China orbited its fourth tracking and data relay satellite in the Tianlian-1 range known as ‘Sky Link’ on Tuesday. The launch took place at 15:24 UTC from the Xichang Satellite Launch Center in Sichuan Province, utilizing a Long March 3C/G2 launch vehicle.



Chinese Launch:

The Chinese tracking and data relay satellites were developed by the China Academy of Space Technology (CAST) and it is similar to the American Tracking and Data Relay Satellite System (TDRSS) in its concept.

The system is designed to support near-real-time communications between orbiting spacecraft and ground control. The system will complement the ground-based space tracking and telemetry stations and ships to support future space projects.

Like its predecessors, the Tianlian-1 (4) satellite is based on the DFH-3 bus. The DFH-3 (Dongfanghong-3) platform is a medium-capacity telecommunications satellite platform designed and developed by CAST.

The spacecraft can carry multiple telecommunications payloads for providing numerous services, such as fixed communication, international satellite communication, national and regional communication, wideband data communication, mobile communication and direct broadcast; military communication, spacecraft tracking and data relay.

The platform comprises six subsystems: control, power, propulsion, measurement & control, structure and thermal control subsystem. The platform configuration features module subdivision, which includes communication module, propulsion module, service module and solar array. The platform also adopts three-axis stabilized attitude control mode, having solar array output power of 1.7 kw by the end of its design lifetime of 8 years. It has a mass of 2,100kg with payload capacity 220kg.

The DFH-3 satellite platform has been successfully applied in DFH-3 satellite, Beidou navigation test satellite, and other satellites, all of which are currently operating normally.

During numerous flight missions, the maturity and reliability of the DFH-3 platform is China’s proven system. Moreover, it has strong expansion capacity and can be upgraded to some space exploration missions, such as meteorological satellite, lunar resource satellite services.

Currently, Tianlian-1 (1) is positioned at 77°E. This satellite was launched on April 25, 2008 by the first Long March-3C launch vehicle.

Tianlian-1 (2) is positioned at 176.77°E, following its July 11, 2011 launch on a Long March-3C (Y8) launch vehicle. With the launch of Tianlian-1 (3) on July 25, 2012, China has managed full global coverage for its tracking and data relay system.

Launch vehicle and launch site:

The Long March-3C launch vehicle was developed to fill the gap between the Long March-3A and the Long March-3B, having a payload capacity of 3,800 kg for GTO or 9,100 kg to LEO. This is a three stage launch vehicle identical to the LM-3B but only using two strap-on boosters on its first stage.

The LM-3C/G2 is based on the LM-3C but has a lengthened first stage and boosters, which increases the GTO launch capability.

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

The development of the LM-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, a first stage, a second stage, a 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 LM-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 LM-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 LM-3C is 4.00 meters and has a length of 9.56 meters.

Inaugurated on January 29, 1984, when the first Long March-3 was launched to orbit the Shiyan Weixing (14670 1984-008A) communications 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

Downrange 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.