How is the Milstar military satellite communication system composed?

According to the original plan, the Milstar constellation consists of eight satellites, five of which are located above the equator, one of which is an in-orbit backup satellite, and the other satellites are located at latitudes with higher or lower polar coverage. However, due to different opinions from all walks of life in the United States on the original plan, the US Department of Defense suggested reducing the number of satellites in 1990, and the plan for six Milstar satellites was made in 1994. Milstar satellite communication system adopts EHF frequency band, with uplink frequency of 44GHz and downlink frequency of 20GHz, and the bandwidth can reach 2GHz. Compared with UHF band, EHF band has the characteristics of large global coverage and few radio blind spots. In addition, it also has an interstellar link from satellite to satellite, thus shortening the communication distance; And its frequency is high, frequency bandwidth, anti-jamming and anti-interception performance is good; It also has the advantage of small antenna.

Using diversified antennas on satellites can further improve the anti-jamming ability. One is to use a high-gain universal sharp directional beam antenna to emit a well-defined spot beam, which can provide good communication for the special area of the maritime task force. Because of the high gain of the antenna, it is possible to use the smallest terminal; There is also a fast scanning multi-beam array antenna, which can be used for anti-jamming communication with high gain and low sidelobe around the world. The antenna adopts antenna zeroing technology, which can null the beam in the direction of enemy interference, thus further enhancing the anti-jamming ability in the jamming environment.

There is a platform processor on the satellite, which despreads, demodulates and decodes each received channel signal, and then transmits it to the ground terminal after the above-mentioned inverse process. There is a whole set of computers on the satellite, which can automatically control multi-channel communication resources through "first-in-first-out" without the implementation of the ground network control station.

The timing of the whole communication system is based on the atomic standard clock of the constellation. In order to ensure the synchronization of newly registered terminals in the network, the satellite provides detection response. There is also a mission control unit on board, which adopts artificial intelligence technology and can be reassembled and repaired through its own redundant control. Even if the ground mission control station is destroyed, the satellite can still work normally for about 6 months without ground intervention.

There is a large amount of propellant stored on the satellite, which can be maneuvered to change orbit when attacked. The medium data rate (MDR) channel of 1.544Mb/s/s was opened in the transponder, which coexisted with the low data rate (LDR, 75b/s ~ 2.4 KB/s). The MDR channel transmits a standard theater air combat command in less than 7 minutes, and sends cruise missile target correction data to warships in less than 10 second, which is very beneficial to seize the operational opportunity.

Inter-satellite communication adopts 60GHz frequency band, without multi-hop or ground relay, which is vulnerable to enemy attacks. Two multiple access technologies are adopted, frequency division multiple access and full-band frequency hopping are adopted in the uplink, and time division multiple access and fast frequency hopping are adopted in the downlink. The information transmitted by satellite is encrypted and advanced error correction technology is adopted. Even if nearly half of the bits are scrambled or lost, the error-correcting code can still recover the information. Each satellite can have 50 EHF channels and 4 SHF channels.

With regard to the ground part of the satellite system, under the leadership of the Joint Terminal Equipment Planning Office of Milstar Satellite Communication System, the armed forces have designed and developed a series of indestructible and interoperable terminal equipment. The Milstar ground terminal planned by the US Navy is used to supplement and replace UHF equipment. A /USC-38 (V) terminal will be used, which can work at medium data rate. According to practical application, antennas with different diameters will be configured, such as shore station 1.8m, ship station 87cm and submarine periscope 14cm. As for the key components in the terminal, including antenna feeder, compass, rubidium frequency reference clock, synchronizer and 5W and 10W solid-state power amplifiers, the Army requires all contractors to make backup configurations.