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Shijian-13 ( Shíjiàn shísānhào) is the first high-throughput communications satellite in China. It was launched from Xichang Satellite Launch Center and developed by the China Academy of Space Technology(CAST) which belongs to China Aerospace Science and Technology Corporation(CASC). The satellite first time uses a Ka-band broadband communications system and the ability of data transmission will greatly enhanced. Its total transfer capacity is more than 20 GB, this improved about tenfold compare to the previous. The total message capacity of Shijian-13 satellite exceeds the total capacity of all communication satellites developed previously. China is developing high-throughput communications satellite to form a high-bandwidth mobile communication system which can cover most areas and offshore sea areas. The high-speed internet access becomes a reality in the airplane cabins, on high-speed rails, also in remote mountain areas. January 23, 2018, China’s first high-throughput communications satellite was put into use officially.

Background information
Electric propulsion and thruster system is an advanced propulsion technology. It is a device which generates thrust without depending on chemical combustion. The electric propulsion eliminates the requirements for solid or liquid fuels and it can reduce the fuel carrying capacity of spacecraft significantly. Originally, a satellite required for 3 tons of chemical propellant, if adopt electric propulsion only 300 kg of propellant is required which can reduce the satellite weight and increase the payload theoretically. The three main features of electric propulsion are high specific impulse, long lifetime and low thrust which can lead to a high controlling precision, and its specific impulse can achieve more than 3,000 seconds, which is 10 times more than the conventional chemical propellants. The effect of the high specific impulse is to reduce the amount of propellant significantly which is carried by the satellite and provide more spaces for the payload. The Dongfanghong-3 B platform is the latest generation of medium-capacity communication satellite platform which is developed by China. It uses the technologies of integrated avionics system, electric propulsion, high-efficiency thermal control, lithium-ion battery, FDIR and other advanced technologies. This platform technology can be popularized to other satellite platforms.

Launch
The first high-throughput communications satellite Shijian-13 was launched on April 12, 2017 at 7:04 pm successfully by the Long March 3B (LM-3B/CZ-3B) which is a carrier rocket, from the Xichang Satellite Launch Center in southwest China's Sichuan Province. This flight mission is the 246th launch of the Long March Launch Vehicle. Shijian-13 communication satellite discovered and acquired the target near the equator successfully with Yuan Wang 6 which is thousands of miles away from Xichang, for protecting the rocket flight and made an important contribution to the successful launch of Shijian-13. On January 23, 2018, China’s first high-throughput communications satellite Shijian-13 was delivered in-orbit and put into use officially. During the in-orbit test, 11 experimental projects were completed and finished by the Shijian-13. The success of the test on the broadband multimedia satellite communications system of Shijian-13 and its high speed laser communication technology between the first high-speed satellite and the ground. It lays a foundation for the important project of China on the “space-ground integrated information network” project. The design concepts of the “space-ground integrated information network” project can make Shijian-13 communications satellite provide high-speed “Satcom on the Move” (SOTM) which is a new concept for the traditional Multimedia Messaging Service (MMS), it refers to the protection of the satellite communication of the moving carriers such as vehicles, ships and airplanes during the movement. It improves the online experience for passengers on shipping, aviation, railway and other vehicles thoroughly. The higher frequency Ka-band broadband communications makes the satellite can transmit high-definition (HD) videos and the receiving terminal is small which is easy to carry. In addition, Shijian-13 communications satellite can play a pivotal role of  emergency communications through without building a network separately, cost-effective and other features.

Function of Satellite
In China, Shijian-13 is the first high-throughput communications satellite which is a high-orbit test satellite that can test and verify the B platform and payload technology of Dongfanghong 3. In the past, it was able to transfer dozens of standard definition (SD) television programs and channels at the same time. However, with the increase of satellite flux, dozens of even 4K ultra high definition (UHD) quality television programs and channels can be transmitted at the same time for helping people to access the internet on airplanes and high-speed trains without barriers. Shijian-13 can provide higher quality on WIFI service and transfer more high definition (HD) television channels at the same time. In China, it is estimated within three years, there are more than 2,000 airplanes, more than 3,000 high-speed trains and tens of thousands of ships can be achieve high speed and quality internet access anytime and anywhere. Shijian-13 satellite can also provide better internet connection for airplanes and high-speed trains by increasing the satellite throughput. Shijian-13 can provide the better internet access in less-developed regions, also on high-speed rails and airplanes by large message capacity. Shijian-13 satellite can help report on emergencies of natural disasters and allows passengers to watch high-definition videos on high-speed rails. The technologies on Shijian-13 can decrease the chemical fuel that is carried by satellite extensively.

