GLONASS Update Delves into Constellation Details
At the Civil GPS Service Interface Committee meeting in Portland, Oregon, on Monday, Sergey Revnivykh, Deputy Director General of Roscosmos’s Central Research Institute of Machine Building reported on the status and future of GLONASS.
He provided a number of previously unpublished details on the present constellation and how it will be augmented in the future.
The present constellation officially has two reserve satellites, GLONASS 714 and 726. Revnivykh stated that neither of these satellites would ever be brought back to active service. 714 was a flight-test satellite, apparently, and 726 had a failure of its navigation payload. Rather than being possible replacement satellites, these vehicles are being used to train the ground team to operate spare satellites in a full or nearly full constellation.
GLONASS 727, in orbital slot 3, which was taken out of service on 8 September 2010 has also had a failure of its navigation payload and will not be returning to service. About 11 more GLONASS-M satellites will be launched by the end of 2012.
Revnivykh announced that there will be two versions of the new GLONASS-K satellites: GLONASS-K1 and GLONASS-K2. GLONASS-K1 satellites will have a 10-year design life and a daily clock stability of 5 ´ 10-14. The first GLONASS-K1 satellite will be launched this December from the Plesetsk Cosmodrome about 800 km north of Moscow. This will be the first launch of a GLONASS satellite from other than the Baikonur Cosmodrome. Only one more GLONASS-K1 satellite will be built and launched after that. The K1 satellites will test an open service CDMA signal on the GLONASS L3 frequency in the 1205 MHz band. When asked when the specific structure of the CDMA signal would be announced, Revnivykh said he didn’t know.
A completely new design, GLONASS-K2, will start launching in 2013. GLONASS-K2 satellites will have a 10-year design life and a clock stability of 1 ´ 10-14. Besides the CDMA signals on L3, CDMA signals will also be transmitted on L1 and L2. The GLONASS-K satellites will transmit the legacy FDMA satellites in addition to the CDMA signals.
A modernized GLONASS-K satellite, GLONASS-KM, for launch after 2015 is now under study. In addition to transmitting legacy FDMA signals on L1 and L2 and CDMA signals on L1, L2, and L3, CDMA signals may also be transmitted on the GPS L5 frequency at 1176.45 MHz. Also being studied is an alternative to the present three-plane, equally spaced satellite constellation. A different constellation design would be possible using CDMA signals. Such a move would require that the legacy FDMA signals be switched off. Revnivykh stated that any such move would require at least 10-years’ advance notice.
The design characteristics of the various generations of GLONASS satellites are shown in Figure 1, taken from Revnivykh’s presentation.
Figure 1. The GLONASS satellite generations through GLONASS-K2.
The signals that will be transmitted by the future generations of GLONASS satellites as well as those transmitted by the initial GLONASS satellites and the GLONASS-M satellites now on orbit are shown in Figure 2.
Figure 2. Signals transmitted by the different generations of GLONASS satellites. OF = open-access FDMA, SF = special (military) FDMA, OC = open-access CDMA, OCM = open-access CDMA modernized.
Revnivykh also spoke on the satellite-based augmentation system, SDCM (System for Differential Correction and Monitoring), under development. Correction and integrity data will be transmitted by Luch geostationary communication satellites now under development. Luch 5A, to be launched in 2011 and positioned at 16°W longitude and Luch 5B, to be launched in 2012 and positioned at 95°E longitude, will transmit signals on an L1 frequency. Luch 4, to be launched in 2013 and positioned at 167°E longitude, will transmit on two frequencies. The three satellites will provide almost global coverage. The satellite payloads are under development.
According to Revnivykh, the SDCM will make use of 12 monitor stations currently in operation in Russia and one in Antarctica at Russia’s Bellingshausen research station. However, the SDCM website indicates only 10 Russian stations currently in the test network. Eight more monitor stations will be added in Russia and five more outside Russia. Revnivykh showed a map revealing the locations of the additional overseas stations as Cuba, Brazil, Vietnam, Australia, and an additional station in Antarctica. It is not intended, at least initially, that these stations would be used in generating the orbit and clock data broadcast by the GLONASS satellites themselves.
And finally, Revnivykh stated that a GLONASS performance document will be released in the 2012-2013 time frame.
Revnivykh’s full presentation will be available on the U.S. Coast Guard Navigation Center website by the end of next week.
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