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International scientific optical network for space debris research

"Advanced in Space Research"

I. Molotova,b, V. Agapova,b, V. Titenkoc, Z. Khutorovskyb, Yu. Burtsevd, I. Gusevae, V. Rumyantsevf,
M. Ibrahimovg, G. Kornienkoh, A. Erofeevah, V. Biryukovf,i, V. Vlasjukj, R. Kiladzek, R. Zallesl, P. Sukhovm,
R. Inasaridzek, G. Abdullaevag, V. Rychalskyn, V. Kouprianove, O. Rusakove, E. Litvinenkoe, E. Filippove

a Keldysh Institute of Applied Mathematics, Miusskaja sq. 4, Moscow, 125047, Russia
b JSC "Vimpel" International Corporation,4thstreet of 8 Marta 3, Moscow, 125319, Russia
c Zverev Krasnogorsky Zavod, Rechnaya str. 8, Krasnogorsk-7, 143400, Russia
d Space Force of Russian Ministry of Defence, Moscow, Russia
e Central (Pulkovo) Astronomical Observatory, Pulkovskoe chaussee 65/1, St.-Petersburg, 196140, Russia
f Scientific-research institute"Crimean Astrophysical Observatory", Nauchny, 98409, Ukraine
g Ulugh Beg Astronomical Institute, Astronomicheskaya str. 33, Tashkent, 700052, Uzbekistan
h Ussuriysk Astrophysical Observatory, Gornotaeznoe, 692533, Primorsky Kray, Russia
iCrimean Laboratory of Shtenberg Astronomical Institute, Nauchny, 98409 Ukraine
jSpecial Astrophysical Observatory, Nizhnij Arkhyz, Zelenchukskaya, 369167, Karachaevo-Cherkesia, Russia
kAbastumani Astrophysical Observatory, Kazbegi ave, 2a, Tbilisi, 99532, Georgia
lObservatorio Astronomico Nacional, Casilla, 346, Tarija, Bolivia
mScientific-research institute "Astronomical Observatory" of Mechnikov Odessa National University, Ilpha and Petrova str. 55/1, Odessa, 65122, Ukraine
nNational Control and Space Facilities Test Center, Vitino Village, 97419, Sacskiy Region, Ukraine

Abstract

A joint team of researchers under auspices of the Center for Space Debris Information Collection, Processing and Analysis of the Russian Academy of Sciences collaborates with the 15 observatories around the world to perform observations of space debris. For this purpose, 14 telescopes were equipped with charge-coupled device (CCD) cameras, Global Positioning System (GPS) receivers, CCD frame processing and ephemeris computation software with the support of the European and Russian grants. Many of observation campaigns were carried out in collaboration with the Astronomical Institute of the University of Bern (AIUB) team operating Zimmerwald observatory and conducting research for the European Space Agency (ESA) using Tenerife/Teide telescope for searching and tracking of unknown objects in the geostationary region (GEO). More than 130,000 measurements of space objects along the GEO arc of 340.9 that were collected and processed at Space Debris Data Base in the Ballistic Center of the Keldysh Institute of Applied Mathematics (KIAM) in 2005-2006 allowed us to find 288 GEO objects that are absent in the public orbital databases and to determine their orbital elements. Methods of discovering and tracking of small space debris fragments at high orbits were developed and tested. About 40 of 150 detected unknown objects of 15-20.5m were tracked during many months. A series of dedicated 22-cm telescopes with large field of view for GEO survey tasks is in process of construction. 7 60-cm telescopes will be modernized in 2007.

