Advances in Space Research,
Vol. 34 (5), 2004, pages 884891

RADAR INTERFEROMETER MEASUREMENTS OF SPACE DEBRIS USING THE EVPATORIA RT-70 TRANSMITTER

I. Molotov1, A. Konovalenko2, V. Agapov3, A. Sochilina1, B. Lipatov4, Yu. Gorshenkov5, E. Molotov6, G. Tuccari7, S. Buttaccio7, X. Liu8, J. Zhang8, X. Hong9, X. Huang9, A. Kus10, K. Borkowski10, Z. Sika11, V. Abrosimov12, A. Tsyukh12, V. Samodurov13, I. Falkovich2, L. Litvinenko2, V. Stepaniants3, A. Dementiev4, A. Antipenko4, S. Snegirev4, M. Nechaeva4, A. Volvach14, V. Saurin5, A. Pushkarev1, A. Deviatkin1, I.Guseva1, P. Sukhov15

1Central (Pulkovo) Astronomical Observatory, Pulkovskoe chaussee 65/1, 196140 St.-Petersburg, Russia
2Institute of Radio Astronomy, Chervonopraporna str. 4, 310002 Kharkiv, Ukraine
3Keldysh Institute of Applied Mathematics, Miusskaja sq. 4, 125047 Moscow, Russia
4Radiophysical Research Institute, B. Pecherskaya str. 25, 603950 N. Novgorod, Russia
5Special Research Bureau, Krasnokazarmennaya str. 14, 111250 Moscow, Russia
6Russian Institute of Space Device Engineering, Aviamotornaya str. 53, 111250, Russia
7Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
8Urumqi Astronomical Observatory, S. Beijing Road 40, 830011 Urumqi, China
9Shanghai Astronomical Observatory, Nandan road 80, 200030 Shanghai, China
10Torun Centre for Astronomy, Gagarina str. 11, 87-100 Torun, Poland
11Institute of Physical Energetics, Aizkraukles str. 21, LV-1006 Riga, Latvia
12National Control and Space Facilities Test Center, Vitino Village, 97419 Sacskiy Region, Ukraine
13Pushchino Radio Astronomy Observatory, 142290, Pushchino, Moscow region, Russia
14Crimean Astrophysical Observatory, 98409, Nauchny, Ukraine
15Odessa Astronomical Observatory, Ilpha and Petrova str. 55/1, 65122, Odessa, Ukraine


ABSTRACT

The ability of the Evpatoria RT-70 radar complex to perform research on space debris was investigated in four trial experiments during 2001-2003. The echo-signals of 25 objects at geostationary, highly elliptical and medium-altitude orbits were recorded on magnetic tapes at radio telescopes in Russia, Italy, China and Poland. The multi-antenna system configuration gives potential to supplement the classic radar data with precise angular observations using the technique of Very Long Baseline Interferometry. The first stage of such processing was fulfilled by the correlator in N. Novgorod, Russia. The cross-correlation of transmitted and received signals was obtained for the 11 objects on the Evpatoria-Bear Lakes, Evpatoria-Urumqi and Evpatoria-Noto baselines. This activity also promoted developing the optical observations of geostationary objects, conducted for the improvement of the radar target ephemerides.




INTRODUCTION

The operation of the fully steerable 70-m dish antenna in Evpatoria (Crimea of Ukraine) was resumed in 1998 under joint efforts of a number of Ukrainian and Russian institutions. This antenna was part of the former USSR Deep Space Network that was controlling all Russian spacecrafts of Martian and Venusian programs and it was stopped in 1996 after the cessation of governmental financing (because of the absence of Russian deep space missions in the near future). In the end of 1996, a joint meeting of Russian and Ukrainian scientists was arranged by the activity of the Kharkov Institute of Radio astronomy to establish the Coordinating Scientific-Technical Council. The Council proposed a concept for a radio astronomy upgrade and the use of this unique antenna. Currently RT-70 belongs to the National Control and Space Facilities Test Center (Ukrainian Space Agency) and is under scientific leadership of the Kharkov Institute of Radio Astronomy. The RT-70 is equipped with an up to 200 kW transmitter of continuous power at 5010 MHz that was used for deep space spacecraft communication and the radar researches of Mars, Venus and Mercury (Kotel’nikov et al., 1983). The Evpatoria planetary radar complex provides the linear frequency modulation of sounding signals in 512 kHz bandwidth only that limits the ability of the Evpatoria RT-70 to perform the radar investigations. Therefore, the conception of combining the classic radar and the very long baseline interferometer (VLBI) measurements (VLBR method) was proposed in 1994. The observations of echo-signals by few radio telescopes with use of technique of the VLBI provides the precise angular measurements in addition to classic radar data of range and radial velocity. At first, VLBR method was proposed for measuring the rotation variations of the planets (Alexeev et al., 2000) and his feasibility was confirmed during the experiment in June 6/8 of 1999 (Gratchev et al., 2000). Furthermore, the application of a differential VLBI technique was proposed for the observation of space debris radar echoes to determine their sky position in respect to close reference quasars (Molotov et al., 2002). Since 2001 four trial VLBI radar space debris experiments have been carried out with the Evpatoria RT-70 planetary radar and an international Low Frequency VLBI Network (Molotov et al., 1999).


