The fifth Chinese launch in September took place at 23:13 UTC on Tuesday (Wednesday morning local time) with a Long March-3B/G2 rocket orbiting another Beidou-3 navigation satellite. The launch of BDS I2-S (or Beidou-20) took place from the Xichang Satellite Launch Center via the modified pad 3.
Tuesday’s launch is another steady step in the completion of the Phase III of the Beidou program several years ahead of schedule – by as soon as 2017, rather than 2020.
However, the launch initially received a blackout in the Chinese media, with lift-off only confirmed by local observers. It took over an hour – once the spacecraft was successfully deployed – for the Chinese media to acknowledge the launch.
The Beidou Phase III system includes the migration of its civil Beidou 1 or B1 signal from 1561.098 MHz to a frequency centered at 1575.42 MHz – the same as the GPS L1 and Galileo E1 civil signals – and its transformation from a quadrature phase shift keying (QPSK) modulation to a multiplexed binary offset carrier (MBOC) modulation similar to the future GPS L1C and Galileo’s E1.
The current (Phase II) B1 open service signal uses QPSK modulation with 4.092 megahertz bandwidth centered at 1561.098 MHz.
The current Beidou constellation of geostationary (GEO) – five inclined geosynchronous orbit (IGSO), and four middle Earth orbiting (MEO) – spacecraft are transmitting open and authorized signals at B2 (1207.14 MHz) and an authorized service at B3 (1268.52 MHz).
Real-time, stand-alone Beidou horizontal positioning accuracy was classed as better than 6 meters (95 percent) and with a vertical accuracy better than 10 meters (95 percent).
The Compass Navigation Satellite System (CNSS) is China’s satellite navigation system, approved by the Chinese government in 2004, capable of providing continuous, real-time passive 3D geo-spatial positioning and speed measurement.
The Chinese navigation system is being developed and deployed in three phases: Phase 1 (starting in 2003), consisted of an experimental regional navigation system, BeiDou-1, which provided active navigation service; Phase 2 (started in 2012), consisted of a reduced satellite constellation and provides open service over China.
This phase aimed at deploying a system with passive positioning and timing capability over a regional area; Phase 3 (starting in 2020), by 2020, the system would reach full operational capability with a constellation of 27 MEOs plus 5 GEOs and the existing 3 IGSOs satellites of the regional system. CNSS would provide global navigation services, similarly to the GPS, GLONASS or Galileo systems.
CNSS is expected to support two different kind of general services: RDSS and RNSS. In the Radio Determination Satellite Service (RDSS), the user position is computed by a ground station using the round trip time of signals exchanged via GEO satellite.
The RDSS Long term feature further includes: short message communication (guaranteeing backward compatibility with Beidou-1), large volume message communication, information connection, and extended coverage.
The Radio Navigation Satellite Service (RNSS) is very similar to that provided by GPS and Galileo and is designed to achieve similar performances.
The long-term goal is to develop a global navigation satellite network similar to the GPS and GLONASS by 2020 eventually consisting a constellation of 35 vehicles, including 27 MEO (21,500 km orbits) satellites, three IGSO satellites (inclined at 55 degrees) and five GSO satellites.
The system will be dual use, based on a civilian service that will provide an accuracy of 10 meters in the user position, 0.2 m/s on the user velocity and 50 nanoseconds in time accuracy; and the military and authorized user’s service, providing higher accuracies.
The first phase of the project will involve coverage of the Chinese territory. However, the future Compass constellation will cover the entire globe.
The new satellite – now named as BDS I2-S (Beidou-20) – uses a new bus that feature a phased array antenna for navigation signals and a laser retroreflector. Launch mass is about 800/850 kg and the satellites have an operational lifespan of 10 years. Previous BDS I1-S satellite was built by the Shanghai Small Satellite Center of the Chinese Academy of Sciences (CAS).
Launcher and launch center:
Developed from the Chang Zheng-3A, the Chang Zheng-3B is the most powerful launch vehicle on the Chinese space launch fleet.
The CZ-3B features enlarged launch propellant tanks, improved computer systems, a larger 4.2 meter diameter payload fairing and the addition of four strap-on boosters in the core stage that provide additional help during the first phase of the launch.
The rocket is capable of launching a 11,200 kg satellite to a low Earth orbit or a 5,100 kg cargo to a geosynchronous transfer orbit.
The CZ-3B/G2 (Enhanced Version) launch vehicle was developed from the CZ-3B, increasing the GTO capacity up to 5,500kg.
On May 14, 2007, the first flight of CZ-3B/G2 was performed successfully, accurately sending the NigcomSat-1 into pre-determined orbit. With the GTO launch capability of 5,500kg, CZ-3B/G2 is dedicated for launching heavy GEO communications satellite.
The rocket structure also combines all sub-systems together and is composed of four strap-on boosters, a first stage, a second stage, a third stage and payload fairing.
The first two stages as well as the four strap-on boosters use hypergolic (N2O4/UDMH) fuel while the third stage uses cryogenic (LOX/LH2) fuel. The total length of the CZ-3B is 54.838 meters, with a diameter of 3.35 meters on the core stage and 3.00 meters on the third stage.
On the first stage, the CZ-3B uses a YF-21C engine with a 2,961.6 kN thrust and a specific impulse of 2,556.5 Ns/kg. The first stage diameter is 3.35 m and the stage length is 23.272 m.
Each strap-on booster is equipped with a YF-25 engine with a 740.4 kN thrust and a specific impulse of 2,556.2 Ns/kg. The strap-on booster diameter is 2.25 m and the strap-on booster length is 15.326 m.
The second stage is equipped with a YF-24E (main engine – 742 kN / 2,922.57 Ns/kg; four vernier engines – 47.1 kN / 2,910.5 Ns/kg each). The second stage diameter is 3.35 m and the stage length is 12.920 m.
The third stage is equipped with a YF-75 engine developing 167.17 kN and with a specific impulse of 4,295 Ns/kg. The fairing diameter of the CZ-3B is 4.00 meters and has a length of 9.56 meters.
The CZ-3B can also use the new Yuanzheng-1 (“Expedition-1″) upper stage that uses a small thrust 6.5 kN engine burning UDMH/N2O4 with specific impulse at 3,092 m/s. The upper stage is able to conduct two burns, having a 6.5 hour lifetime and is capable of achieving a variety of orbits. This upper stage was not used on this launch.
The Xichang Satellite Launch Centre is situated in the Sichuan Province, south-western China and is the country’s launch site for geosynchronous orbital launches.
Equipped with two launch pads (LC2 and LC3), the centre has a dedicated railway and highway lead directly to the launch site.
Tuesday’s launch took place from the modernized Pad LC3.
The Command and Control Centre is located seven kilometers south-west of the launch pad, providing flight and safety control during launch rehearsal and launch.
The CZ-3B launch pad is located at 28.25 deg. N – 102.02 deg. E and at an elevation of 1,825 meters.
Other facilities on the Xichang Satellite Launch Centre are the Launch Control Centre, propellant fuelling systems, communications systems for launch command, telephone and data communications for users, and support equipment for meteorological monitoring and forecasting.
The first launch from Xichang took place at 12:25UTC on January 29, 1984, when the Chang Zheng-3 (Y-1) was launched the Shiyan Weixing (14670 1984-008A) communications satellite into orbit.