ISTS 2004-r-07 R&D ON SPACE DEBRIS OPTICAL OBSERVATION TECHNOLOGIES

ISTS 2004-r-07 R&D ON SPACE DEBRIS OPTICAL OBSERVATION TECHNOLOGIES Atsushi Nakajima 1, Toshifumi Yanagisawa 1, Takeo Kimura 1, Takeshi Hoshino 1 and Fumihiko Futaba 2 1 Japan Aerospace Exploration Agency(JAXA) 7-44-1 Jindaiji-higashimachi, Chofu-shi, Tokyo 182-8522, JAPAN 2 Tokyo University of Science (E-mail: nakajima@chofu.jaxa.jp) Abstract Since 1999, we have been developing space debris observation technologies. For this purpose, small optical observation facilities were constructed; 0.35-m Schmidt Cassegrain(SC) telescope on the X-Y mount tracking system for LEO debris observation and 35 cm Newton-type telescope on the equatorial mount for GEO debris observation. High-speed read-out CCD camera with 4K 4K elements and its cooling system have been developing for the detection of faint objects. Automatic debris detection software has been also developing for the future efficient observation. This paper describes the space debris optical observation facilities and detecting technologies developed by Japan Aerospace Exploration Agency (JAXA). 1. Introduction About fifty years have passed since the first launch of the artificial satellite in the earth orbit. During the time, several thousand rockets and satellites have launched and the total mass will be estimated several thousand tons. These expensive rockets and satellites turn out debris when they finish their missions. Many of the debris still move around the earth, which brings increased anxiety of collision with the satellites in service or the International Space Station(ISS) under construction. Therefore, in the Institute of Space Technology and Aeronautics(ISTA), JAXA, the debris problem Copyright 2004 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. 1 has been investigated comprehensively from the viewpoint of observation, protection and prevention of occurrence. The consideration of debris problem requires the accurate information of present state of the contamination of real space environment. At the moment, Japan Space Forum(JSF) has finished the constructions of the optical observation facilities, named Bisei SpaceGuard Center(BSGC), at Bisei-town in Okayama prefecture. They are the 1.0 meter telescope with 3 degrees field-of-view(fov) and the 0.5 meter telescope with 2 degrees FOV, which are operated by Japan Spaceguard Association for GEO/GTO debris and asteroids observations. For the future and further observation technology developments, i.e. remote operation and the improvement of detection limit of faint space debris(i.e. small-size debris), two small aperture telescopes, 35 cm diameter, were prepared in the ISTA[1], [2]. The one is the LEO debris tracking X-Y mount system, which is located at JAXA headquarter in Tokyo (Chofu-city) by open-loop control based on the TLE(2-line- elements) information and manual calibration. The large space debris such as rocket boosters and ISS can be recognized its shape and attitude motion by using this long focal length telescope and its accurate tracking capability. The other facility is the equatorial mount system for the small size GEO debris observation, which is located at the Nyukasa-yama mountain in Nagano prefecture. The altitude is about 1,800 meters and the detectable star magnitude is about 19-magnitude and 21 magnitude-class asteroid were detected by this small aperture telescope by using the stacking method. High speed read-out and high efficiency back illuminated CCD cameras with 1K 1K and 2K

