Space Laser Communication Technology

In 2017, NASA will launch the Laser Relay Relay Demonstration Satellite (LCRD), a two-way laser communication link between GEO (geosynchronous orbit) satellites and ground stations, a ground station-GEO-ground station , It is desirable to achieve a communication rate of up to 2.88 Gbps between the geosynchronous orbit and the ground station. At the same time, the United States in the 500mw laser pointer communication network put forward a series of plans. In 2010, the Satellite Telecommunications Program (TSAT) was put forward to integrate the satellite communication, inter-satellite communication, satellite communication and air-to-air communication into the communication network, and transform the existing microwave communication to laser communication. In 2014, the United States began to study "satellite-ground global hybrid optical network communication technology", based on the Earth orbit laser communication system, integrated space optical communication and ground and submarine optical fiber communication network, in order to achieve 4.8Tbit / s inter-satellite laser communication Speed ​​and 200Jbit / s satellite-to-bi-directional laser communication. Japan plans to launch in 2019, "Laser Data Relay Satellite", the current data relay system to replace the microwave link to the laser link, the default communication rate of 2.5Gbit / s; August 16, 2016, the world's first One of the payloads was the space high-speed coherent laser communication sub-system, which was successfully launched by the quantum scientific experimental satellite Mozi.

At present, the microwave communications commonly used in the satellite due to carrier frequency constraints, the communication rate in the application has been close to the limit, microwave communication gradually become unable to adapt to changes in the times. Space laser communication is a laser carrier frequency, 100mw laser pointer frequency is high, 3-4 times higher than the microwave frequency, there is a very huge communication capacity, you can easily achieve more than 10Gbps communication rate, the use of multiplexing means to get Tbps Of the communication rate, easy real-time mass data transmission. In addition, the space laser communication also has strong anti-interference ability, strong anti-interception, security, good security, small size, light weight, low power consumption, communication quality is higher.

Acquisition, aiming and tracking are one of the key technologies in space laser communication. From the foregoing description can be seen, the technical difficulty is not generally high ah. Large uncertainty zone, small beam angle, platform vibration and the relative motion between the communication platform are the difficulties to overcome this technology. Atmospheric interference has a great influence on laser communication. Laser beam through the atmosphere when there is loss, turbulence, burning laser pen wavefront distortion, etc., not only affect the communication rate and communication results, even when serious communication. The transmission distance of space laser communication is thousands of meters and tens of thousands of kilometers, so the laser can produce very large energy loss in such long distance transmission. The received light signal is very weak. In addition, the background light (sun, Moon, stars, etc.) will also have a strong interference, greatly increasing the difficulty of receiving optical signals. The characteristics of laser determines the space laser communication between point and point for the safety of communication, networking requires a large area coverage is also more difficult.

Simply point out that space laser communication is the information through the modulation of the electrical signal is loaded on the laser, both ends of the communication through the initial positioning and adjustment, and then after the capture of the beam, aiming, tracking the establishment of dynamic optical communication link, Vacuum or atmospheric channels. Space laser communication systems are extremely complex. It includes light source systems, transmit and receive systems, beacon systems, capture, aiming, tracking (APT) systems, and other ancillary systems. Among them, the capture, aiming, tracking (APT) subsystem is a space2000mw laser pointer communication system specific to the system. APT sub-system is mainly responsible for the establishment and maintenance of space laser communication link, because the space laser communication terminal beam divergence angle is very small, for the micro-arc magnitude, which APT system put forward very high requirements, aiming accuracy of 1μrad . The accuracy of the Japanese scholars have been observed in Tokyo, Japan, Mount Fuji observation of a moving needle on the needle.

Space laser communication links a total of six categories: inter-satellite laser communications, satellite laser communications, space laser communications, air-to-air laser communications, air-ground laser communications, ground laser communication. The interchannel laser communication link channel is a free space channel, without the interference of atmosphere, weather and other factors, it is the most suitable application of laser communication. Therefore, all countries choose interstar 50mw laser pointer communication link as the entry point of laser communication in space application. . Compared with the inter-satellite laser communication link, the laser signal of star-earth laser communication needs to experience the influence of free space, atmospheric turbulence random channel, cloud, rain, haze and other meteorological conditions to achieve high reliability and high usability. But the spatial data must be transmitted to the ground eventually, so the satellite laser communication technology is the bottleneck of the current space laser communication, is also the focus of the current research and difficult.

Space laser communication research has been carried out for many years, but until recent years, technology breakthroughs and bandwidth enhancements to really promote space laser communication into the application phase. European Data Relay System (EDRS) Program: On 30 January 2016, ESA successfully launched a communications satellite, EDRS-A, which provides two-way inter-satellite links between laser and Ka-band, with inter-satellite transmission rates 1.8 Gbit / s. The EDRS program is the first commercial high-speed space laser communication system, marking the space laser communication from the technical demonstration to the application phase. The EDRS program involves one ground station, two LEO satellites (Sentinel 1A, Sentinel 2), and three high-orbiting satellites (Alphasat, EDRS-A and EDRS-C) that transmit data from near-Earth orbit satellites into the geostationary orbit Following the satellite, and then relay satellite transmission, the data back to the ground. ESA intends to launch EDRS-C by mid-2017, which will provide only high power laser pointer links. And in 2020 to add a third satellite "global network" (GlobleNet), in order to achieve global data relay service.

Space laser communication will bring the revolution in communications, I believe in the near future, we will be able to enjoy the convenience of space laser communications.