1. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D (In Brief) Texas A&M University Aerospace Engineering Department May/17/2002 Proj. leaders : Prof. John L. Junkins, Prof. John Valasek PostDoc. : Dr. Declan Hughes Grad. Students: Ju Young Du, Kiran Gunnam

2. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : Motivation A Local Positioning System (LPS) is required for close in multi-spacecraft navigation. Typical operations are rendezvous, docking, departing, formation flying, inspection/observation, articulated interaction. Provides augmentation for GPS, which must deal with performance detractors such as multipath reflections, diffraction errors, low bandwidth, dropouts.

3. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : Motivation A Visible/IR light based LPS offers negligible diffraction, high bandwidth, no dropouts. Multipath reflections are minimized by a restricted field of view. Optimal sensor Signal-Noise (S/N) ratio obtained by closed loop control of beacon intensity. System selects beacons from redundant set => robustness and flexibility.

4. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : Motivation VISNAV => visible/IR light based LPS => um (1micron) order wavelengths => negligible diffraction. VISNAV => high bandwidth (100Hz), and is robust with no dropouts. (want 10x>then control loop 10x10) Multipath reflections are minimized by a restricted (+-10 deg) field of view. (+_ 40 or >) Optimal sensor Signal-Noise (S/N) ratio obtained by realtime closed loop control of beacon intensity. (Tune for the right energy) Sensor only sees beacon, signals outside of 40KHz notch rejected => no pattern recognition problem. System selects beacons from redundant set => robustness and flexibility. Very small sensor => redundant sensors possible.

5. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : Spacecraft Docking Sensor transmits beacon selection/intensity to beacon controller via dig. IR signal. Sensor subsequently registers direction (azimuth, elevation) to beacon selected. 4+ beacon measurements => 6DOF Position/Attitude

6. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : Compound Sensor Sensor/beacon in one unit on each craft => 4DOF. At least one other beacon on one craft (needed for range and roll). Full 6DOF with minimal components.

7. Aerospace Engineering Department Texas A&M University, May/17/2002 PSD Sensor Photographs Full 4 beacon 100Hz +/-40deg. 6DOF sensor working in Laboratory. Optical filter to block visible light. Small 2.3”x3.3” 120 MFLOPS peak DSP computer. Wide angle lens focuses wide field of view onto Position Sensing Diode. Sensor = approx. 3” x 3” x 2”. Three beacon sizes (10W, 2.5W, 0.8W approx.).

8. Aerospace Engineering Department Texas A&M University, May/17/2002 Accurate 100 Hz update rate, 6DOF data with small low power sensor/beacons to 100+m. Accuracy varies from meters at 100m to sub-mm’s at < 1m; Higher accuracy possible with smaller field of view or slower update rate. Beacon signal modulation and optical filtering => excellent ambient light rejection. Real-time beacon selection/intensity control => minimizes power requirements. Pattern recognition problem eliminated. Very wide field of view, no moving parts. Distributed beacons => very large operating space, redundancy. Facing sun operation estimated appears feasible; still to be demonstrated. Next version several times smaller, will eliminate lens and use cheaper regular photodiodes instead of position sensing diode. Small redundant sensors => can optimize one for wide field of view, and the other for small field of view accuracy. Millimeter microwave (MMW) version being considered. VISNAV 3D : Conclusions

9. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : VISNAV LIDAR VISNAV => measures angles, no moving parts, wide field of view, fast data updates. Directed collimated beam LIDAR => measures distance, moving parts, slow lock on for wide field of view, possibly slow data updates. Proposed VISNAV LIDAR => measures distances, no moving parts, wide field of view, fast data updates. VISNAV LIDAR would use local feedback paths to compensate for electronic noise/drifts.

10. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV 3D : VISNAV LIDAR

11. Aerospace Engineering Department Texas A&M University, May/17/2002 VISNAV System AR&C Application First VISNAV system application. Beacons placed in NASA JSC NSTL room on walls and on a movable frame. Frame may be moved outside; used for docking simulations. VISNAV will calibrate differential GPS sensor system. NSTL