Long March 3C launches fifth Compass-G satellite into orbit

by Rui C. Barbosa

The Chinese were back in action on Friday, launching the fifth Compass-G satellite into orbit via their Long March 3C (Chang Zheng 3C) launch vehicle. The 16:12 UTC launch from the C2 launch complex of the Xichang Satellite Launch Center, in Sichuan Province was China’s third launch of the year.

Chinese Launch:

The Compass Navigation Satellite System (CNSS) is China’s second-generation satellite navigation system approved by the Chinese government in 2004, and is capable of providing continuous, real-time passive 3D geo-spatial positioning and speed measurement.

The system is used initially to provide high-accuracy positioning services for users in China and its neighboring regions, covering an area of about 120 degrees longitude in the Northern Hemisphere using five Compass-G, five Compass-IGSO and four Compass-M satellites.

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 around 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 see the coverage of the Chinese territory but in the future the Compass constellation will cover the entire globe.

Developed from the DFH-3B satellite platform, the Compass-G satellites orbit the planet on geostationary orbits and have a lifespan of 12 to 15 years. The satellites transmit signals on the: 1195.14-1219.14MHz, 1256.52-1280.52MHz, 1559.05-1563.15MHz and 1587.69-1591.79MHz, carrier frequencies.

The previous BeiDou-2 ‘Compass’ launch took place on December 1st, 2011, when a Chang Zheng-3A orbited the ‘Compass-I5’ (37948 2011-073A) satellite.

DFH-3B is an updated version of DFH-3 bus, a communications satellite bus whose capability is between high and medium ones. It adopts hexahedral structure, consisting of propulsion, service and communication modules, communication antennas and solar arrays and adopts 3-axis stabilized attitude control.

Its dimensions are 2200mm × 2000mm × 3100mm, and its mass is 3,800 kg with a payload mass of 400 kg to 450 kg. This satellite bus is applicable to communications and navigation satellites and deep space probes through adaptive modification.

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This was the eight flight of the CZ-3C Chang Zheng-3C launch vehicle that is primarily used for launching satellite to Geostationary Transfer Orbit (GTO). This rocket was developed to fill the gap between the CZ-3A Chang Zheng-3A and the CZ-3B Chang Zheng-3B, having a payload capacity of 3,800 kg for GTO. This is a three stage launch vehicle identical to the CZ-3B but only using two strap-on boosters on its first stage.

CZ-3C provides two types of fairing and two kinds of fairing encapsulating process and four different payload interfaces, which is the same as CZ-3B launch vehicle. The various fairing and interface adapter and the suitable launch capacity make CZ-3C a good choice for user to choose the launch service.

The development of the CZ-3C started in February 1999. The rocket has a liftoff mass of 345,000 kg, sporting structure functions to withstand the various internal and external loads on the launch vehicle during transportation, hoisting and flight.

The rocket structure also combines all sub-systems together and is composed of two strap on boosters, first stage, second stage, third stage and payload fairing.

The first two stages as well as the two strap on boosters use hypergolic (N2O4/UDMH) fuel while the third stage uses cryogenic (LOX/LH2) fuel. The total length of the CZ-3C 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-3C uses a DaFY6-2 engine with a 2961.6 kN thrust and a specific impulse of 2556.2 Ns/kg. The first stage diameter is 3.35 m and the stage length is 26.972 m.

Each strap on booster is equipped with a DaFY5-1 engine with a 704.4 kN thrust and a specific impulse of 2556.2 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 DaFY20-1 main engine (742 kN / 2922.57 Ns/kg) and four DaFY21-1 vernier engines (11.8 kN / 2910.5 Ns/kg each). The second stage diameter is 3.35 m and the stage length is 9.470 m.

The third stage is equipped with two YF-75 engines developing 78.5 kN each and with a specific impulse of 4312 Ns/kg. The fairing diameter of the CZ-3C is 4.00 meters and has a length of 9.56 meters.

The typical flight sequence of the CZ-3C for a standard GTO mission starts at T-0s with the ignition of the first stage engine and the two strap on boosters. Pitch over maneuver comes at T+10s. The strap on boosters end of ignition takes place at T+127.5s followed by boosters separation at T+129.0s.

First stage shutdown takes place at T+145.2 s, followed at T+146.7s by the first stage separation and ignition of the second stage. Separation of the fairing happens at T+258.7s. Second stage main engine shutdown takes place at T+328.0 s and second stage vernier shutdown occurs five seconds latter.

The separation of the second stage and the first ignition of the third stage take place at T+334.0s. This first ignition will last for 5 minutes and 16.6 seconds, ending at T+650.6s. After the first shutdown of the third stage the vehicle enters on a coast phase at T+654.1s, which will end at T+1323.2s with the second ignition of the third stage. This will end at T+1474.9s, beginning the velocity adjustment maneuver that lasts for 20 seconds.

Spacecraft separation occurs at T+1574.9s.

The first launch of the CZ-3C Chang Zheng-3C launch vehicle took place on April 25, 2008, when it orbited the first TL-1 Tianlian-1 tracking and data relay satellite.

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. 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.

Down range Tracking and Control stations of the launch center are located in Xichang City and Yibin City of Sichuan Province, and Guiyang City of Guizhou Province. Each of them houses tracking and measurement equipment for the powered phase of a launch vehicle flight.

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.

During 1993-1994 Xichang underwent extensive modernization and expansion, in part due to the requirements of the CZ-3 launcher family and in part to meet commercial customer needs.

The first launch from Xichang took place at 12:25UTC on January 29, 1984, when the CZ-3 Chang Zheng-3 (CZ3-1) launched the Shiyan Weixing (14670 1984-008A) communications satellite into orbit.

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