Significance of Research
Through the completion of the test verification on Shijian-13 communication satellite, it will be transferred to the Ka-band broadband communications test service and will be included into the China Sat series for making China to control an advanced technology which is the Ka-band broadband communications system follows the United States, Europe and a little mount of developed countries. Shijian-13 communication satellite is not limited by the ground conditions and it can provide better broadband signal services for users who lives in the underdeveloped areas and promote the wide range adoptions of broadband satellite communications in high-speed trains, ships, airplanes and other mobile carriers. The most important significance of Shijian-13 is that it has the bandwidth capacity to meet the needs of the civil industries. Whether it is a remote mountain village, desert, island, peak, or the aircrafts, trains and ships which can not covered by the 2G/3G/4G signal, and the place where the ground wireless signal is not covered or the cable can not reach the access. Under the above situations, it can be all connected to the network by the Shijian-13 satellite easily.

Technological innovation
It was necessary to utilise pre-existing technological systems and components for the first time during the development of Shijian-13. Shijian-13 communications satellite has a variety of the technologies used that China never used on any communications satellites before.

Electric propulsion technology
Shijian-13 is a first Chinese communications satellite which uses electric propulsion technology on the satellite. Electric propulsion is an advanced space propulsion technology. Compared to the common chemical propulsion, the electric propulsion system has the features of the high specific impulse, low thrust and long lifetime. The application of an electric propulsion system on a long-life spacecraft can reduce the carrying capacity of the propellant sharply, therefore the satellite can reduce its own weight, save the spaces and carry more payload.

Laser communications system
This is the first laser communications system that China used on the communications satellite which is Shijian-13 satellite. Shijian-13 uses the laser communications system with the high orbit satellite. The laser communication system has the advantages of high bandwidth and high transmission rate, it can meet the requirements of high-capacity and high-rate communication. Shijian-13 also has a successful test on the high speed laser communication technology between the high-orbit satellite and the ground and the rate of speed is up to 2.4Gbps.

Domestic components
For Shijian-13, its the first time that China uses a huge number of domestically produced products on the communications satellite with a long high-orbital life, which changed the long-term dependence on imports of the related products.

Ka-band broadband communications system
The Ka-band broadband communications system installed on the Shijian-13 satellite is the first usage on the China’s communications satellites. The total message capacity of Shijian-13 satellite exceed the total capacity of all communications satellites which were developed previously. The ability of data transmission will greatly enhanced, the total transfer capacity is more than 20 GB. It can support multi-user and large-capacity payload. It can also download the data with a high-speed in the most areas through the satellite and support a large number of users to upload data with the higher speed. Shijian-13 communications satellite can cover the most areas of the land and the hundred kilometers of offshore area in China, except the northwest and the northeast of China.

Technical test and demonstration application
Shijian-13 is the first Chinese communications satellite that has the combination of technical test and demonstration application on satellite. It will accelerate the application and transformation of the scientific research results. This combination is not only meets the purpose of the new technologies for in-orbit test, but also meets the requirements of payload demonstration applications and improves the comprehensive benefits of the project.

Relevant institutions
The China Aerospace Science and Technology Corporation (CASC) and the China Academy of Launch Vehicle Technology (CALT) are the two relevant institutions which designed the rocket and satellite. The project of Shijian-13 communications satellite includes six major systems, the China Aerospace Science and Technology Corporation (CASC) which is in Beijing has undertaken the related tasks of the operational control and test application systems. The Long March 3B carrier rocket which has responsibility for the launch mission of Shijian-13, was developed by the China Academy of Launch Vehicle Technology (CALT) which is the subordinate of the China Aerospace Science and Technology Corporation (CASC). This launch was the 246th launch of the Long March series of launch vehicles. The Shijian-13 satellite and launch vehicle are respectively developed by China Academy of Space Technology (CAST) and China Academy of Launch Vehicle Technology (CALT). The ion thruster for Shijian-13 is developed by the Lanzhou Institute of Physics, this institution is the relevant institution. The project of Shijian-13 communications satellite was organized and implemented by the State Administration for Science, Technology and Industry for National Defense (SASTIND). The ground monitoring and control system is belongs to the Xi'an Satellite Control Center.