BISTATIC RADAR SYSTEM WITH USE OF EVPATORIA ANTENNA

Ground-based radars are well suited to observe space debris object because of their all-weather and day-and-night performance. The Evpatoria RT-70 can not receive the echo of own radar signals from close objects as there is no possibility to quickly switch the transmitting-receiving modes. Therefore a bi-static radar system may be realized for space debris measurements only. The unique location of Evpatoria RT-70 on a distant cape of Crimea peninsula allows the radar operation without interferences of radio communications and civil aviation. On the other hand this frequency is compatible with one from traditional radio astronomy band and the most part of world radio telescopes are equipped with suitable receivers. The following antennas participated in Low Frequency VLBI Network (LFVN) project have the necessary frequency band: Noto RT-32 (Italy), Torun RT-32 (Poland), Shanghai RT-25 (China), Urumqi RT-25 (China). Moreover, Evpatoria RT-70 (Ukraine) and Bear Lakes RT-64 (Russia) were equipped with 6-cm receiver especially for radar research. These receiving antennas are at a distance of 1200 km (Bear Lakes), 1500 km (Torun), 1800 km (Noto), 4000 km (Urumqi), 7000 km (Shanghai) from transmitting Evpatoria RT-70, and therefore the resulting radar system may be used for research of high-orbit space debris. Typically, radar measurements have been used for space debris in low Earth orbits, because of the signal intensity return is inversely proportional to the fourth power of distance. But the large diameter of Evpatoria antenna and high power of the transmitter theoretically provide the possibility to see the cm-sized space debris fragment at the geostationary orbit (GEO) (Zaitsev et al., 2001). The diameter of the antenna beam is about 40 km at GEO. Therefore the potential of Evpatoria RT-70 => LFVN radar system promises an interesting opportunity to search for small-sized space debris at GEO and highly elliptic orbits (HEO).

The GEO region represents a very interesting field for research due its dense satellite population and importance for human civilization. The DISCOS database contains the data on 934 GEO-objects and more than 240 objects on HEO orbits, which regularly cross the GEO area. The observations of ESA space debris telescope at the Teide Observatory on Tenerife showed an unexpected large population of uncatalogued fragments with sizes from 10 cm to 1 m at both GEO and HEO (Schildknecht et al., 2001). The presence of a large quantity of unobservable small objects is indirectly confirmed by analysis of long-term evolution of the 350 uncontrolled GEO-objects. More than 100 objects had unexplained changes of drift rate from 0.0005 to 0.03 degree/day and it may be interpreted as collisions with invisible little fragments (Sochilina et al., 2001). Therefore the involvement of the Evpatoria RT-70 planetary radar is very important for searching debris in GEO.

Non of the LFVN antenna has the special radar equipment for echo-signal processing. Therefore, it was proposed to use existing standard VLBI recording terminals (base band converter, 1-bit sampler, S2 or Mk-2 formatter, videocassette recorders) to register an echo-signal in 2 MHz frequency bandwidth on magnetic tapes for further analysis at VLBI data processing center. Bear Lakes Mk-2 terminal can record also the echo-signal intensity (the same 2 MHz band signals after quadratic detector) in digital form (10 binary bit with period of 16 milliseconds). The analysis of recorded signal intensity can easily fix the period of object rotation in the case of periodic repeating peaks. Two VLBI data processing centers agreed to correlate the VLBI radar observations results: NIRFI-3 correlator of Mk-2 format of Radio Physical Research Institute in N. Novgorod, Russia (Antipenko et al., 2001) and ASC-1 correlator of S2 format of P.N. Lebedev Physical Institute (Belousov et al., 2001). Such use of VLBI recording terminals and correlation centers gives the opportunity to add the classic radar data with specific VLBI measurements. The main goal of the study described in this paper was to clear the possibility of the VLBI technique application for the space debris radar echoes. It was expected that the cross-correlation of the transmitted and received signals can measure the Doppler shift with a potential hardware error of 0.003 Hz and the difference between the Doppler shifts at two VLBI antennas with 0.001 Hz. In principle, the VLBI measuring of radio signal angular direction can determine the sky position of an object with a precision of 0.05” (Dementiev et al., 2001). The differential VLBI technique (determination of object coordinates with respect to close reference quasars) potentially can provide the precision of angular measurements from 0.01” to 0.001” (Alexeev et al., 1989) because in the such technique some systematic errors can be accident. And at last, the standard VLBI imaging procedure can reconstruct a detailed map of the investigated object (Margot et al., 1999) with spatial resolution which is proportional to the length of interferometer baseline and the distance to the investigated object.