1. Introduction

The problem of studying the real population of space debris objects in the GEO region is extremely important. On the one hand, geostationary orbit represents an unique area of the near space from the point of view of solving the various tasks (television and communication services, weather monitoring, data relay, etc.), and, on the other hand, it is a limited natural resource which requires preservation for future use. There is no natural mechanism of self-cleaning here, similar to the low Earth orbit (LEO) region (decay of space debris fragments in the Earth atmosphere). Most of the GEO objects will live eternally, moving along the orbit. Therefore, the program of GEO objects investigation using a 70 m dish antenna radar facility in Evpatoria, Crimea of Ukraine was established in 2001 (Molotov et al., 2004). At the same time, the work on arranging a scientific optical telescope network was initiated for the purpose of improving the ephemeredes of radar targets (Agapov et al., 2004), as the 70 m antenna in Evpatoria (RT-70) had a 3.6 arcmin beam width, and available orbital data precision was not enough for pointing RT-70 to space objects. Since 2003, a scientific optical network carries out the observations of the sample of GEO objects under auspices of the Ballistic Center of the Keldysh Institute of Applied Mathematics (KIAM), Russian Academy of Science. In 2004, first attempts to detect and track small GEO fragments of space debris were made using the AT-64 telescope in Nauchny, Crimea (Volvach et al., 2006), and a collaboration with European observatories was established (Agapov et al., 2005). Since 2005, the observations of International Scientific Optical Network (ISON) were carried out on a regular basis (Molotov, 2005). The list of participating observatories with the characteristics of each telescope involved, obtained results statistics, and future plans is presented below.

2. Scientific cooperation of former Soviet Union observatories

The first GEO object observations within this project were carried out in April 2001 at Pulkovo observatory which has a long history of astrometric satellite observations. It was the 10-cm AKD telescope that made the first photographic frame of the "Sputnik" rocket body on October 10, 1957. In next years, Nauchnij, Mayaki and Goloseevo observatories joined this activity. Then, in 2002-2003, the work on identifying the present condition of all optical observatories of the former Soviet Union (FSU) and negotiations for possibility of their participation in the project of scientific network was performed. This allowed us to elaborate the program of refurbishing and modernization of the telescopes involved, that was accomplished step by step with the support of the grant no. 03-70-567 of the International Association for the Promotion of Co-operation with Scientists from the New Independent States of the FSU and the grant no. 09.255.52/053 of the Ministry of Education and Science of the Russian Federation during 2004-2006. 14 optical telescopes were equipped with CCD cameras and GPS receivers to arrange the ISON for space debris research: 2.6-m ZTSh, 64-cm AT-64, and 22-cm SR-220 in Nauchnij, 65-cm refractor and 22-cm SR-220 in Pulkovo, 60-cm Zeiss-600 in Maidanak, 40-cm double Zeiss astrograph in Kitab, 40-cm double Zeiss astrograph in Ussuriysk, 40-cm double Zeiss astrograph in Abastumani, 60-cm RC-600 in Mayaki, 23-cm expedition astrograph in Tarija, 70-cm AZT-8 in Chuguev, 70-cm AZT-8 in Gissar, 22-cm SR-220 in Tiraspol. The operational group for planning and scheduling ISON observations and the technical group providing a necessary support for ISON observatories, developing the dedicated software and technical solutions, and arranging the training courses, were created. Apex II, a universal software platform for astronomical image processing, being developed at the Pulkovo observatory, was distributed among the observers. One of the peculiarities of this software is the ability to process images with trailed reference stars which appear during 5-10 s exposures taken without sidereal tracking, using the point spread function fitting technique (Kouprianov, 2006, submitted).

The geographic positions of the FSU observatories collaborating with ISON are presented in Fig. 1, while the characteristics of the telescopes involved - in Table 1. This table also displays the development plans for year 2007.

It is planned to divide the ISON telescopes into a number of dedicated subsystems. The first subset for regular GEO region surveillance between 130W and 210E will consist of 7 automated 22-cm telescopes SR-220 (see Fig. 2) with large field of view (FOV), up to 20 square degrees (Terebizh, 2001). Two test surveys arranged with SR-220 in Nauchnij displayed the high performance of the proposed solution. 100% of the catalogued GEO objects down to 15m and, partially, HEO objects were detected in sky areas of 20 x 20 and 30 x 30 in few hours of observations. Four SR-220 will be put into operation in the first half of 2007 in Nauchnij, Pulkovo, Ussuriysk, and Tiraspol. The astrographs of 23 cm and 40 cm size will be used to track the unknown objects detected in the surveys on a long measurement arc, and also for GTO objects observations.

