optical navigation system michael paluszek, joseph mueller, dr. gary pajer princeton satellite...

Optical Navigation System

Michael Paluszek, Joseph Mueller, Dr. Gary Pajer

Princeton Satellite Systems

EUCASS

July 4-8, 2011

St. Petersburg, Russia

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Summary of Talk

• Introduction• Background• Sensor Design• Simulation Results• Future Work

New Name: Integrated Communications and Optical Navigation System

ICONS

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Sensor Design• Dual articulated telescopes• On-board calibration cube and calibrated light sources

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Overall System

• Communications architecture

• Reference satellites in earth orbit

• Range, range rate, timing and communications

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Introduction

• Optical Navigation Systems in Past Missions

– 1966-72 Apollo. Backup navigation. Position fix measuring angle between star and a landmark.

– 1996 NEAR Shoemaker. Rendezvous with asteroid Eros. Visual identification of craters for rapid orbit determination.

– 1999 NASA Deep Space 1. Autonomous Orbit Determination with Optical Triangulation.

– 2003 Hayabusa. Rendezvous with asteroid Itokawa. Wide angle cameras and LIDAR.

– 2006 SMART-1. AMIE camera for Earth/moon and star camera.

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Introduction

• So what is noteworthy about this optical navigation system?• Fully automated and flexible spacecraft navigation, attitude

determination and comunications system using optical measurements range, range rate and GPS measurements if available– Can operate just with optical measurements

• For use on:– Low earth orbit GPS denied missions– Geosynchronous orbit missions– Planetary and lunar orbit– Deep space

• Objective: Low power / low mass / low cost orbit determination system that can be used for a wide range of missions.

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Background

• Optical Measurements form the basis of the system– Angles between planets– Angles between landmarks– Angles between planet/star or

landmark/star– Width of planets

• Errors are a combination of sensor errors and uncertainties in the measured objects– Ephemeris uncertainty– Figure uncertainty

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Optical Measurement Geometry

• l1, l2 and u are from the ephemerides

• θ1, θ2 and θ3 are the observables• Want to know the vector r• For relative orbit determination want

to know ρ1 and ρ2

• Angle Categories:– θ1 Planet / Planet (centroid or

feature)– θ2 Feature / Feature (same planet) or

Planet Chordwidth– θ3 Planet-Star

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Spacecraft

θ1

θ2

ρ2

ρ1

θ3

I1 I2

ur

Star

Planet

Planet

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Navigation System

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Planet Centroiding

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Planet Centroiding

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Algorithms

• Unscented Kalman Filter for Recursive Estimation (UKF)– Better performance than EKF due to highly nonlinear predict and update

functions– Uses nonlinear model and measurement equations to propagate a

sampling of “sigma points” around the mean– Captures first and second order nonlinear terms– Eliminates need to explicitly calculate Jacobian– Used for recursive attitude determination and orbit determination– Can incorporate any measurement

• Batch algorithm runs in background as check on recursive estimation and method for resetting the recursive algorithm– Reset based on covariances of the two methods

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Simulation Results-Messenger

• Plots show observables• Larger chords improve resolution• Angular separation determines if one

telescope can see two planets (rare)

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Simulation Results-Messenger

• Shows planets used for estimation

• Inner planets’ ephemerides are more accurate– Errors continue to

decrease as more observations are added

• Errors less than 200 km using planets through Jupiter (1-5)

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Simulation Results-Pluto

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Simulation Results-Messenger

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Hardware Development

• Optical transmitter and receiver• Telescope with imaging chip• Oscilloscope shows binary

signal

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Future Work

• Mass expected to by 4-8 kg depending on size of optics

• Cost target is < $2M USD• Building a complete terrestrial prototype

– Building a 3U CubeSat version with orthogonal telescopes without articulation

– Dual CubeSats will also perform relative navigation

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Conclusions

• The Optical Navigation System provides a one device solution to navigation, communications and attitude determination

• Performance is sufficient for orbit control

• Outer solar system performance is limited by ephemeris knowledge of major planets

• Many combinations of precision encoders, imaging chips and telescope focal length and aperture are possible to optimize the sensor for specific missions

• Optical communications capability integrates, timing, range and range rate into the system