A Russian Soyuz-2-1b rocket will launch from the Plesetsk Cosmodrome Saturday night, deploying a replacement satellite for the GLONASS navigation system with the aid of a Fregat-M upper stage. Liftoff is due to take place at 23:17 Moscow Time (20:17 UTC), beginning a three-and-a-half hour journey to the spacecraft’s destination orbit.
Russia’s GLONASS navigation system is served by a constellation of satellites named Uragan, meaning Hurricane. The current-generation Uragan-M spacecraft are designed for seven years of service, with new satellites being launched as needed to replace failing spacecraft on orbit. Saturday’s launch will deploy Uragan-M No.757 – the forty-eighth Uragan-M and the 137th GLONASS satellite overall.
Like the US Global Positioning System and Europe’s Galileo, GLONASS uses satellites in medium Earth orbit broadcasting highly-accurate timing signals which receivers can use to triangulate their locations. GLONASS satellites broadcast four navigation signals in the L-band: unrestricted L1 and L2 signals for civilian use, and equivalent restricted signals for the Russian military.
Accurate timing is maintained for these signals by caesium atomic clocks aboard the satellites. GLONASS requires twenty-four satellites, stationed in three planes of eight spacecraft each, to provide worldwide service. Saturday’s launch appears to be targeting the second plane of the ...