The second subset, intended for more efficient searching and tracking of GEO objects with brightness of 15-18m, will be arranged. AT-64 in Nauchnij, RC-600 and SR-500 in Ussuriysk with FOV of about 2x2 will be a basis for this subsystem. In addition, correctors will be installed on Zeiss-600 in Simeiz, Zelenchuk, Maidanak, and Tarija to obtain FOV of about 1. These Ziess-600 telescopes will be provided with CCD cameras in 2007. The telescopes of 2.6-m ZTSh in Nauchnij, Zeiss-1000 in Simeiz and Zelenchuk, 1.5-m AZT-22 in Maidanak, Zeiss-2000 in Terskol and 1.6-m AZT-33IK in Mondy will be used for investigation of GEO fragments with brightness of 19-21m. The news of ISON are regularly published in a dedicated web site: www.lfvn.astronomer.ru.
3. Observations and results

ISON activity was coordinated mainly by the Center on Collection, Processing and Analysis of Information on Space Debris (CCISD) developed and operated on the basis of the Ballistic Center at the KIAM, Russian Academy of Sciences. First ISON observations of tens of GEO and HEO objects were carried out in support of the very long baseline interferometry radar experiments with Evpatoria RT-70 transmitter. Later, in addition, a sample of GEO objects was regularly observed to verify their presumable explosions predicted using the Pulkovo Laplace motion theory (Kiladze at al., 2003). Since June 2004, the continuous coordinated observation campaign for the GEO region was conducted jointly with Zimmerwald observatory of the Astronomical Institute of the University of Bern (AIUB) and observatories of the PIMS (the UK government asset for the surveillance of space with observatories in the UK, Gibraltar and Cyprus), aimed at searching, detection, and subsequent tracking of unknown GEO objects, determination of their orbital parameters, and orbital evolution estimation (Agapov et al., 2005). More than 130,000 measurements for space objects along the GEO arc of 340.9 (between 130.3W and 210.6E) were collected and processed at the CCISD in 2005 and 2006. Results of orbital determinations for 60 objects were published in the 7th issue of the European Space Operation Center (ESOC) "Classification of Geosynchronous Objects" (Serraller and Jehn, 2005), for 103 objects in the 8th issue (Hern?ndez and Jehn, 2006), and for 138 objects in the 9th issue (Arregui and Jehn, 2007) as unidentified objects in section 4.10.as unidentified objects in section 4.10.

The ISON program of observations of faint space debris objects which, presumably, emerged in events of fragmentation of some resident GEO objects started in October 2004. The main goals of the program are searching as many as possible faint fragments and continuous tracking the objects detected to analyze their orbital evolution and physical properties, to identify the possible parent object, and to estimate the level of their danger for operational satellites. European observatories in Zimmerwald (AIUB) and Teide at Tenerife (ESA) joined this program in 2005 (these observatories carry out own program of statistical surveys of the faint fragments under the ESA activities since 2001 (Jehn et al., 2006). AT-64 and ZTSh telescopes in Naucnij and Zeiss-1000 in Tenerife were searching fragments using the predetermined strategy in selected search fields; after the detection of an unknown fragment, it was tracked on a one-two hours arc in order to make possible rediscovery of the fragment on the next night. Fragments observed on at least a two-night interval were numbered 900xx if detected in Nauchny, or 430xx if detected in Zimmerwald or Tenerife. The numbered objects were followed up with Zimmerwald, Nauchny, Maidanak, Mondy, Nizhniy Arhyz, Mayaki and Ussuriysk. Also the trial observations of fragments were successfully fulfilled in Tarija, Evpatoria, Simeiz, Terskol, and Chuguyev. It was demonstrated that it is possible to track faint GEO objects on a long GEO arc from Bolivia to the Far East. The high capacity of the ISON was demonstrated in January 2006 during observations of the MSG 2 cooler cover 1 m in diameter and 10 cm thick. This operational fragment was discovered in Zimmervald in almost real time after the cover separation, then it was followed up in Simeiz, Nauchny, Maidanak, Mondy, and Ussuriysk. Results of the orbit determination based on observations obtained by the ISON were provided to the National Aeronautics and Space Administration and few months later the cover was observed and catalogued by the US Space Surveillance network.

