Navigation Systems for Lunar Landing

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Navigation Systems for Lunar Landing

• Ian J. Gravseth
• Ball 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 lt 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
• 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

Lidar FOV
LaserBeam
Flip-away Scanner
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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
• Doesnt 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 dont 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 Earths 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

    Flash Lidar Scanning Lidar Optical Camera Radar Geiger Counter Degree of Difficulty / Relative Ranking Degree of Difficulty / Relative Ranking Degree of Difficulty / Relative Ranking Degree of Difficulty / Relative Ranking
Needed Sensor Capabilities Altitude Measurement           Easiest / Best Performance Easiest / Best Performance Easiest / Best Performance  
  Velocity Measurement           Medium Difficulty / Medium Performance Medium Difficulty / Medium Performance Medium Difficulty / Medium Performance Medium Difficulty / Medium Performance
  Position and Orientation           Most Difficult / Worst Performance Most Difficult / Worst Performance Most Difficult / Worst Performance 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
• Flash Lidar
• Scanning Lidar
• Radar
• Geiger counter
• Passive
• Optical Sensors

Flash Lidar is the most attractive sensor for
Lunar Landing