2K elements were used and 4K 4K CCD camera is now manufacturing. This CCD camera will be cooled by a sterling engine refrigerator. 2. Optical Observation Capability Space debris information at the present state will be summarized as follows: (1) Debris peak distribution in the LEO is about 1,000 km altitude. (2) The limitation of the catalogued small size LEO debris is about 10 cm diameter (3) The protection capability of the ISS is designed for the debris less than 1 cm size (4) 50 cm diameter debris in the GEO are catalogued For the item (1), active de-orbiting will be required in the future. JAXA/ISTA has investigated the method for recovering/repairing/throwing the satellites and launching rocket left in the orbit when the mission was finished. Electro-dynamic tether technology is a candidate for efficient orbit change system. For the item (2), we proposed a new method to detect the trajectories of small LEO debris. By counting the number of the lines within a time, the density of the debris distribution will be estimated in that area during the observation time. For the item (3), it is necessary to improve the protection capability of the ISS bumper up to larger size of debris, on the other hand, more smaller size of debris should be observed and catalogued. For the item (4), the optical observation capability must be improved to detect the faint object under 50 cm size of debris in the GEO. Although a large aperture telescope is preferable to detect faint objects, an adequate total system with a low noise CCD camera and image processing technique will realize the same capability with small budget. In the ISTA, it will be expected to detect a smaller size of debris under 50 cm by using a 35 cm telescope and a developed image processing software. Fig.1 express the capability of detection size of debris for variable orbit altitude. In usual, radar system observes LEO debris under a few thousands km, on the other hand, optical telescope has a role of observing more higher altitude orbits. By improving the optical observation technologies, the detectable area can be spread to the undetected areas as shown in Fig.1. GEO Small Debris LEO Small Debris 10 cm Optical Telescope Radar LEO Large Debris Fig.1 Detectable debris size for variable orbital altitude 3. LEO Debris Tracking Facility GEO For the LEO debris and large space structures observation, JAXA(formerly NAL) has operated X-Y mount high speed tracking facility at Chofu in Tokyo since 1999. The purposes of this facility are: (1) Tracking and orbit/attitude determination of large debris and large manned structure as ISS. (2) Co-operating of some facilities located at other observation sites for tracking the same object to determine the orbital parameters quickly and also monitoring large debris before re-entry such as MIR Space Station(re-entered on March 23, 2001(JST) at the south Pacific region) and rocket boosters. (3) Tumbling motion of LEO debris will be estimated by tracking and monitoring the light variations[3]. The tumbling information is necessary for capturing the debris to retrieve or repair in the future. Fig.2 shows the LEO debris tracking facility. The main telescope is 35 cm Schmidt Cassegrain with 3,910 mm focal length. The location is Lat.35.40 42, Long.139.33 24. 2

For small LEO debris observation, line detection method was proposed[4]. Fig.3 shows the observation result. By accumulating the pixel data along the direction of small debris path, it will be expected to detect 30 to 40 times darker LEO debris than usual method. The orbital parameters can t determine by this method directly, but the debris distribution in an area during a time can be estimated. Wide Field Canon TV lens VF50mm+ Vixen Vixen CCD CCD FOV 5.7 4.6 5.7 4.6 Narrow Field for Day Time) Takahashi FC60 + WATEC(WAT100N) FOV 1.47 1.1 1.47 1.1 Narrow Field(for Night) MIZAR SPDX-80FX + N.I.L. I Iö I 18mm 1 8mm + SONY Handycam(DCR-PC1) öfov 1.7 1.7 0.35 m SC Telescope CCD Guide Telescopes 3-Axis X-Y Mount Fig.2 LEO Debris Tracking Facility at JAXA/ISTA, 4. GEO Debris Observation Facility Fig.3 Trajectories of LEO small debris passed through a FOV of 0.6 0.6 deg. during 30 minutes. The red line is a catalogued number (SSC 17844) For the GEO debris detection/orbit determination and developments of automatic debris detection software, CCD camera cooling system by the refrigerator, the equatorial-mount 35 cm optical telescope was used. It was located in a 3 meter dome at Nyukasa-yama, shown in Fig.4. High speed read-out CCD cameras were developed. Fig.5 shows 1K 1K and 2K 2K CCD cameras and a 4K 4K camera is developing, shown in Fig.6. Nyukasa-yama Astronomical Observatory at Fujimi-town N35º54, E138º10 40, 1,800m Takahashi e-350, 355mm, f=1,248mm, F/3.6 Image Circle 70mm, FOV3.2º Nisshin Dome, 3 m diameter Showa Kikai, Equatorial Folk-Mount NIL, High Speed Read-out CCD FOV 1.2º 1.2º(2k 2k CCD ) FOV 2.4º 2.4º(4k 4k Mosaic CCD) Fig.4 GEO Debris Observation Facility at Nyukasa-yama 3

