China launches BeiDou satellites
Two further BeiDou satellites were launched on 11 February.
A Long March-3B rocket launched the pair at around 05:00 UTC on 11 February from Xichang Satellite Launch Center, Sichuan province. It is reported that the satellites were successfully placed in their medium earth orbits (MEO) after just over 4 hours.
The satellites are believed to be Beidou-3MEO3 (Beidou-28) and Beidou-3MEO4 (Beidou-29) - third-generation spacecraft of the BeiDou (Compass) system featuring a phased array antenna for navigation signals and a laser retroreflector. The orbits are expected to be at ~21,500 km (~11,600 NM) inclined at 55.5º.
In a hectic period for BeiDou, immediate previous launches of pairs of MEO satellites have taken place on 5 November 2017 (-24 & -25) and 12 January 2018 (-26 & -27). BeiDou's Chief Designer is quoted as saying that China plans to launch a total of 18 BeiDou-3 satellites during 2018.
The Phase 3 BeiDou satellites are using a frequency centred at 1575.42 MHz and multiplexed binary offset carrier (MBOC) modulation - both features identical to the GPS L1 and Galileo E1 civil signals, making all 3 systems entirely compatible.
The current BeiDou Phase 2 covers the Chinese region with a claimed accuracy (95%) of 6 m horizontal and 10 m vertical. Phase 3 aims for full operational capability (FOC) by 2020 with a constellation of 35 satellites - 27 MEO plus 5 geostationary (GEO) and the existing 3 inclined geostationay (IGSO) satellites. This would give worldwide cover.
Further details from the link below . .