The fields for fragment search were chosen at the points where the apparent density of catalogued GEO objects in the right ascension - declination space has maximum, or where fragments of presumably exploded objects cross the GEO ring and their parent objects' orbits (Sochilina et al., 2004). In the two-year period, 150 unknown objects of 15-20.5m were detected, and about 25,000 measurements in 1400 series were obtained. The statistics of results is presented in Table 2. The growth of the discovery rate of fragments was mostly due to involvement of the Tenerife telescope and the second larger FSU telescope ZTSh in Nauchny. The latter was equipped with the IMG1001E grade 1 CCD camera in February 2005, and had spent about 3-4 nights per month around the new Moon for the space debris observations. It will be equipped with the PL1001E grade 0 CCD camera in 2007 to provide fast photometry measurements.

63 faint objects were observed on several night time intervals that allowed us to estimate their area to mass ratio (AMR). The distribution of magnitude and area to mass ratio of the discovered fragments are shown in Fig. 3 and Fig. 4. The existence of clouds of fragments which were produced by explosions of Ekran-2, Ekran-4 and Transtage 68081E was confirmed. About 40 objects with relatively low AMR were tracked on time intervals from few months to two years, which has proved that such kind of objects may be catalogued in principle. The orbit of the 90022 fragment of Ekran-4 with brightness of 17m which was discovered with AT-64 in Nauchnij on April 30, 2006 was determined with high accuracy. A trial radar experiment for 90022 using the transmitting 70-m antenna in Evpatoria (Crimea, Ukraine) and the receiving 64-m antenna in Kalyazin (near Moscow, Russia) was arranged on July 7, 2006 for testing purpose.

The research shows that objects having high AMR (300 to 13000 times larger than that for 'normal' spacecrafts and spent rocket bodies), first discovered by the AIUB team in statistical surveys (Jehn at el., 2006), are not an exclusion. Due to their unique physical properties, these objects have very strong orbital evolution that is uncharacteristically to the rest of GEO population. In particular, orbital eccentricity can vary between nearly 0 and 0.7 just in half a year. So these objects are not the 'truly GEO population' members from the classical point of view; rather, they are representing an absolutely new class of the 'GEO-like' objects. Accurate motion prediction for these objects is impossible for the time intervals longer than just few days after the last observation obtained (the solar radiation pressure produces an unpredicted attitude motion of such fragments). Therefore, to study the sample of such objects, it is necessary to plan their continuous observations (as it is foreseen in current observation campaign of the Inter-Agency Space Debris Coordination Committee).

In order to obtain some data on the degree of danger of GEO fragments for operational satellites one scenario had been studied. Predicted encounters of 21 tracked fragments with a hypothetical satellite located at longitude 76E were analyzed. The 'protected space' around the satellite was bounded by 0.5 arc in longitude, 0-0.5 in inclination, and 0-0.001 in eccentricity. It was estimated that 10 of the selected fragments penetrated the protected space from 1 to 10 times per year each (39 times in 2005, 15 times in 2006, 26 times in 2007 in total), and that the most dangerous fragments are those with libration orbit having eccentricity smaller than 0.01.
4. Conclusions

The new optical cooperation, ISON, was arranged for space debris research in the GEO region. Observations of unknown GEO objects are carried out on a regular basis since 2005. The obtained data are open for scientific analysis; indeed, it was the first example of the measurement data exchange between FSU and European observers on an operational basis. Joint observation efforts resulted in valuable contribution to the knowledge of the GEO population and specific properties of unknown bright and faint objects. The orbits determined for the bright GEO objects discovered are already included in the three issues of the ESOC "Classification of Geosynchronous Objects".

