GLONASS Modernization: Maybe Six Planes, Probably More Satellites

January 10, 2012  - By
Image: GPS World

According to the GLONASS Information-Analytical Centre, proposals made at a December 27, 2011 meeting on the status and future of the satellite constellation included one to expand the GLONASS constellation to 30 satellites using six orbital planes. Five other options for upgrading the constellation were also aired, a draft of the tactical and technical requirements for GLONASS in 2025 was reviewed, and a report was given on the status the Glonass-K2 satellite under construction and the timing of the start of flight tests.

Present at the meeting of the Presidium of the TsNIImash Council, held in the Moscow suburb of Korolyov, were Yuri Urlichich, general director and general designer of the Joint Stock Company (JSC) Russian Space Systems, and Sergey Revnivykh, TsNIImash deputy director general, among others. TsNIImash (the Central Research Institute of Machine Building) is the arm of Roscosmos, the Russian Federal Space Agency, with responsibility for civil aspects of GLONASS.

A press conference following the meeting discussed the six options for upgrading the constellation, foremost among them the six-plane, 30-satellite concept. The other options include adding one more satellite to each of the existing three planes, but that would involve rephasing almost all of the operating satellites, which could cause many problems, according to Urlichich. Another option would add a reserve satellite to each operating satellite, but that option had already been rejected. Adding three new planes to the constellation, each with two satellites, is the leading option; Urlichich said this would be considered in detail over the next few months.

It is not clear how the present frequency division multiple access (FDMA) channel spectrum used by GLONASS could handle 30 satellites. As indicated in the current publicly available version of the GLONASS Interface Control Document (version 5.1, dated 2008), there are 14 available channels (channel numbers from -7 to +6), with antipodal satellites sharing the same channel. It appears that this arrangement can only handle a maximum of 28 satellites. However, at least one recent GLONASS spectrum plot shows GLONASS channels going from -7 to +8, rather than to +6 as in the ICD. Such an expansion to 16 channels could support 32 satellites and is a partial return to the pre-2005 use of higher frequency channels, although the Russians had previously agreed to abandon their earlier use of the higher channels to avoid interfering with radio astronomers’ use of the 1610.6-1613.8 MHz observation band to observe the spectral line of the hydroxyl molecule.

Nevertheless, the six-plane concept is still only just that — a concept — and the Russian Defense Ministry among others would have to get on board for it to go ahead.

SBAS. Information on the Russian satellite-based augmentation system, the System for Differential Correction and Monitoring or SDCM, was also revealed during the press conference. SDCM will use a global ground network of monitoring stations and transponders on the Luch Multifunctional Space Relay System geostationary communication satellites to transmit correction and integrity data using the GPS L1 frequency. The first of these satellites, Luch-5A, was launched on 11 December.

Luch-5A is temporally located in a stable geostationary orbit at about 58.5 degrees east longitude according to U.S. tracking data. Testing of the satellite is being carried out at this location but it will eventually be deployed to 16 degrees west longitude for operational use. It was announced during the press conference that SDCM testing is to start after the Russian Christmas holidays.

Negotiations for additional SDCM ground stations in Australia, Indonesia, Brazil, and Nicaragua are ongoing to provide adequate coverage in the southern hemisphere. If one or more of the proposed ground stations cannot be realized, then additional stations at Russia’s Antarctic research bases could be deployed, Urlichich said. SDCM already has stations at the Bellingshausen and Novolazarevskaya research bases. Presentations by TsNIImash staff at international meetings have indicated that additional stations could be installed at the Progress and Russkaya Antarctic bases. According to Urlichich, the SDCM stations on Russian territory could be sufficient for northern hemisphere coverage.

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