Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Ranjeet Shetty 234-A, Avionics Engineering Center, Russ College of Engineering and Technology, Ohio University Advisor: Dr. Chris Bartone Bi-Directional DGPS for Range Safety Applications

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center  Background  DGPS  Remote Positioning  Bi-Directional DGPS System  Instantaneous Impact Point  Overflight Exclusion Zone  Flight Corridor  Conclusion Outline

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center DGPS requires a Reference Station (surveyed location) that processes the GPS signals, derives the pseudo-range corrections with respect to its known location and transmits them to the mobile users in the area.  Common error sources are either corrected or eliminated  Accuracy can range from sub-meter to 10 meters Differential GPS

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center  Ionospheric Delay: m during the afternoon and 1 – 6 m at night. Dependent on latitude and time of day, solar cycle.  Tropospheric Delay: Up to 30 m for a low elevation satellite. Dependent on Elevation Angle.  Ephemeris Errors: Typically 1 – 3 m  Satellite Clock Error Errors Eliminated by DGPS

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Errors not eliminated by DGPS  Receiver Noise  Uncorrelated Multipath  Spatial Decorrelation : Changes with distance in Ionosphere and Troposphere  Temporal Decorrelation : Changes with time

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Differential Reference Station Mobile User Navigation Signals Differential Pseudo-range Corrections DGPS Illustration Data Link Antenna GPS Antenna GPS Space Segment GPS Antenna Data Link Antenna

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Smoothing Filter Measured Pseudo-range Measured Integrated Doppler SV Clock Corrections + - GPS AntennaData Link Antenna GPS Receiver PC with QNX operating system  SV Position Ephemeris Time Range Reference Position + -  Pseudo-range Corrections Clock Bias Estimation - + DGPS at Ground Station Freewave Radio

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center DGPS at Mobile User Smoothing Filter Measured Pseudo-range Measured Integrated Doppler Pseudo-range Corrections SV Clock Corrections GPS AntennaData Link Antenna GPS Receiver PC with QNX operating system Tropospheric Corrections High Accuracy Position Solution  Freewave Radio

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Remote-Positioning (stand-alone) System Navigation Signals Unmanned Airborne Vehicle (UAV) GPS Antenna Remote Positioning Ground Station (GPS stand-alone) GPS Space Segment Measurement and Position Data Link Antenna

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Remote-Positioning DGPS System Navigation Signals Unmanned Airborne Vehicle (UAV) GPS Antenna Remote Positioning Ground Station (DGPS) Measurement and Position Navigation Signals Data Link Antenna GPS Antenna GPS Space Segment Data Link Antenna

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Remote-Positioning DGPS at Mobile User Measured Pseudo-range Measured Integrated Doppler GPS Antenna Data Link Antenna GPS Receiver PC with QNX operating system Freewave Radio

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Smoothing Filter Measured Pseudo-range Measured Integrated Doppler SV Clock Corrections + - GPS AntennaData Link Antenna GPS Receiver PC with QNX operating system  SV Position Ephemeris Time Range Reference Position + -  Pseudo-range Corrections Clock Bias Estimation - + Remote-Positioning at Ground Station Freewave Radio Smoothing Filter  User’s Integrated Doppler User’s Pseudo-range Tropospheric Corrections SV Clock Corrections High Accuracy Position Solution

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Uplink Differential Pseudo-range Corrections  Enables high accuracy position solution at the user end  Enables auto pilot, precision landing, etc Downlink Measurement and Position  Enables high accuracy position solution of the remote user at the ground station  Can track the UAV from a remote position We want both - Simultaneously Positioning Requirements

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Bi-directional DGPS System Navigation Signals Unmanned Airborne Vehicle (UAV) GPS Antenna Remote Positioning Ground Station (DGPS) Measurement and Position Navigation Signals Data Link Antenna GPS Antenna Differential Pseudo- range Corrections GPS Space Segment Data Link Antenna

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Smoothing Filter Measured Pseudo-range Measured Integrated Doppler Pseudo-range Corrections SV Clock Corrections GPS AntennaData Link Antenna GPS Receiver PC with QNX operating system Tropospheric Corrections High Accuracy Position Solution  Freewave Radio + + Bi-directional DGPS Mobile User + + +

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Smoothing Filter Measured Pseudo-range Measured Integrated Doppler SV Clock Corrections + - GPS Antenna Data Link Antenna GPS Receiver PC with QNX operating system SV Position Ephemeris Time Range Reference Position + - Pseudo-range Corrections Clock Bias Estimation - + Freewave Radio Smoothing Filter  User’s Integrated Doppler User’s Pseudo-range Tropospheric Corrections SV Clock Corrections Calculated High Accuracy Position Solution + + Bi-Directional DGPS Ground Station  Transmitted High Accuracy Position Solution  + - Integrity Threshold Use/Don’t Use + +

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Instantaneous Impact Point Instantaneous Impact Point (IIP) - Continuous plot on the ground of where the vehicle would impact.  Computed from the vehicles instantaneous velocity, current position and time to impact  Displayed in real time during the flight IIP uncertainties  Less than 100 ft for the Eastern Range  Less than 1000 ft for the Western Range Impact Limit Lines (ILL) - Defined boundaries beyond which significant pieces of debris should not penetrate.

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center IIP Illustration t = t1 t = t2 Projection XX t = t1 t = t2 ILL IIP

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center  Debris Dispersion Radius(D max ): Radius of a circular area indicating limits for flight control and explosive containment.  Overflight Exclusion Zone: Area in close priximity to a launch point where mission risk is high. Should be clear of public.  Flight Corridor: Area on the earth’s surface estimate to contain majority of the hazardous debris from nominal flight. Launch Parameters

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Overflight Exclusion Zone D oez D max Launch Point Flight Azimuth

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Flight Corridor 10 NMi F C E D H I Downrange Area 5000 NMi Launch Area Launch Point 100 NMi Right Boundary Left Boundary Downrange Boundary Nominal Trajectory Uprange Boundary G B

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center Flight Corridor - Guided Launch Vehicles 10 NMi F C E D Downrange Area Launch Area Launch Point 100 NMi Right Boundary Left Boundary Downrange Boundary Nominal Trajectory Uprange Boundary G B Impact Range (D) Final Stage Impact Dispersion Area R

Ohio University Russ College of Engineering and Technology School of Electrical Engineering and Computer Science Avionics Engineering Center  DGPS historically used to provide high accuracy position solution at mobile user for their use.  DGPS Remote Positioning is applied to autonomous determination of a vehicle position at a remote location.  Application of DGPS for IIP application is new.  Bi-Directional DGPS System will provide high accuracy position solution at the mobile user as well as autonomous determination of vehicle position at a remote location for IIP applications. Conclusion