On 1 February, in the country’s second orbital launch mission in 2016, a CZ-3C rocket with a YZ-1 upper stage successfully placed a Beidou navigation satellite into orbit. The launch vehicle lifted off from Launch Complex 2 in the Xichang Satellite Launch Centre at 15:29 China Standard Time (07:29 UTC), carrying a single satellite named Beidou M3-S. The launch mission had a designation 07-70.
Beidou-III M3-S (with ‘M’ standing for the Medium Earth Orbit, or MEO, and ‘S’ standing for Shiyan, or ‘Experimental’) is the 21st satellite in the Beidou Satellite Navigation System. It is also the last of the five experimental satellites intended to demonstrate the technologies required for building a global satellite navigation network. The previous four experimental global navigation satellites (I1-S, M1-S, M2-S and I2-S) were launched in 2015 in three separate launch missions.
Mission Details
China began to construct a navigation satellite system in the late 1990s. Between 2000 and 2007, a total of four first-generation Beidou navigation satellites were placed into the Geostationary Earth Orbit (GEO) to form an experimental navigation constellation, capable of providing medium accuracy positioning services for China and East Asia.
Construction of a regional navigation satellite system (RNSS) named Beidou II or COMPASS began in 2007, with a total of 16 launch missions conducted between 2007 and 2012. Currently 14 of these satellites (including 5 in GEO, 5 in inclined geosynchronous orbit, and 4 in MEO) remain operational, providing navigation and positioning information within 10 m accuracy for China and its neighbouring countries. It can also measure speeds within 0.2 m per second, and provide signals for clock synchronisation accurate to 0.02 microseconds.
Construction of a global navigation satellite system (GNSS) unofficially known as Beidou III began in 2015. As the first step, five experimental satellites (two in inclined geosynchronous orbit and three in MEO) were to be launched to validate the satellite design and technologies, including inter-satellite communications link testing. By 2020, the network is to be expanded into a constellation consisting of 35 operational satellites to provide a global coverage.
The Satellite
Beidou-III M3-S was based on the navigation satellite bus developed by the Shanghai Engineering Centre for Microsatellites (SECM), a subsidiary of the China Academy of Sciences (CAS). It shares the same basic design as the Beidou III I1-S launched in April 2015. The satellite is 3-axis stabilised, with a total mass of under 1,000 kg.
The satellite’s mission payload was developed by the Southwest Institute of Electronic Equipment (SWIEE, or the 29th Institute), a subsidiary of the China Electronics Technology Corporation (CETC). Its features include transition of navigation services from regional to global, Ka-band inter-satellite links with the other four Beidou III satellites, a high degree of self-management for autonomous flight, and secondary mission for space environment exploration.
CZ-3C Launch Vehicle
The CZ-3C launcher rocket was designed and built by the China Academy of Launch Vehicle Technology (CALT), also known as CASC 1st Academy. The three-stage rocket is capable of placing up to 3,700 kg of payload into GTO. The CZ-3C was almost identical to the CZ-3B in design, but fitted with two strap-on boosters instead of four. A minor difference was that the 3C model didn’t have the stabilising fins found at the bottom of the boosters on the CZ-3B.
Development of the CZ-3C began in March 1995, and the rocket was almost ready by March 1996. However, following the CZ-3B incident on 15 February 1996, the CZ-3C development was suspended so that CALT could focus on improving the CZ-3B. The two satellites originally scheduled to be launched by the CZ-3C were launched on the CZ-3B instead. The 3C variant didn’t make its maiden flight until 12 years later in 2008.
The two strap-on liquid boosters, first-stage, and second-stage of the rocket all burn the N2O4/UDMH bi-propellant, while the third-stage burns the LOX/LH2 bi-propellant. The basic variant of the launch vehicle is 55 m tall and weighs 345 t at lift-off.
Yuan Zheng-1 Upper Stage
This was also the third flight mission of the Yuan Zheng-1 (YZ-1 or “Expedition-1”) upper stage, which has been added to the three-stage CZ-3C to provide the capability to directly insert the satellite into high orbits without the need to use the satellite’s own propulsion. This stretched the total length of the launch vehicle to 57.126 m. After separation from the third-stage of the launcher, the liquid-fuelled YZ-1 upper stage began its first burn to raise the apogee of the orbit to a higher orbit, eventually reaching a near circular orbit (apogee: 21,982 km; perigee: 21,513 km; inclination 55.0°).
