Long base-line stereoscope for Earth-bound orbits surveillance experiments in Romania

1. Long base-line stereoscope for Earth-bound orbits surveillance experiments in Romania Octavian CRISTEA, BITNET CCSS, ROMANIA SCI 229 ET NATO SSA, DLR Bremen, 14-16 Dec. 2009

2. Short comments on sensors for space objects surveillance • The ground based stereoscope project for LEO surveillance experiments • The ground-to-space stereoscope project for high orbit object tracking experiments This Presentation is Unclassified SCI 229 ET NATO SSA, DLR Bremen 14-16 Dec. 2009

3. A. Sensors for space objects surveillance SPACE OBJECTS SURVEILLANCE: The combined tasks of detection, characterization, correlation, and orbit determination of space objects. Typical GROUND BASED SENSORS PASSIVE ACTIVE OPTICAL Tracking telescope Satellite laser ranger RADIO Satellite broadcast monitoring station Radar

4. SPACE BASED SENSORS PASSIVE ACTIVE OPTICAL ? LEO telescope for GEO orbits surveillance ? ? RADIO Real-time surveillance of Earth neighborhood is a big challenge

5. Sensor limitations There is no instrument which can detect any object on any orbit …

6. B. The ground based stereoscope project for LEO surveillance • MAIN TASKS: • Very wide area search and detection of LEO objects using electro-optical sensors • Robotic operation of sensors • Orbit depth recovery using parallax • LEO orbit determination. THE ELECTRO-OPTICAL SENSOR Can we use a “classical” setup (telescope + CCD + PC) for building the stereoscope ? The answer is YES but, the probability to detect a LEO object with unknown orbital parameters is incredible small !

7. In a wide search mission, an optical sensor collects frames of data on consecutive directions in order to find objects in its range of detection. If FOV is the telescope Field of View, and we take 10 s only for integration time, data transfer to PC and re-pointing the telescope to a new direction, it means that a complete survey (all directions) takes: T (seconds) = 10 x (360 x 180) / FOV For FOV = 1 x 1 (a big one for a telescope) => T = 180 hours while a LEO object visible pass is few minutes only! Illustrating how small is the probability to detect a space target with unknown orbital parameters – roughly speaking, it is like shooting a flying bird with closed eyes.

8. t1 t2 t1 t2 Several cooperating sensors can increase this probability A sensor taking consecutive snapshots of the sky within its FOV. Cooperative sensors taking N snapshots of the sky at any given moment.

9. THE REAL PROBABILTY TO DETECT AN UNKNOWN TARGET IS SIGNIFICANTLY SMALLER SINCE OTHER FACTORS HAVE TO BE TAKEN INTO ACCOUNT: • The sky must be clear and dark 1 • The sensor must be in the Earth’s shadow 2 • The space object must be above the sensor’s horizon 3 • The space object must be illuminated by the Sun 4 The visibility window is very small The good thing is that if we wait enough, sooner or later any Earth orbiting object will enter the sensor FOV during the visibility window. The bad thing is that it might take a very long time until the sensor will detect the unknown object. This is the challenge of real-time surveillance of space objects. REMARKS: Requirement 1 does not apply to space-based optical sensors; 1, 2 & 4 do not apply to radars.

10. The first option in the stereoscope design was to integrate an “all sky” camera with big aperture and small f-theta distortion. • Problems: • such a lens is very expensive • best COTS lens we could find has 2% f-theta distortion • small threshold detection magnitude • the Moon will be in the FOV many times. • The second (and actually) option is to integrate an “all azimuth” sensor using few COTS wide FOV and big aperture lenses. • This solution: • decreases the angular distortion • increases the angular resolution (1 to 3 arc min is the target) for a designed FOV of 3600 x 520 • 6 to 7 threshold detection magnitude should be easy to reach.

11. Stereoscope setup. Pair cameras take simultaneous consecutive photos of the sky. The stereoscope’s base-line is 37 Km, a compromise between simultaneous detection of low altitude objects from two locations and triangulation accuracy.Pair cameras synchronization is made through GPS. Geometric calibration of the image is made by matching captured stars in the image with an astronomical catalogue of stars.The recovery of orbital depth is made by correlating matching feature points from pairs of simultaneous images. The project is in the concept development phase. Contributing organizations: BITNET CCSS (stereoscope setup and operation), the Technical University of Cluj (robotic stereoscopy), the Astronomical Observatory of Cluj (astrometry), the Romanian Research Authority (financial support). The project consortium is open for cooperation.

12. C. The ground-to-space stereoscope project idea MAIN IDEA: a stereoscope made from One LEO telescope One (or several) ground based telescope (s) which will take simultaneous photos of the same high orbit space object. NEOSSAT – Near Earth Object Surveillance Satellite Such a stereoscope has a very long, time dependent base-line.

13. NEOSSAT MISSION & SPACECRAFT Spacecraft developed by the Canadian Space Agency (CSA) together with Defense Research and Development Canada (DRDC).

14. The Spacecraft • Microsatellite platform • Mass about 75 Kg, available power approximately 35 Watts, dimensions 1 x 0.8 x 0.4 m • Pointing stability of 0.5 arcsec in pitch and yaw for extended periods • Reaction wheels, no propulsion • Sensors: sun sensor, star tracker, magnetometers, solar cells • Orbit: 500-850 km dawn-dusk sun-sync • The Science Payload • Customized 15 cm aperture F/6 Maksutov telescope • Filed of view is 0.85 deg • CCD array 1k x 1k pixels, sensitivity range 310 to 1100 nm • Limiting magnitude: approximately 20 v.mag with 100 sec exposure • Pixel scale: 3 arcsec/pixel

15. THE GROUND SEGMENT WHICH IS IN DEVELOPMENT AT BITNET Rural area, 1200 m altitude, 55 Km far from Cluj-Napoca, electromagnetic quiet zone, no light pollution. • The testbed will host: • a ground station to downlink data from the satellite • a robotic telescope (probably 40 cm aperture) for acquisition of satellite or other space object metric and signature data • GPS for time synchronization • VSAT for internet connectivity through a geostationary telecommunication satellite.

16. EXAMPLES OF POSSIBLE JOINT EXPERIMENTS USING A SPACE-BASED AND A GROUND-BASED TELESCOPE Simultaneous space object signature and position information acquisition from Earth and space Comparison of ground spacecraft signature with on-orbit spacecraft signature for space object identification tests. In addition, the spacecraft will be rapidly changing its orientation with respect to the ground-based sensor, and “truth” knowledge of these changes can be made available. Evaluation of the roles played and value added by a space-based telescope. Comparison of observation-based attitude and pose estimation with NEOSSat truth data from telemetry

17. Octavian Cristea is the founder and managing director of BITNET CCSS Ltd., a small contract research company in Romania specializing in technology applications development and/or demonstration (surveillance sensors, satellite communications, software). Since 2004 he is deeply involved in the development of the SofS activities in Romania (consulting, space surveillance systems analysis and design, project proposals development). Before founding BITNET CCSS, he worked as scientist at the Romanian Institute of Space Sciences and at the Babes-Bolyai University, being involved in gravitation and space-time related research. He is a diplomat physicists of the Babes-Bolyai University, specialized in several technical areas over the years (sensors, space technology applications, commercial satellite communications).

18. Thank You for Your Attention!