¹ Central (Pulkovo) Astronomical Observatory, Pulkovskoe chaussee 65/1, 196140 St.-Petersburg, Russia
² Keldysh Institute of Applied Mathematics, Miusskaja sq. 4, 125047 Moscow, Russia
³ Special Research Bureau, Krasnokazarmennaya str. 14, 111250 Moscow, Russia
⁴ Radiophysical Research Institute, B. Pecherskaya str. 25, 603950 N. Novgorod, Russia
⁵ Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
⁶ Crimean Astrophysical Observatory, 98409, RT-22 Simeiz, Ukraine

Bear Lakes Radio Astronomy Station (BLRAS) is the IVS affiliated organization since 2003. During 2004, the S/X band receivers were installed and tested with RT-64, new CH1-75A H-masers were integrated in time and frequency service system. The repairing the building and rooms, painting the antenna were continued, the same as producing the 128 MHz 8-channel BBC. BLRAS participated in three VLBI radar experiments of LFVN using Mk-2 and NRTV recording terminals. BLRAS coordinates the LFVN activities and therefore includes not only the network station staff, but also operation, correlator, analyzing and technology development groups. During 2005 it is planned to finish first half of 128 MHz BBC to participate in S2 geodetic VLBI at 64 MHz bandwidth. This work was supported by INTAS-01-0669, RFBR 02-02-17568 and RFBR 02-02-39023 grants.

The 64 m dish antenna near Moscow, Russia was erected by Special Research Bureau (SRB) of Moscow Power Engineering Institute in 1979, put into operation in 1983. It has a quasi-parabolic axially symmetric Gregory mirror system with subreflector of 6-m diameter and multi-band feed-horn system. The dish is equipped with a system for the phase compensation of gravitational deformation by means of a programmed subreflector movement. Rotation angles: +220 degrees in azimuth, 1-89 degrees in elevation; guidance velocities: from 1.5 arcsec/s to 0.75 arcmin/s along two coordinates and object tracking accuracy about 15 arcsec. An effective area was about 2000 square meters at wavelength 18 cm with the possibility in principle for the main mirror to operate up to 1.35 cm.

It was a part of the Russian Deep Space Tracking Network [1] which controlled all Russian deep space missions of Martian and Venusian programs and received the telemetry information from these spacecraft (i.e. it received the signals with Venusian surface panorama), participated in differential VLBI measurements of the Venus Atmosphere Dynamics Balloons in VEGA Project [2]. Some part of antenna's time was always spent for radio astronomy research under activity of few NIS scientific institutes. As part of radio interferometer "Orion", Bear Lakes participated in differential VLBI measurements of deep space and high-apogee mission spacecraft trajectories [3], fulfilled a series of VLBI experiments with USA DSN antennas [4], participated in a series of geodetic NIS VLBI observations and had episodic collaboration with European and Global VLBI Network with Mark II recording terminal [5]. In fact, Bear Lakes RT-64 was the informal center of collective use for many Russian scientific institutes. But lack of modern radio astronomy equipment due to absence of specialized financing for this goal was limiting this activity. Nevertheless, Bear Lakes always demonstrated excellent and stable performances in the time of VLBI experiments (best of all other NIS antennas). The observations were carried out at 18 cm wavelength mostly. In 1996, Bear Lakes RT-64 joined the project of Low Frequency VLBI Network (LFVN) that has the purpose to arrange international VLBI cooperation with participation of former Soviet Union antennas [6].

Figure 1.
Left side: Bear Lakes RT-64 near Moscow, Russia; right side: Antenna surface with holography reference antenna.

The trial observations with Canadian S2 recording system (up to 128 Mbit/sec) were arranged between Bear Lakes and Tidbinbilla in June 1996 with a S2 baseline of 11538 km. But the RT-64 was equipped with S2 terminal on permanent basis in 1998 only. The base band converter (single channel of 2, 4 or 8 MHz) and sampler (S2 interface) were produced. The Bear Lakes RT-64 participated in five S2 observation sessions under LFVN project and a few VSOP experiments at 18-cm wavelength in 1998-2000 [7].

