Chinese Satellite Communications Systems
By 1994 China had opened 8100 post and telecommunications satellite communications lines, 11 television satellite lines and 30 broadcasting lines. These communications satellites perform the transmission of TV, broadcasting and education TV programs of the central committee, provinces and cities, and carry out the public communications between China and other countries, and special communications for such state agencies as finance, water and electricity, energy, transportation and public security, etc.. The successfully launched communications broadcasting satellites have opened many application items, such as digital and simulation telephone, TV and broadcast items transmission, facsimile, data report form transmission and TV education communications.
To satisfy increasing communications needs, consolidate domestic markets, and penetrate international markets, by the mid 1990s China was focused on the development of satellites of higher quality and lower cost. The Chinese Academy of Space Technology, having developed and launched two generations of communications satellites, began reviewing its satellite experience and was studying foreign technology and management methods.
The first step was to standardize a common platform bus for a series of satellites. The platform is the base of a satellite. The use of a standard common platform can simplify the work of developing a new platform for each new satellite. A few standard platforms capable of satisfying the needs of various payloads will be developed. The main objectives of this approach are to reduce development time, to improve satellite quality, and to lower costs. The Chinese space industry developed four series of standard platforms, one of which was a geostationary orbit satellite platform to be used in communications satellites.
The DJS-1 platform used by the DFH-3 communications satellite can support a payload weight of 150 to 170 kilograms, while its solar array is capable of generating 1,600 to 2,200 watts of electrical power to supply a payload electric power requirement of 900 to 1,000 watts. The DJS-1 platform also had 1,270 kilograms of available propellant for orbital maneuvers and an expected lifetime of eight to ten years. The DJS-1 platform will be used to build additional medium-capacity communications satellites and to provide dual-band (Ku- and C-band) communications, mobile communications, data transmission, and other services.
To satisfy the demand for large-capacity satellites, China planned to develop a third generation of communications satellite, one with large capacity and a large platform bus, dubbed DJS-2. The main capabilities of one option tentatively planned for the DJS-2 included such features as the ability to support a payload weight of between 400 and 500 kilograms, a solar array output of 4,500 to 6,000 watts, electric power available for payloads of 3,000 to 4,700 watts, 2,200 kilograms of propellant available for orbital maneuvering, and an operational lifetime of fifteen years. The DJS-2 common platform would be able to carry twelve Ku-band transponders of 100-watt output and twenty-four C-band transponders of sixteen-watt output, or fourteen to sixteen Ku-band transponders of 120-watt of output. It would serve to build large-capacity Ku and C dual-band communications satellites, Ku-band direct-broadcast satellites, and tracking and data relay satellites.
As payloads are the core of a satellite and the decisive factor in determining its uses and performances, and as the technical level of Chinese payloads was much lower than that of advanced countries, China must develop or acquire critical payload technologies on a priority basis. The main payloads of a communications satellite are transponders and antennas. In the field of transponders, China must first develop Ku-, L-, S-, and X-band transponders, dual-band (C- and Ku-band) transponders, higher powered transponders, and onboard processing techniques. In the field of antennas, China first must develop multibeam antennas, controllable spot-beam antennas, changeable-shaped-beam antennas, and a number of other antennas, as well as the techniques of onboard switching and intersatellite linkage.
By 2000 China had established more than 30,000 satellite TV receiving stations. The coverage of TV programs has reached 80%. The application of communications satellites has directly promoted the rapid development of TV, broadcast, education, post and telecommunications, etc..
The communications satellite is the most important and commercialized field, which has made the widest use of aerospace technology. Since the cost of the development and use of satellite communications is 43% of that of microwave communications, the services of the satellite communications system increased by 15%-20% yearly in recent 20 years and has formed a broad market. For instance, Inner Mongolia Autonomous Region planned to spend more than one billion yuan to erect microwave relay trunk line within 5-8 years to solve the problem of TV reception. But after using satellite TV receiving stations, the region only spent 3-4 million yuan and covered the whole region within about 2 years. The total investment is only 10 million yuan, including cost of the satellite.
By 2011 China had won successes in its high-capacity GEO satellite common platform, space-based data relays, tracking, telemetry and command (TT&C), and other key technologies, showing remarkable improvement in the technical performance of China's satellites and in voice, data, radio and television communications. The successful launch and stable operation of the Zhongxing-10 satellite demonstrated a significant increase in the power and capacity of China's communications and broadcasting satellites. Similarly, the successful launch of the Tianlian (Space Chain)-1 data relay satellite demonstrated China's preliminary capability of both space-based data relays and space-based TT&C.
China steadily promoted the applications of communications and broadcasting satellites, and has brought into being a market of certain scale. It improved its satellite radio and TV network: in 2008 China established a satellite service platform to give every village access to direct broadcast and live telecasts. It also implemented satellite broadcasting and transmissions of China National Radio and China Central Television programs, and one channel program of provincial radio and TV stations, thus greatly increasing the radio and TV program coverage. China has strengthened development of its satellite tele-education broadband network and tele-medicine network, mitigating to some extent the problem of shortage of education and medical resources in remote and border areas. China has also strengthened its satellite capacity in emergency communications, providing important support for rescue and relief work and for major disaster management.
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