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