In 2000, the 6-cm cooled receiver was installed at Bear Lakes RT-64 under LFVN program of VLBI radar searching for the near Earth asteroids, the Earth group planets and space debris. RT-64 participated in four VLBR sessions in 2001-2003 [8].

In 2002, September 26, the agreement between Special Research Bureau of Moscow Power Engineering Institute and Central Astronomical Observatory at Pulkovo (CAO) of Russian Academy of Sciences was signed to establish the Bear Lakes Radio Astronomy Station (BLRAS). Since this time, all radio astronomical works at Bear Lakes RT-64 are carried out under BLRAS activities. BLRAS is the IVS affiliated organization from 2003.

Joint team of SRB, CAO and Radiophysical Research Institute (RRI) provides the BLRAS operations. The BLRAS staff consists of collaborators from all these three organizations. In common, SRB is responsible for the antenna pointing and maintenance, frequency and time service, radio receiver operating, antenna cable network and Internet and phone lines. CAO is responsible for the coordinating of BLRAS activities, providing the necessary financial support and maintaining the NRTV and S2 recording terminals. RRI is responsible for the technical elaborations and VLBI experiment performing.

Figure 2.
BLRAS VLBI team, from left to right, N. Sukorkin (Evpatoria RT-70 group), A. Pushkarev (Evpatoria RT-70 group), A. Dementiev, M. Nechaeva, N. Dugin (head of RRI VLBI laboratory), V. Samodurov (deputy director of Puschino radio astronomy observatory), I. Shmeld (member of Ventspils RT-32 VLBI group), A. Antipenko.
April 2004, tests of S/X receivers.

The regular BRLAS staff included Igor Molotov (head of BLRAS), Valeriy Saurin (technical director, his group provides the antenna pointing and maintenance), Yuriy Gorshenkov (VLBI-friend, his group provides the time and frequency service, radio receiver maintaining, cable network, links etc.), Alexander Antipenko (BBC and Mk-2 maintaining, VLBI experiment performing), Alexander Dementiev (his group is responsible for the elaboration of new apparatuses), Vladimir Jazykov (NRTV and S2 terminal maintaining), Boris Sapojnikov (antenna performance measuring), Ivan Puchinin (radio metric measurements), Maria Nechaeva (experiment scheduling), Alexander Pushkarev (experiment post-processing), Vladimir Titenko (preparing the radar experiment programs). Also another persons of SRB and RRI are involved for the installing and testing the new equipment.

The program of the Bear Lakes VLBI site modernization was started in 2003 [9]. Two new Russian CH1-75A H-masers were purchased in 2004 under grant of Russian Ministry of Education and Science, two old BLRAS H-masers were repaired and adjusted in GNIPI, N. Novgorod. Thunderbolt GPS Disciplined Clock with time precision down to 20 ns was purchased and incorporated in time and frequency service of antenna site. Internet access was organized by optical cable connection to the antenna building. The maximum speed is 500 Mbit/s (current 100 Mbit/s due to interface card). The near real time VLBI (NRTV) terminal [10] was installed and tested in trial e-VLBI experiments. The S/X band receivers and feedhorn parts were produced, installed at RT-64 and tested in April 2004. The 49 cm receiver is already in BLRAS and will be installed and tested with RT-64 in spring 2005. The 18-cm receiver local oscillator was repaired. The 6-cm band receiver was modernized - new low noise amplifier, local oscillator and apparatus of secondary frequency transformation were produced and tested. Producing the 128 MHz 8-channel base band converter was continued and must be finished in 2005. The repairing the antenna building and rooms, painting of antenna constructions and mirrors was started in 2003 and will be ended in summer 2005.