DIFFERENTIAL INTERFEROMETER RADAR TECHNIQUE

The VLBI technique implies the joint observations of the radio telescope array of selected radio sources in the desired frequency band under a common schedule. In each radio telescope, the radio signals are received with low noise receiver and transformed into an intermediate frequency. Then base band converter filters the necessary frequency bandwidth and transforms the signals into video frequencies, which then are sampled with 1- or 2-bit quantization, formatted in any standard VLBI format (Mk-4, S2, K-4, Mk-2) and recorded on magnetic tapes together with precise clock by VLBI terminal. All frequency transformations are connected with H-maser standard. The tapes from all radio telescopes of VLBI array are collected at data processing center when the data are cross-correlated to produce a cross-correlation "fringe pattern". This fringe pattern can then be analyzed to produce a result ranging from an image of a distant astronomical object to the precise location of a nearby terrestrial or extra-terrestrial radio emitter.

The differential VLBI technique is widely used for measuring spacecraft trajectories and position of pulsars with an accuracy up to 0,001". This procedure allows to link the sky position of object with the position of close quasars on the celestial sphere (the angular distance between close quasar and observed object must be 5o – 10o). During the experiment, the radio telescopes alternately observe the object and reference quasar. Each experiment contains the few cycles: 15 minutes of object observations and 10 minutes of observations of reference quasar (few close ICRF quasars are selected along trajectory of object in order to receive few points of measurements). The recorded pairs (object and reference quasar signals) are processed at the correlation center to determine the relative fringe rate (the recording of each signal from all telescopes are processed independently and the resulting fringe rates are compared). In the case of VLBI radar measuring, the ground radar “illuminates” the space debris fragments. Therefore the radio telescopes observe the echo-signals instead of natural or artificial radio sources. Unlike the classic radar procedure, the transmitter radiates the unmodulated sine wave signals. The copy of the transmitted signals is recorded on magnetic tapes for use in further processing. Contrary to standard VLBI technique, the echo-signals are very narrow-band and have additional Doppler shift contribution due to object’s orbital motion. The echo-signals are recorded on magnetic tapes at 2 MHz bandwidth, the limits of that are fixed by taking into account the average Doppler shift for the period of observations. The radar echoes are the near-field signals in comparison with natural radio sources (quasars, stars, masers) and standard VLBI correlation software can’t be used.

The first stage of processing includes the auto-correlation of recorded tapes to detect the echo-signals from each object on each antenna. The second stage includes the cross-correlation of transmitted signals and received radar echoes for each baseline “transmitting antenna – receiving antenna” to determine the degree of signal coherency and to measure the Doppler shift of object, if coherency was acceptable. The third stage is the cross-correlation of radar echoes recorded by different antennas to search the VLBI fringes and to measure the fringe rate in the case of success. Then the reference quasar signals are also cross-correlated and the relative (echo-quasar) fringe rate value is measured. During processing, the signal delay-time dependence in the form of 3rd degree polynomial is calculated in respect to a preliminary trajectory model of object, coordinates of VLBI points and time of cycle. This calculation takes into consideration the near-field effect associated with the movement of the object with respect to the center and rotation of the Earth. Such polynomial is used for computation of shift-time dependences, which are introduced during correlation processing in radar echo signals received at each VLBI point of interferometer baseline. These procedures allow equivalently "to stop" the space debris object and Earth in the time of beginning of the processed observation cycle (moment of signal transmitting from Evpatoria RT-70) and accumulate the energy of the signal in the necessary time period. The Doppler shifts and positions of the space debris object measured with highest precision will allow to considerably improve an orbit determination based on optical observations.