Back illuminated 1k 1k CCD Pixel size : 13 m 13 m Clock : 16bit/500kHz Read-out : 2sec Back illuminated 2k 2k CCD Pixel size : 13.5 m 13.5 m Clock : 16bit/1MHz, 2ch Read-out : 2sec Fig.5 One Tip CCD s(1k 1K and 2K 2K) The total read/write time of the one tip CCD camera is about 4 seconds. The Perche cooling system was used for these CCD cameras because of their easy handlings. was applied to the moving objects(i.e. asteroid and comet) detection software. For moving object observation, the image data were obtained by a fixed star tracking mode. The movements of the object in the fixed stars are automatically picked up by the stacking method. This technology is successfully transferred to the commercial moving object detection software (Stella Hunter Professional TM, AstroArts Inc.). This software needs more than 5 images on the same area to accumulate the target signals and to delete the influences of the fixed stars, automatically. The main characteristics of this method is pointed out the capability of detecting noise-level faint signals which can t find by naked eyes as shown in Fig.7. 40 new asteroids were detected in the 35 cm telescope image data by applying this software. The darkest object is about 21 magnitude, which is Conventional Method(Blink) Back illuminated 4k 4k Mosaic CCD Pixel size : 15 m 15 m Dimension : 61.4mm 61.4mm Read/Write : ca.10sec Fig.6 4K 4K Mosaic CCD Stacking Method Compare For the future remote operation, a maintenance free cooling system is necessary. A refrigerate cooling system instead of liquid nitrogen cooler is manufacturing and applying to the mosaic CCD camera and the temperature is controlled minus 100. An exposure time of observing GEO debris will be 5 to 10 seconds, then the read/write time from CCD to the PC is required as fast as possible for the efficient observation. The time is depend on the CCD tip characteristics, the clock is designed of 500kHz for the CCD42-40 of Marconi. The read/write time is comparable with observation exposure time. The evaluation will be planed this summer. 4. Moving Object Automatic Detection Fig.7 Comparison of Asteroid Detection Detection of moving objects and listing their positions and magnitude Blink expression of detected asteroid Automatic debris detection software has been developing by applying a stacking method[5]. Before applying to the debris detection, this method Fig.8 Example Function of Moving Object Detection software 4

equivalent to the capability of 1 meter large aperture telescope. Fig.8 Shows an example expression of this software. 5. Concluding Remarks JAXA/ISTA has been developing the space debris optical observation technologies. High speed read-out CCD camera were line-upped from 1k 1K to 2k 2K with Perche cooling and 4k 4K with refrigerator for remote observation. For smaller debris detections, the stacking method has been developed and applied to the commercial use of asteroids and comets detection software. For the evaluations of these technologies and image data acquisitions, LEO debris tracking facility and equatorial-mount telescope are used. During the mid-term plan of JAXA(Oct. 2003 to March 2008), these technologies will be established and contributed to the usual operations of space debris observations by the ground-based optical telescopes. References [1] A.Nakajima et.al.:space Debris Observation by Ground-Based Optical Telescopes, Proceedings of the 22 nd ISTS, 2000-n-03, Morioka, May 2000. [2] A.Nakajima et.al.:geo/leo Space Debris Optical Observation Facilities in NAL, Proceedings of the 23 rd ISTS, 2002-r-15, Matsue, May 2002. [3] T.Yanagisawa et.al.:detection of Small LEO Debris by Use of the Line Detectin Method, JSASS, Vol.51, No.597, Oct.,2003. [4] T.Yanagisawa et.al.: Motion and Shape Determination of LEO Debris Using Optical Telescope, 24 th ISTS, 2004-r-10, Miyazaki, June 2004. [5] T.Yanagisawa et.al.:detection of Small GEO Debris by Use of the Stacking Method, Transaction of the JSASS, Vol.44, No.146, Feb.,2002. 5