The VLBI activities of BLRAS were arranged under Low Frequency VLBI Network Project (LFVN) [6]. The observations at 18 cm wavelength that were carried out in January 2003, after long interruption (previous 18-cm experiment was in December of 2000), fixed the strong increasing of interferences in this frequency band that may be explained by close erecting of tower for mobile telephone connection "Combelga". There are no serious interferences at 6 cm wavelength, in that new VLBI radar experiments were performed in July 2003, June 2004, July 2004 and September-October 2004.

In fact, BLRAS coordinates the LFVN activities and therefore includes the operation group for planning and scheduling LFVN experiments, network station group for performing the VLBI observations with Bear Lakes RT-64 and supporting VLBI observations with Evpatoria RT-70, correlator group that maintaining the operation NIRFI-3 Mk-2 correlator in N. Novgorod and elaborating new NRTV correlator, analyzing group for post-processing the LFVN experiments and technology development group for elaborating the new VLBI apparatuses for Bear Lakes and other LFVN members.

LFVN project was started in 1997 [6] having the purpose to arrange the international VLBI cooperation with participation of former Soviet Union radio telescopes. At first stages, LFVN was developing dynamically and successfully: 13 antennas at different countries were equipped with new receiving-recording radio astronomy apparatuses, 20 VLBI test and scientific experiments were carried out using various combinations of radio telescopes in Canada, China, England, India, Italy, Japan, Latvia, Poland, Russia, South Africa, Ukraine and USA. Currently, LFVN collaborates with Bear Lakes RT-64, Pushchino RT-22, Zimenki RT-15, St. Pustyn RT-14 (Russia), Evpatoria RT-70 and Simeiz RT-22 (Ukraine), Noto RT-32 (Italy), Urumqi RT-25 and Ventspils RT-32 (Latvia). It operates at 92 m, 18 cm and 6 cm wavelengths using Mk-2, NRTV recording terminalsfor investigations of solar wind, solar spikes, AGN, OH-masers, active stars and radar research of Earth group planets, close asteroids and space debris objects. LFVN results were published in more than 100 papers in open scientific literature. Using the S2 VLBI recorder system was interrupted because of stopping the collaboration with Penticton S2 correlator of DRAO in Canada.

During 2003-2004, the program of the Bear Lakes VLBI site modernization was fulfilled. The 49 cm receivers and combined feedhorns were produced and GPS-receivers were purchased for Zimenki RT-15 and St. Pustyn RT-14, also new frequency standard was purchased for St. Pustyn and S2 recording terminal was installed under grants of Russian Foundation for Basic Research and Russian Ministry of Education and Science. The 6 cm receiver mixer and apparatus of secondary frequency transformation were produced for Ventspils RT-32. The NRTV recording terminals were produced, installed and tested in Bear Lakes, Noto, Urumqi, Evaptoria and Simeiz. Five VLBI experiments were arranged, the recordings were partially processed at NIRFI-3 correlator of Mk-2 format in N. Novgorod, Russia and NRTV correlator in Noto, Italy.

The echoes of about 50 space objects with sizes of 0.5 - 100 m and also Mars, Venus and Moon were detected on magnetic tapes or PC-disks at Bear Lakes RT-64, Noto RT-32, Urumqi RT-25 and Simeiz RT-22 and then analyzed. The rows of precise Doppler shifts were measured at three receiving points, the rotation periods and sizes of some objects were estimated. Recently the VLBI fringe rate was measured at three baselines for echoes of few GEO objects that can allow to obtain the angular coordinates with accuracy up to 0.05" [11].