RADAR INTERFEROMETER OBSERVATIONS AND RESULTS

First Experiment

The capacity of Evpatoria=>LFVN bi-static radar system to perform the space debris measurements was tested in four trial experiments. The pioneer attempt (VLBR01.1 experiment) was arranged in May 23-29 of 2001 with participation of Bear Lakes RT-64, Noto RT-32, Torun RT-32, Shanghai RT-25, Urumqi RT-25, Svetloe RT-32 (near St.-Petersburg, Russia) and MERLIN radio interferometer system (England). The GEO-targets for the first experiment were selected so as to satisfy the following requirements: non-functional (to avoid possible distortion of operational satellites), have an inclination as small as possible (i.e. small motion in elevation) and relatively small longitudinal motion (i.e. small motion in azimuth angle), have the large size as possible (to maximize the levels of reflected signal), be located so that all participants (in England, Poland, Italy, Russia, China) have clear visibility zones, have good known orbits (accuracy of orbit should be enough for tracking by Evpatoria RT-70 and Bear Lakes RT-64 having the 3.5’ beam width). The additional optical observations were arranged to improve their orbits. The following 7 targets were chosen: 1982-044F Proton 4th stage (Block DM No.28L), 1984-063A Raduga 15, 1988-095A Raduga 22, 1990-061D Proton 4th stage (Block DM-2 No.24L), 1982-044A Cosmos-1366, 1988-066A Kosmos-1961, 1991-010A Cosmos-2133. The Evpatoria RT-70 can successfully track all 7 objects, the radiated power at 5010.024 MHz was about 120 kW, and strong echoes were fixed at MERLIN and Bear Lakes. The further auto-correlation processing displayed the echoes on recorded tapes of Svetloe, Urumqi and Noto radio telescopes. The recording of echo-signals intensity was made for 1990-061D and 1988-95A objects (Figures 1, 2). The structure of echo-signals demonstrates the uncontrolled axial rotation of objects and allows to estimate the main period of their proper rotation as 5.93 s and 21.9 s respectively.



Fig. 1. The 16.67 s recording of echo intensity of the GEO-object 1990-061A, Bear Lakes RT-64, 27.05.01, start in 23:44:42 UT, main period of rotation is 5.93 s


Fig. 2. The 166.35 s recording of echo intensity of the GEO-object 1988-95A, Bear Lakes RT-64, 28.05.01, start in 01:02:07 UT, main period of rotation is 21.9 s.


The first successful attempt of correlation processing of GEO-object echo-signals was made by NIRFI-3 Mk-2 processor in N. Novgorod. The cross-correlation of the transmitted signals from Evpatoria RT-70 and received in Bear Lakes RT-64 and Urumqi RT-25 was made for 1990-061D Proton 4th stage. The precise Doppler shift was not measured due to the limited frequency resolution of the correlator.


Second Experiment

The second space debris VLBR01.2 experiment was arranged in December 14-19, 2001. The goal of this VLBI radar observations was to check the capability of Evpatoria=>LFVN radar system to observe GEO-object with size less 1 m and space debris objects at HEO, and to test the performance at 5.01 GHz of the new Russian 64-m radio telescope near Kalyazin. The observing program included also exploded GEO-objects and objects having unexplained change of drift rate. Moreover, a first attempt of beam park experiment to detect small-sized unknown GEO-fragments was arranged between Evpatoria and Bear Lakes. The radiated power at 5010.024 MHz was about 65 kW. The receiving telescope array consisted of Bear Lakes RT-64, Kalyazin RT-64, Shanghai RT-25 and Urumqi RT-25. The processing of recorded tapes displayed the echo signals of 6 objects – 2 for HEO-objects: 1998-027D Molniya-M 4th stage and 1977-021A Molniya-1 satellite, and 4 for GEO-objects: 1968-081E Transtage upper stage (exploded on Feb 21, 1992) and its fragment 1968-081H, 1977-092A Ekran 2 and 1980-104A Ekran 6.


