Optical Navigation System Michael Paluszek, Joseph Mueller, Dr. Gary Pajer Princeton Satellite Systems EUCASS July 4-8, 2011 St. Petersburg, Russia

2 Summary of Talk  Introduction  Background  Sensor Design  Simulation Results  Future Work New Name: Integrated Communications and Optical Navigation System ICONS

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

4 Overall System  Communications architecture  Reference satellites in earth orbit  Range, range rate, timing and communications

5 Introduction  Optical Navigation Systems in Past Missions – Apollo. Backup navigation. Position fix measuring angle between star and a landmark. –1996NEAR Shoemaker. Rendezvous with asteroid Eros. Visual identification of craters for rapid orbit determination. –1999NASA Deep Space 1. Autonomous Orbit Determination with Optical Triangulation. –2003Hayabusa. Rendezvous with asteroid Itokawa. Wide angle cameras and LIDAR. –2006SMART-1. AMIE camera for Earth/moon and star camera.

6 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. 6

7 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

8 Optical Measurement Geometry  l 1, l 2 and u are from the ephemerides  θ 1, θ 2 and θ 3 are the observables  Want to know the vector r  For relative orbit determination want to know ρ 1 and ρ 2  Angle Categories: –θ 1 Planet / Planet (centroid or feature) –θ 2 Feature / Feature (same planet) or Planet Chordwidth –θ 3 Planet-Star 8 Spacecraft θ1θ1 θ2θ2 ρ2ρ2 ρ1ρ1 θ3θ3 I1I1 I2I2 u r Star Planet

9 Navigation System

10 Planet Centroiding

11 Planet Centroiding

12 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

13 Simulation Results-Messenger  Plots show observables  Larger chords improve resolution  Angular separation determines if one telescope can see two planets (rare)

14 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)

15 Simulation Results-Pluto

16 Simulation Results-Messenger

17 Hardware Development  Optical transmitter and receiver  Telescope with imaging chip  Oscilloscope shows binary signal

18 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

19 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