Transcript Document

Navigation Systems for Lunar Landing
Ian J. Gravseth
Ball Aerospace and Technologies Corp.
March 5th, 2007
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
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Flash Lidar
 Pros
─ Sensor provides all required data types
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Lidar FOV
Altimetry
Velocimetry
Terrain relative navigation
Hazard detection
Precision navigation when close to the surface
Laser
Beam
─ 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
Flip-away Scanner
TRN, Altimeter, Velocimeter Operations
Z=70 km
Z=18 km
 Cons
─ No flight heritage
Z=2.5 km
 TRL of the system may be advanced through
other space based Lidar applications
─ Lower number of pixels than an optical camera
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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
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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
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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 gammaquantum 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
Flash
Lidar
Needed Sensor
Capabilities
Scanning
Lidar
Optical
Camera
Radar
Geiger
Counter
Degree of Difficulty /
Relative Ranking
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
 Active
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Flash Lidar
Scanning Lidar
Radar
Geiger counter
 Passive
─ Optical Sensors
Flash Lidar is the most attractive sensor for Lunar Landing
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