Third Experiment

The third VLBR02.1 experiment was carried out in July 23-29, 2002. This was the first attempt to track objects in medium-height orbits. The main technical goal was the testing of specialized real-time Internet interface designed in Noto VLBI station (see more in Outlook and Tuccari et al., 2002). The observing program contained also GEO and HEO objects. The second attempt of the beam park experiment to detect small-sized unknown GEO-fragments was conducted between Evpatoria and Noto. The radiated power at 5010.024 MHz was about 65 kW. The receiving telescope array consisted of Bear Lakes RT-64, Kalyazin RT-64, Noto RT-32, Shanghai RT-25 and Urumqi RT-25. The processing of recorded tapes displayed the echo signals of 7 objects: 1989-001C Cosmos-1989 on a near-circular 19150 km height orbit, 1999-033D Proton 4th stage (Block DM3 No.8L) on HEO and 5 GEO-objects: 1975-097A Cosmos-775, 1981-069A Raduga 9, 1982-044A Cosmos-1366, 1988-018B Telecom-1C and 1991-054D IUS-15 SRM-2 (Orbus 6E). The recording of echo-signals intensity was made for two GEO and one HEO object (1981-069A, 1982-044A, 1999-033D) and the rotation periods were estimated as 61.09 s for the GEO-object 1981-069A (Figure 3) and 4.95 s for the HEO-object 1999-033D (Figure 4).


Fig. 3. The 2.4 minute recording of echo intensity of the GEO-object 1981-069A, Bear Lakes RT-64, 25.07.02, start in 11:35 UT, main period of rotation is 61.09 s.



The second attempt of correlation processing was made in N. Novgorod after improving the frequency resolution of the NIRFI-3 correlator. The cross-correlation of transmitted signals and radar echoes which were received in Bear Lakes RT-64 and Noto RT-32 was made for the GEO object 1991-054D with frequency resolution 0.03 Hz (Figures 5, 6). This allowed to precisely measure the received sky frequency of echoes (correspondingly 5010023977.415 Hz and 5010023974.721 Hz) and to determine the Doppler shift (correspondingly -22.585 Hz and -25.279 Hz) in both VLBI points.

Fig. 4. The 1.2 minute recording of echo intensity of the HEO-object 1999-033D, Bear Lakes RT-64, 23.07.02, start in 15:55 UT, main period of rotation is 4.95 s.



Fig. 5. Spectrum of interference signal on baseline Evpatoria (sounding signal) – Noto (radar echo) for the GEO object 1991-054D, 25.07.02, 13:20 UT, 33.24 s integration time, 0.03 Hz frequency resolution, Doppler shift -25.279 Hz .


Fig. 6. Spectrum of interference signal on baseline Evpatoria (sounding signal) – Bear Lakes (radar echo) for the GEO object 1991-054D, 25.07.02, 13:20 UT, 33.24 s integration time, 0.03 Hz frequency resolution, Doppler shift -22.585 Hz.



17 values of Doppler shifts were obtained for the GEO-object 1982-044A, 12 in Bear Lakes RT-64 (Figure 7) and 5 in Noto RT-32 (Figure 8) to check the consistency of the measurements. Figure 17 shows the Bear Lakes measurements acing a polynomial of 3rd degree. The mean-root-square error is 0.096 Hz (corresponding to 3 mm/s rate), that is three times worse than apparatus mistake (1 mm/s rate). This may be explained by the rotation of the object.

Fig. 7. The Doppler shifts of the GEO-object 1982-044A radar echo depending on time and its approximation by smoothing polynomial, 25.07.02, 12:43 – 12:49 UT, Evpatoria – Bear Lakes baseline.



Fig. 8. The Doppler shifts of the GEO-object 1982-044A radar echo depending on time and its approximation by smoothing linear function, 25.07.02, 12:44 – 12:46 UT, Evpatoria – Noto baseline.



The post-processing of the data on the GEO-object 1982-044A shows that the measured Doppler shifts are in good agreement with the orbit reconstructed based on optical observations. There is a constant difference for both VLBI points (Bear Lakes and Noto) of about 7 cm/s in range-rate. After mutual processing of optical and radar data the difference between Doppler measurements and new model orbit was about 1 cm/s only.


Fourth Experiment

The fourth VLBR03.1 experiment was carried out in July 23-29, 2003. The observing program included GEO, HEO and medium-height orbit objects. The third attempt of the beam park experiment to detect small-sized unknown GEO-fragments was conducted between Evpatoria, Bear Lakes, Noto and Urumqi and first attempt of the beam park for low orbit between Evpatoria and Simeiz. The radiated power at 5010.024 MHz was about 40 kW. The receiving telescope array consisted of Bear Lakes RT-64, Noto RT-32, Urumqi RT-25 and Simeiz RT-25. The processing of recorded tapes displayed the echo signals of 10 objects: 1976-107A Ekran 1, 1977-092A Ekran 2 (exploded in 1978), 1979-105A Gorizont 3, 1981-069A Raduga 9, 1982-044A Cosmos-1366, 1989-001C Cosmos-1989, 1989-081A Gorizont 19, 1994-056С LAPS AKM, 1998-029B Centaur TC-18, 1999-033D Proton 4th stage (Block DM3 No.8L). The Doppler shifts were measured for all objects on the Evpatoria-Bear Lakes and Evpatoria-Urumqi baselines. The recording of echo-signals intensity was made for the 5 objects 1976-107A, 1979-105A, 1981-069A, 1982-044A, 1999-033D and their rotation periods were estimated respectively as 166.75 s, 82.442 s, 83.539 s, 189.833 s, 5.772 s (see Figure 9 for an example).