The time dependence of spectral maximum of echo from Raduga-9 on baseline Evpatoria - Bear Lakes (Fig. 8, left side) shows the period of rotation as 83 s, while spectrum Evpatoria-Urumqi demonstrates two time longer period. This means that Raduga 9 has symmetric elements (i.e. solar batteries) that are visible from Bear Lakes and Urumqi under different angles. Analysis of time evolution of spectral maximums of echo from Cosmos-1366 on Bear Lakes - Noto - Urumqi baselines (Fig. 8, right side) allows to get new information about proper movement of investigated object. There are the shifts of cross-spectrum maximums at different baselines: - 3.35 s for Bear Lakes - Noto, +1.65 s for Bear Lakes-Urumqi and 5.5 s for Noto-Urumqi baselines. Accordingly Bear Lakes site, the echo signals ahead in Noto at 2.15 s and delayed in Urumqi at 5 s. It may be explained that scattering pattern of Cosmos-1366 is narrow (few degrees) and radiation maximum successively passed the receiving antennas during rotation. This fact allows to evaluate the direction of object rotation axis.

During 2005, it is planned to finish the half set of BBC for Bear Lakes to have the 64 MHz bandwidth for performing the geodetic VLBI observations with Canadian S2 system recording terminal. The development of the differential VLBI radar method for the astrometry measurements of the Solar system bodies will be continued. The next such observations are planned for the summer. Also there is plan to arrange trial experiments on differential VLBI measurement of European interplanetary spacecraft position in autumn. The works on the creation of new LFVN correlator for e-VLBI will be started. It is supposed to realize the divided scheme when part of processing will be performed at radio telescopes and only few data will be transferred to central processor using Internet.

This work was supported by INTAS-01-0669, RFBR 02-02-17568 and RFBR 02-02-39023 grants.

1. Molotov, E. P. Ground radio technique systems for control of spacecrafts, Book, M.: FIZMATLIT, Moscow, Russia, 1-256, 2004 (in Russian).
2. Sagdeev, R. Z. et al. Differential VLBI Measurements of the VEGA Balloon Trajectories, Soviet Astronomy Letters, Vol. 14, no. 2, 154, 1988.
3. Alexeev, V. A. et al. Long baseline narrow-band radio interferometry for space navigation. Interplanetary spacecrafts; measurements of coordinates of AMS Vega. Kosmicheskiye Issledovaniya, Vol. 27, Is. 3, 447-453, 1989 (in Russian).
4. Molotov, I. et al. VLBI activity of ASC on Russian Deep Space Tracking Network. Proceedings of the Technical Workshop for APT and APSG 1996, Kashima, Japan, Dec. 10-13, 1996, pp 284-288.
5. Britzen, S. et al. The radio structure of 1803+784. New Astronomy Reviews, Vol. 43, Nos. 8-10, 1999, pp. 751-755.
6. Molotov, I. E. et al. Low Frequency VLBI Project. The Universe at Low Radio Frequencies, Proceedings of IAU Symposium 199, 30 Nov. - 4 Dec. 1999, Pune, India. Eds. A. Pramesh Rao, G. Swarup, and Gopal-Krishna, 2002, p. 492-493.
7. Pushkarev, A. B. et al. Quasi-Simultaneous VLBI and RATAN-600 Observations of Active Galactic Nuclei. Astronomy Reports, Vol. 48, Issue 11, 2004, p. 900-908.
8. Molotov, I. et al. Radar interferometer measurements of space debris using the Evpatoria RT-70 transmitter. Advances in Space Research, Vol. 34, Issue 5, 2004, pp. 884-891.
9. Molotov, I. Two-year program to upgrade Bear Lakes RT-64 for EVN membership. Proceedings of the 6th European VLBI Network Symposium, Ros, E., Porcas, R. W., Lobanov, A. P., and Zensus, J. A. (eds.), June 25-28, 2002, Bonn, Germany, pp. 21, 22.
10. Tuccari, G. et al. A Near Real Time e-Radar/VLBI Network. IVS 2004 General Meeting Proceedings, p. 225-228.
11. Molotov, I. E. Experiments on the differential VLBI measurements with the former Russian deep space network. Submitted in the proceedings of the 18ISSFD Symposium, Munich, October 11-15, Germany, 2004, 5 pages.

Размещен 28 октября 2006.