field testing for terrestrial applicationsAutonomous ground and aerial vehiclesHelicopter landing in degraded visual environments (DVEs)Other proprietary applicationsContinue technology advancementMiniaturizationExpand NDL capabilities for other space and terrestrial applications
Backup
Principle of Navigation Doppler Lidar
Time
Frequency
DetectorOutput(beat frequency)
Bandwidth
Period
Time delay is a measure of target range
Target velocity causes up and down beat frequencies to separate
Frequency Modulated, Continuous Wave (FMCW) Technique
NDL Modulation Waveform
NDL Real-Time Processor & System Controller
6 antennas each 22 cm diameter, 4 cm thick
130 cm x 50cm x40 cm
Optical Head
MSL DopplerRadar
Optical Head
Navigational Doppler Lidar
24cm
35cm
18 cmdiax 20 cm H
30X higher velocity and altitude precision3 orders of magnitude tighter beams40% reduction in power, 50% in mass, and 60% in size
Chassis
Comparison of NDL and MSL Radar
17cm
Approx. 450 m slant range30 degree glideslope
100m x 100 m hazard field
Navigation Doppler Lidar
Flash Lidar
DopplerLidarHead
Laser Altimeter
Shuttle Landing Facility, NASA-KSC
3-D Flash Lidar mapped the terrain for real-time hazard detection and avoidanceNDL provided data for precision navigation and soft landing at the selected site3 open loop flights (April 2014)3 closed loop flights (two in May 2014 and one in December 2014)
Morpheus Flight Demonstrations
0 10 20 30 40 50 60 70 80 90 100 110time (s)
350300250200150100500
Range (m)
1612840
velocity (m/s)
0 10 20 30 40 50 60 70 80 90 100 110time (s)
Velocity Magnitude
Altitude
Landing
Takeoff
Morpheus Flight Test Data
Comparison with IMU/GPS measurements
NDL data in excellent agreement with IMU/GPS/Altimeter dataNDL provides more accurate and precise vehicle state vector (position and velocity vector) than GPSNDL surface-relative measurements are highly precise with negligible bias
NDL LOS velocity compared to vehicle NAV using IMU, GPS, and a laser altimeter
0.20.150.10.050-0.05-0.1-0.15-0.2
LOS Residuals, m/sec
0 10 20 30 40 50 60 70 80 80 100 110Time, second
Ongoing Free-Flyer Test Campaign
465 m
10 m
300 m
Divert
100 m
Start 25 m/sdescent
500 m
20 m
Altitude
COBALT Payload = NDL + Terrain Relative Navigation (TRN) sensor + Navigation Filter
NDL
COBALT
NDL can enable precision navigation in GPS-deprived environmentsNDL can assist landing in degraded visual environments (DVEs) such as brownout conditionNDL can provide 3-D range and velocity map of surroundings
Non-Space Applications of NDL
Spaceflight Engineering Test Unit (ETU)Development Approach
Electronic partsUse “space-grade” or “space-grade EM” partsFew parts have no space-grade equivalentsChange design or qualify COTS parts (i.e., conduct radiation and thermal/vacuum tests)Photonic and fiber optic partsLeverage spaceflight qualification heritage when possibleCustom-design for space environments (vacuum, 0 g, radiation, thermal, vibration)Conduct radiation and thermal/vacuum tests as necessaryPerformTh/Vacand Vibration tests on major subsystemsSubject assembled ETU Chassis to environmental tests

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