The TT&C communication system of the first phase of China's lunar exploration project will be based on the existing unified S-band (USB) space TT&C network and the very long baseline radio interference network (VLBI system) of China Observatory, and through appropriate technical transformation, it will meet the telemetry, remote control, orbit measurement and navigation tasks of the "Chang 'e 1" lunar probe in each flight stage.
So what is a unified S-band (USB) TT&C network?
Unified S-band (USB) space TT&C network refers to a unified microwave TT&C system using S-band. The unified microwave measurement and control system here refers to a radio measurement and control system that integrates the functions of spacecraft tracking, orbit measurement, telemetry, remote control and communication between heaven and earth. The basic working principle of microwave unified system is as follows: first, all kinds of information are modulated on subcarriers with different frequencies, and then * * * modulation is transmitted on one carrier; At the receiving end, the carrier is demodulated first, and then the subcarriers are separated by filters with different frequencies; Demodulate each subcarrier signal to generate the original information during transmission. Microwave unified measurement and control system generally consists of antenna tracking/angle measuring system, transmitting system, receiving system, telemetry terminal, remote control terminal, ranging/speed measuring terminal, time/frequency terminal, monitoring system, remote monitoring or data transmission equipment and other auxiliary equipment.
The unified S-band (USB) TT&C network was first used in the United States in the 1960s, when the Apollo moon landing program was implemented. In the early 1960s, when the United States carried out manned space missions of Mercury and Gemini, various frequency bands of equipment were used for different missions. As a result, the spacecraft has many antennas, heavy weight and poor reliability, and the earth is equipped with very complicated equipment accordingly. In order to change this situation, NASA put forward a unified S-band (2000 ~ 4000 MHz) system as the ground support system for Apollo's moon landing program, and built a measurement and control network with unified S-band as the main body in the mid-1960s, thus upgrading the space TT&C system from a single-function decentralized system to a comprehensive multi-functional system.
The TT&C system of spacecraft in China has also experienced the development stages from land to sea, from domestic to foreign, from single system to multi-band and multi-system. At present, TT&C network, which used to monitor only a dozen satellites at the same time, has developed into TT&C management that can handle dozens or even hundreds of spacecraft calmly, forming a modern comprehensive TT&C network with Xi 'an Satellite TT&C center as the center and more than ten fixed stations, mobile TT&C stations and Roy survey ships as the backbone. In manned spaceflight project, China's spacecraft measurement and control system adopts a unified S-band system, which sends or receives telemetry and remote control signals, voice and television signals through the same transmitter, antenna system and receiving equipment. The TT&C communication system of China's lunar exploration project will meet the telemetry, remote control, orbit measurement and navigation tasks of "Chang 'e 1" lunar probe in each flight stage through appropriate technical transformation on the basis of the existing unified S-band, so that the distant "Chang 'e 1" can hear the voice of hometown and feel the affection of relatives.