Navigation Systems for Lunar Landing
Ian J. GravsethBall Aerospace and Technologies Corp.
March 5th, 2007
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Lunar Landing Problem Overview
What is needed─ Navigate to the correct area
Need to know position and orientation relative to the landing site
Measure altitude and velocity Identify Hazards in relative space
─ Land Safely Avoid Hazards (Steep Slopes, Rocks,
Holes, other structures, etc.) Land with acceptable velocities
─ Precision Landing Some landers require < 10 m final
targeting error Landing sites are more challenging than
Apollo-era sites ─ High contrast lighting for final approach
Worse than no natural lighting ─ Rougher terrain
A robust sensor or set of sensors are needed for a high reliability landing system
─ Notional sensors include an altimeter, a velocimeter, a terrain relative navigation sensor, and a hazard relative navigation sensor
Target Landing Zone
Lander Approach
Nav. Sensor measures Alt.,Vel., performs TRN
Final Approach Guided by hazard maps Target a good landing location
Possible Obscuring Dust Prior Lidar Maps and high resolution
images provide virtual surface view Inertial sensors give lander position
on map including hazards Safe Touchdown
Lidar Imager begins landing Zone hazard mapping
Rocks
Steep Slopes
Holes
Nav. Sensor provides precision guidance data
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Flash Lidar
Pros─ Sensor provides all required data types
Altimetry Velocimetry Terrain relative navigation Hazard detection Precision navigation when close to the surface
─ Low mass, power and volume─ System produces direct range measurements
The sensor provides 256 x 256 pixels, each with X, Y, Z, intensity and quality at 30 Hz.
Real time processing─ Light insensitive─ Self-correlated images are provided─ Self-contained navigation algorithms are
available
Cons─ No flight heritage
TRL of the system may be advanced through other space based Lidar applications
─ Lower number of pixels than an optical camera
LaserBeam
Lidar FOV
Flip-away Scanner
Z=70 km
Z=18 km
TRN, Altimeter, Velocimeter Operations
Z=2.5 km
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Visual Cameras
Pros─ Cameras are low mass, power and volume─ Descent cameras have previous flight heritage
(DIMES, etc.)─ Provides estimates of horizontal position and
velocity─ High resolution image data
Cons─ Cameras require good lighting conditions
May not work in scientifically interesting landing sites or in high contrast regions
─ Existing algorithms require an altitude estimate─ Doesn’t provide direct 3D image data
2D image locations
3D map locations
Images courtesy of JPL
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Radars
Pros Sensor functions during any lighting conditions Very accurate range and velocity
measurements Flight Heritage
─ Used on all Mars Landers
Cons Large mass, volume and power Hazard measurements with a phased array
system are available, but are very constrained─ Configuration, mass issues, resolution issues
Radars don’t generally perform well when they are close to landing
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Scanning Lidar
Pros─ Sensor provides all required data types─ Flight heritage for space missions
Cons─ Challenging alignment tolerances─ Unequal sampling distance during a scan─ Higher power and mass than a flash system─ Stitching data together in real time or faster
required for use of data Vehicle motion will distort the images
─ ~20% of the maximum ranging capability relative to a flash system
─ Significantly larger mass and power than a flash Lidar
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Geiger Counters (Kaktus Gamma Ray Altimeter)
Pros─ Only altimeter option that is currently in use for
this same problem (re-entry and landing of people on the Earth’s surface)
─ Extensive heritage─ Radio source is always “on”, does not require
power
Cons─ Ground roughness can affect accuracy
because the intensity of the reflected gamma-quantum flow is averaged over the entire diameter of the circle
─ Russian technology-politics, ITAR, contract with Energia
─ Radioactive source─ Limited range of operation─ Altitude and potentially velocity only
Images courtesy of JPL
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Landing Sensor Summary
Active─ Flash Lidar─ Scanning Lidar─ Radar─ Geiger counter
Passive─ Optical Sensors
Flash Lidar
Scanning Lidar
Optical Camera Radar
Geiger Counter
Degree of Difficulty / Relative Ranking
Needed Sensor Capabilities
Altitude Measurement
Easiest / Best Performance
Velocity Measurement
Medium Difficulty / Medium Performance
Position and Orientation
Most Difficult / Worst Performance
Hazard Detection
Sensor Characteristics
Works in all Lighting Conditions
Self-Correlated Images
Light Insensitive
Range of Operation
Low Mass
Low Power
Flash Lidar is the most attractive sensor for Lunar Landing