The level of the faint GEO fragment research has increased significantly. The involvement of FSU telescopes allowed us to turn from statistical surveys (carried of by the AIUB team in 2001-2005) to tracking of the fragments on long time intervals. It was confirmed that there is a population of 'GEO-like' objects having a significant AMR value which results in strong perturbations of their orbits due solar radiation influence. It was found that many of the faint GEO objects have not only the unusual AMR value, but also a strange magnitude pattern. The ISON research team participates in the special IADC campaign on studying the physical properties of high AMR value objects in order to understand their nature and possible origin.

Modeling of the orbital evolutions of fragments has demonstrated that faint GEO objects on a libration orbits having eccentricity smaller than 0.01 represent a perceptible danger for operational satellites.

The capacity of ISON will increase in 2007 when the four dedicated survey 22-cm telescopes for routine observations of bright GEO and GTO objects will be put into operation, and seven telescopes of 60-cm class will be modernized to arrange a subsystem for continuous tracking of faint fragments of 15-18m brightness.

It is planned to publish the results of the faint fragment observations in a special monthly issue of the High Geocentric Orbit Space Debris Circular. These publications must give the world scientific community imagination about the status of high geocentric orbit space debris research and to provide the most recent data for each discovered object including orbital parameters, estimated standard magnitude, and estimated area-to-mass ratio value. These data can be included into existing space debris models, as well as they can be used for study of long-term orbital evolution and possible origin of the objects. The Circular will also serve as some reference document for scientists and amateurs involved in observations of these objects and in data analysis.
Acknowledgements

The authors thank our colleagues from the Switzerland and the UK for very fruitful cooperation.

The presented results would not be so complete and important without invaluable contribution of the team of the AIUB operating the ZIMLAT telescope and without discoveries and follow-up observations made by this team both in the Zimmerwald observatory and also stemming from surveys of the ESA utilizing the ESA Space Debris Telescope in Tenerife. These surveys and follow-up observations are planned, run, processed, and analyzed by the AIUB.

It was also a great pleasure to work with the highly professional team of the Observatory Sciences Ltd. which operated the PIMS optical network and which, until Jul 2005, provided a large amount of follow-up measurements for maintenance of an accurate orbital archive for bright (brighter than 15m) GEO objects in order to fill existing gaps in the real GEO population knowledge.

Also the authors would like to express appreciation to our colleagues from the Mission Analysis Office of the ESOC Ground System Engineering Department for publication in the "Classification of Geosynchronous Objects" annual of some results obtained by the ISON and its partners in this collaborative work.
References

Fig. 1. Geographic positions and diameters of telescopes collaborating with ISON in the former Soviet Union countries (observatory in Tarija, Bolivia, is outside of this map).

Fig. 2. 22-cm telescopes SR-220 in Nauchnij with IMG1001E CCD camera (left), in Pulkovo with ST-8 CCD camera (central) and in Tiraspol with ST-2000XM CCD camera (right).

Fig. 3. Distribution of magnitudes of unknown faint objects discovered.

Fig. 4. Distribution of area to mass ratio for 63 unknown faint objects.

