GNSS Constellation Updates
December 20, 2011The following updates to GNSS constellations is provided by the CANSPACE Listserv.
GPS
SNV27/PRN27 has been set healthy.
SVN27/PRN27, a Block IIA satellite launched in 1992, had been decommissioned on 10 August 2011. The satellite had been removed from broadcast almanacs but continued to transmit L-band signals, presumably for continued testing, and was continuously tracked by some stations of the International GNSS Service tracking network.
Apparently declared still operationally useful, SVN27/PRN27 was transitioned into the broadcast almanac on 15 December 2011 after 22:00 UTC (ref. NANU 2011101) and was set usable on 16 December 2011 at 22:42 UTC (ref. NANU 2011105). This move brings the GPS constellation back to 31 fully operational satellites.
GLONASS
GLONASS 745 has replaced GLONASS 712 in orbit slot 7 / frequency channel 5.
GLONASS 712 was set unhealthy shortly before 21:00 UTC on 14 December 2011 and stopped transmitting L-band signals on its assigned frequency channel 5 shortly thereafter. It is now considered an official back-up or spare satellite. GLONASS 745 started transmitting on frequency channel 5 from orbit slot 7 at about 06:00 UTC on 15 December and was added to the broadcast almanac but initially set unhealthy. It was subsequently set healthy and put into operation on 18 December 2011 at 08:00 UTC (ref. NAGU 061-111219).
GLONASS 744, launched with GLONASS 743 and 745 from the Baikonur Cosmodrome on 4 November 2011, had been set healthy on 8 December 2011 at 07:42 UTC (ref. NAGU 057-111208).
Based on NORAD/JSpOC tracking, GLONASS 743 is still in transit to orbit slot 2.
GLONASS 746, launched from the Plesetsk Cosmodrome on 28 November 2011, arrived at its designated orbit slot 17 in plane 3 on or about 13 December. It is not yet active.
The GLONASS System Control Centre has announced that GLONASS 746 is replacing GLONASS 714 in orbit slot 17. According to the Roscosmos Analytical-Information Centre, transmissions from GLONASS 714 on frequency channel 4 were stopped at about 21:01 UTC on 19 December. Transmissions from GLONASS 746 started up at around 06:00 UTC on 20 December and the satellite is being tracked by several stations in the IGS tracking network. GLONASS 746 is not yet set healthy but is
expected to be so within the next few days. GLONASS 714 has been declared a reserve or spare satellite.
Beidou-2/Compass
The fifth Beidou-2/Compass inclined geosynchronous orbit (IGSO) satellite, launched on 1 December 2011, has achieved its IGSO orbit. NORAD/JSpOC published orbital element sets indicate this was achieved sometime between 9 December and 13 December. There were no published element sets between these dates. NORAD/JSpOC typically loses track of satellites temporarily when they execute delta-V manoevres.
IGSO 5 has joined IGSO 4 with a nominal orbit centred on an east longitude of 95 degrees. The other three Beidou-2/Compass IGSO satellites are clustered in a group at a nominal east longitude of 118 degrees. The satellites are allowed to drift slightly from their nominal orbit slots as this figure shows.
Also shown in the figure are the locations of the three operational Beidou-2/Compass geostationary Earth orbit (GEO) satellites.
SDMA
Luch-5A, the first of a set of new geostationary satellites to reactivate Roscosmos's Luch Multifunctional Space Relay System
launched on 11 December 2011, carries a System for Differential Correction and Monitoring (SDCM) transponder. SDCM is a satellite-based augmentation system (SBAS) for GLONASS and GPS, compatible with the U.S. Wide Area Augmentation System and other SBASs. Published reports have stated that the satellite is to be positioned at 16 degrees west longitude. According to NORAD/JSpOC tracking, the satellite made an initial transition from its parking orbit to a GEO orbit on 12 or 13 December. There have been no published element sets since 13 December, which likely indicates that another delta-V occurred and NORAD/JSpOC has temporarily lost the satellite.
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