Fig. 9. The 6 minute recording of echo intensity of the GEO object 1981-069A, Bear Lakes RT-64, 28.07.03, start in 19:47:10 UT, main period of rotation is 83.539 s.



Fig. 10. The recording of echo intensity of the GEO object 1981-069A with high temporary resolution



In the next processing stage, it is supposed to use the recording of the echo intensity with high temporary resolution (see Figure 10) to estimate the reflecting area size of the space debris objects.


OUTLOOK

It is expected that regular VLBI radar space debris investigations will be continued with the support of grants INTAS 2001-0669, INTAS-IA-2001-02, RFBR 02-02-17568 and RFBR 03-02-31013 including development of the near real-time VLBI radar technique. The Noto RT-32, Bear Lakes RT-64 and Urumqi RT-25 were equipped with specialized real-time Internet interfaces designed in Noto VLBI station. This allows to transfer the radar echoes through Internet from the radio telescopes to the near real-time correlator in Noto. A near real-time system. can provide quickly the results of radar observations. The model of a near real system (first two samples of VLBR terminal and software correlator) was successfully tested with Noto RT-32 and Bear Lakes RT-64 in VLBR03.1experiment in July 2003. The Figures 10, 11 demonstrate the first work result of the VLBR terminals and real-time software correlator.


Fig. 11. Echo of the GEO-object 1982-044A received at Bear Lakes RT-64, translated and processed at Noto with use of real-time Internet system. Autocorrelation spectrum of 1 MHz band.



Fig. 12. Echo of the GEO-object 1982-044A received at Noto RT-32 translated and processed at Noto with use of real-time Internet system. Autocorrelation spectrum of 1 MHz band.



With the INTAS 2001-0669 project VLBI radar observations of the new radio astronomy observatory near Ventspils, Latvia within 32-m antenna will be supported (Shmeld et al., 2002). It is planned to equip this radio telescope with a 6-cm radio receiver and a new reference frequency standard. The promotion of optical observations in former Soviet Union countries also is considered under this grant. As first step, coordinated optical observations of space debris in GEO are carried out in Pulkovo (10-cm and 32-cm CCD-telescopes), Goloseevo (double 40-cm astrograph 8ox8o, photo plates), Almaty (70-cm AZT-8 and 50-cm AZT-28, TV tubes), Mondy (50-cm CCD-telescope AZT-14), Nauchnyi (22-cm SF-220, 5ox5o, photo tape; 64-cm CCD-telescope AT-64), Mayaki (30-cm telescope, TV tube). The links with other observatories are under development. A catalogue of GEO objects is under preparation.


CONCLUSIONS

The new international program of the space debris investigations with facilities of the former Soviet Union countries is in development. The powerful transmitter of the Evpatoria RT-70 has been active in space debris research since 2001. The radar echoes are received with an international array of radio telescopes. Three trial experiments confirmed that the bi-static Evpatoria=>LFVN radar system is able to investigate the space debris objects at GEO, HEO and medium-height orbits. Both method and equipment for a new radar interferometry technique for precise Doppler shift measurements were developed. As first results, the echoes of 25 space debris objects were detected with use of the Bear Lakes RT-64, Noto RT-32, Urumqi RT-25, Kalyazin RT-64 and Svetloe RT-32, and the Doppler shifts of 11 objects were measured with precision of 0.001 Hz on the Evpatoria-Bear Lakes, Evpatoria-Noto and Evpatoria-Urumqi baselines. The Internet interfaces and software correlator for the near real-time VLBI radar researches were successfully tested. Coordinated optical observations from Pulkovo, Goloseevo, Almaty, Mondy, Simeiz and Mayaki were carried out in support of the radar investigation program.


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E-mail: molotov@kiam1.rssi.ru
Manuscript received 30 November 2002; revised 14 March 2003; accepted 30 September 2003.