More details about Soyuz anomaly during launch of Glonass-M

Recent problems which appeared during last launch performed from Plesetsk cosmodrome were related with last stage of Soyuz-2.1B.

Anomaly appeared during mission of Soyuz-2.1B/Glonass-M which started on May 29, 2016 at 08:45 GMT from Plesetsk cosmodrome. Mission was planned as part of modernization program of Russian GLONASS (Globalnaya Navigationnaya Sputnikovaya Sistema-Global Orbiting Navigation Satellite System) navigation system by adding new generation M satellites to replace first generation of Glonass satellites which are base of system since 1982. Lifted satellite started its lasting 7 years mission after correct separation from Fregat-M upper stage performed on May 29, 2016 at 12:16 GMT.

Just after launch TASS news agency stated that Fregat-M upper stage performed longer burn then it was originally planned. It was confirmed that problems appeared in third stage of Soyuz; RD-0124 engine worked for a shorter period of time, but Fregat upper stage, thanks to its propulsion and load of 5600 kg N204/UDMH propellant, was able to operate its propulsion for prolonged time and deliver Glonass-M to designated parking orbit. On June 2, 2016 it was unveiled that according some sources engine in third stage stopped its RD-0124 engine 5 seconds before planned moment (burn time for third stage of Soyuz is 270 seconds). It caused malfunction alert in Fregat-M upper stage and in consequence necessity of recalculating flight parameters by Fregat-M onboard computer. Fregat-M extended its burn time of S5.92 engine to 150% to compensate insufficient speed achieved by third stage of Soyuz. It was possible mainly due the advanced construction of Fregat-M. It is equipped with independent guidance, navigation, attitude control, tracking and telemetry systems which are monitoring flight parameters in real time. After spotting that any parameter is not correct, flight computer recalculates parameters (like thrust in this case) to help in reaching correct orbit.

Sources:
http://novosti-kosmonavtiki.ru/

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