Table 1. Observatories and telescopes of the former Soviet Union collaborating with ISON

NObservatory NameTelescopeCCDFOV, magnitude
1Nauchnij, CrAO
Crimea, Ukraine
2.6 m ZTSh* 1k 1k, 248.4' 8.4', 21
Zeiss-600*1k 1k, 2418' x 18', 17.5
64-cm AT-64**4k 4k, 92.3 2.3, 18
22-cm SR-220**1k x 1k, 24 2.8 2.8, 15
Simeiz, CrAO
Crimea,Ukraine
Zeiss-1000*2k x 2k, 1330' x 30', 19
Zeiss-600**1k 1k, 2445' x 45', 17.5
2Evpatoria, NCSFTC
Crimea, Ukraine
70-cm AZT-8* 1k 1k, 24 30' x 30', 18
3 Pulkovo, CAO RAS,
St-Petersburg, Russia
22-cm SR-220** 3k x 3k, 12 4.4 4.4, 15
65-cm refractor * 3k 3k, 12 12 12, 16.5
4 Mayaki, Odessa,
OAO, Ukraine
60-cm RC-600** 1k 1k, 2420' x 20', 17
1 1,17
5Chuguev, Kharkov,
KhAO, Ukraine
70-cm AZT-8*1k x 1k, 1530'x 30', 17.5
6 Zelenchuk, SAO RAS,
North Caucasus
Zeiss-1000* 4k x 2k, 15 15' x 7.5', 19.5
Zeiss-600** 1k 1k, 24 45' x 45', 17,5
7 Abastumani, GENAO,
Caucasus, Georgia
Zeiss-400** 3 2, 9 35' x 25', 14.5
70-cm Maxutov* 4k 4k, 9 1.5 1.5 , 18
8 Maidanak, IA UAS,
Central Asia, Uzbekistan
Zeiss-600** 1k 1k, 24 11.5' x 11.5', 17.5
1.5 AZT-22* 4k x 4k, 15 16' x 16', 20
Zeiss-600** 1k 1k, 24 45' x 45', 17,5
Kitab, IA UAS,
Central Asia, Uzbekistan
Zeiss-400** 1k 1k, 24 30' x 30', 14.5
22-cm SR-220** 1k x 1k, 24 4.4 4.4, 15
9 Mondy, ISTP RAS,
Siberia, Russia
Zeiss-600* 1k 1k, 15 7.5' x 7.5, 17
1.6 m AZT-33IK* 1k 1k, 24 5' x 5', 20
10 Ussuriysk, UApO FEB RAS,
Far East, Russia
Zeiss-400** 3k 2k, 9 35' x 25', 14.5
22-cm SR-220** 3k x 3k, 12 4.4 4.4, 15
50-cm SR-500** 4k x 4k, 9 2 x 2, 18
11 Tarija, NBAO,
Bolivia
23-cm astrograph** 1k 1k, 24 35' x 35', 14.5
Zeiss-600* 1k 1k, 24 45' x 45', 17.5
22-cm SR-220** 1k x 1k, 24 4.4 4.4, 15

Legend:
Italic type - plans of 2007
* telescope spends few nights per month for space debris observations
** telescope spends more than 50% of operative time for debris observations

Table 2. Statistics on measurements of GEO fragments collected at CCISD from ISON telescopes in October 2004 - October 2006

Observatory, telescopeQuantity of measurementsQuantity of discovered fragments
2004 2005 2006 Total
Nauchnij, AT-64 1240 1842 3562 6644 24
Nauchnij, ZTSh 0 3680 2864 6544 51
Nauchnij, Zeiss-600 0 782 2235 3017 4
Mondy, Zeiss-600 0 229 28 257 2
Maidanak, Zeiss-600 0 150 1672 1822 3
Zelenchuk, Zeiss-1000 0 258 433 691 0
Zelenchuk, Zeiss-600 0 0 11 11 0
Mayaki, RC-600 0 0 815 815 9
Evpatoria, AZT-8 0 0 272 272 1
Simeiz, Zeiss-1000 0 0 59 59 1
Terskol, Zeiss-2000 0 0 475 475 1
Ussuriysk, Zeiss-400 0 0 8 8 0
Tenerife, Zeiss-1000 0 624 1406 2068 34
Zimmerwald, ZIMLAT-1000 0 597 664 1261 3
Cyprus, 40 cm Schmidt Cassegrain 0 12 0 12 0
Total 1240 8174 14504 23956 133

2 2006.

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