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Okean

Although the National Space Agency of Ukraine was formed in March, 1992, and the country already had expertise in developing full satellite and launch vehicle systems, the country was slow in preparing for its first official national satellite. This situation should be remedied in 1995 with the launch of the Sich-1 spacecraft, aka Okean-O. Based on the oceanographic series of spacecraft developed by the Yuzhnoye Scientific Production Association under the USSR regime, Sich-1 is reportedly the last of its kind and will be followed by more advanced Earth observation satellites (References 731-734).

Each Okean spacecraft has a mass of a little more than 1,900 kg, with a payload capacity of 550 kg and is launched from the Plesetsk Cosmodrome by the Tsyklon-3 booster, also made by Yuzhnoye NPO. The spacecraft bus is a three-segmented, vertically oriented cylinder, three meters tall with a base diameter of 1.4 m and an upper diameter of 0.8 m. Okean's primary structure is pressurized and maintained at normal temperatures to protect the support system and payload electronics housed within. Two small, rotatable solar arrays (1.6 m wide and 2.0 m tall) provide a modest 110-270 W average daily power to the payload. Stabilization is partially provided by a gravity-gradient boom extended from the top of the satellite. At the bottom, four large panels (1.0 m wide and 2.9 m long), attached at 90 degrees intervals, support a number of payload receivers and transmitters. An arrow, 11-m-long radar antenna is fixed to the base of one panel.

Okean spacecraft transmit data in realtime on 137.400 MHz using APT formats similar to that employed by Meteor satellites with a scan rate of 4 lines per second. Data is also stored and retransmitted on 466.5 MHz to the three principal data reception and processing centersat Moscow, Novosibirsk, and Khabarovsk. The APT images may be sent in one of four formats: (1) one low resolution scanner, (2)side-looking radar and microwave scanning radiometer, (3) side-looking radar alone, and (4)a combination of radar, microwave, and visible images. For instance, images of the Middle East region have a size of 195 mm by 290 mm with a scanning density of 7.6 lines per mm and at least 12 gray levels (References 735-740).

The major Okean payload is the real-aperture, side-looking RLS-BO radar operating with a vertically polarized 9.5 GHz frequency. This instrument, developed by the Radio Engineering and Electronics Institute (IRE) in Kharkov, provides not only surface characteristics of land, sea, and ice but also near-surface winds Reds and sub-surface features. The last has proved to be exceptionally effective in determining ice thickness in the polar regions as an aid to naval navigation.

From its orbital altitude of 635 km by 665 km at an inclination of 82.5 degrees, an Okean satellite employs both nadir-centered and off-nadir swaths. The MSU-M and MSU-S sweeps are centered about the sub-satellite point, but theRLS-BO and RM-08 swaths are displaced to the left of the ground track. The boresight of the MSU-M can be shifted up to 30 degrees along the direction of the flight path. In part, due to power limitations, the MSU-M and RM-08 cannot be operated for more than 30 minutes at a time, and the RLS-BO is restricted to 10-minute sessions.

Okean satellites also serve as the central node in the Condor system which collects environmental data from small, remote stations on land, water, or ice. These stations, designated Condor-1, are interrogated by Okean satellites at 460.03 MHz and then transmit their data at 1553.4 MHz during a 4-12 second contact. Okean, also known as the Condor-2 node, then relays the data to special Condor-3 processing stations at 460.03 MHz. Okean satellites can interrogate Condor-1 stations within 800 km and can store up to 64 kbits of data for subsequent relay to a Condor-3 site.

Earlier designs for an Okean-M spacecraft, with dual side-looking radars and other improved Earth observation sensors, have apparently been shelved in favor of a second generation system now known as the Sich-2 satellite (formerly known as Platform B) (Reference 741). Sich-2 will be launched by a Zenit-2 booster into a 650-km, sun-synchronous orbit. The overall dimensions of the horizontally oriented vehicle are 3.6 m in diameter and a length of 10.7 m, excluding the side-looking radar antenna. The spacecraft will have a 3-axis attitude control system with a pointing accuracy of 8 arc minutes.

The spacecraft bus will be a pressurized cylinder 1.9 m in diameter and 6.6 m long. A single solar array deployed above the spacecraft will deliver an average daily power of 800 W to the payload. The originally planned instrument suite will utilize both analog APT (137.4 MHz) and high capacity digital (8.2 GHz) data links. Sich-2 with a one-year capacity design life may also carry the Condor-2 data relay system.



REFERENCES

731. A. Yevtushenko, Poisk, 30 December 1993, p. 13.

732. Interfax News Agency, 20 September 1994.

733. ITAR-TASS News Agency, 24 January 1995.

734. UNIAN News Agency, 2 March 1995.

735. Y. Andreotti, Advances of Science and Technology, No. 21, 5 November 1985, pp. 1-5.

736. Information on Meteorological and other Environmental Satellites, op cit., p. V-17-V-22.

737. A. I. Kalmykov, et al, Determination of Oceanic Surface Structure with "Cosmos-1500" Satellite Side Looking Radar, Intercosmos Council, 1984.

738. M. V. Bukharov, et al, Issledovaniye Zemli Iz Kosmosa, May-June 1991, pp. 26-32.

739. A. I. Kalmykov, "Space-based Prediction of Catastrophes", NTR: Problemy I Resheniya, 1989, p. 3.

740. The "Yuzhnoye" Scientific-Production Association (NPO). Rocket-Space Research and Test Centre, Dnepropetrovsk, 1989.

741. Europe and Asia in Space 1991-1992, pp.138-139.



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