1、 The U.S. military puts forward a vision for the future development of satellite communication architecture

Figure 1. US space force's vision for satellite communications

2、 The US Department of Defense issued the 5g strategy to accelerate the development and deployment of 5g technology

In May 2020, the U.S. Department of Defense issued the 5g strategy, which is the first 5g strategic guidance document publicly released by the U.S. military. 5g is identified as the "key strategic technology" to establish and control military advantages, and it is proposed to develop sub-6 and millimeter wave 5g technologies at the same time.

The strategy points out the main problems faced by the Department of Defense's 5g development, that is, while accelerating the development and deployment of 5g capabilities, ensure that these systems and U.S. allies and partners' systems are robust, protected, resilient and reliable. It defines the 5g development goal of the Ministry of defense, that is, to develop a secure and tenacious 5g capability, ensure the use of global spectrum resources, form a reliable microelectronic supply chain, and cooperate closely with international partners in 5g development and protection. Four main lines to promote 5g development are determined. First, promote technology development, focus on 5g demonstration, promote the development of millimeter wave technology, promote dynamic spectrum sharing, implement open architecture and virtualization, and deepen talent development; Second, assess and reduce 5g vulnerabilities, overcome them, and operate 5g, focusing on key areas such as threat intelligence, minimizing 5g infrastructure risks, supporting the global operations of the U.S. Department of defense, security assessment, and network security and zero trust; Third, influence 5g standards and policies, including implementing the "standard participation plan", actively participating in 3GPP organization, providing greater spectrum access, capacity and anti-jamming capability, developing new operational concepts, taking the lead in using 5g revolutionary speed and connection capability, and protecting 5g enabling technology from potential adversaries of the United States through technical control measures; Fourth, attract partners, mainly including international allies and partners, including industry and Congress.

The U.S. Department of defense officially raised the 5g R & D deployment to the strategic level, and promoted the implementation of multiple initiatives, including 5g application tests at multiple military bases and launching 5g network security research projects, which fully reflects its determination to develop and apply 5g technology to upgrade key infrastructure and improve combat effectiveness.

3、 The deployment of the U.S. military's "advanced extremely high frequency" communication constellation has been completed

Figure 3. Us "advanced extremely high frequency" satellite

On March 27, 2020, the United States joint launch alliance successfully launched the sixth advanced extremely high frequency (aehf-6) military communication satellite of the US space force from launch pad 41 of Cape Canaveral Air Force base, Florida, using the atlas V551 carrier rocket. Aehf-6 satellite is built by Lockheed Martin company and the payload is provided by Northrop Grumman aerospace systems company. It is the last satellite of the "advanced extremely high frequency" satellite constellation. This launch marks the formal completion of the constellation. The on orbit test of aehf-6 was completed at the end of August 2020. The US space force officially obtained the control of aehf-6 on October 29, 2020 and announced that the control was transferred to the space operations command on December 4.

AEHF system is the successor of Milstar system, which can provide protected anti-jamming satellite communication for high priority military assets of the United States and its allies. The constellation has strong survivability and can be used for strategic and tactical purposes to achieve key nuclear command and control capabilities and strategic communication capabilities. AEHF enables strategic and tactical users to communicate globally over high-speed networks, providing protected communications in any environment, including real-time video, battlefield maps and target targeting data. In addition, it can also provide relevant services to American international partners such as Canada, the Netherlands and the United Kingdom.

4、 The US Department of defense launched the construction of the next generation "Defense Space Architecture" transport layer

In May 2020, the US space development agency issued the work description of space "transport layer 0", which defined the basic composition, development plan, main objectives and key areas of the "transport layer 0" constellation of the next generation "National Defense Space Architecture"; In August, Lockheed Martin and York space systems were awarded contracts to build 10 satellites for "transport layer 0" respectively, which are expected to be launched before September 2022.

"National Defense Space Architecture" is a new space architecture based on distributed LEO constellation, which is composed of seven levels. The "transmission layer" is the transmission backbone of the whole architecture and the basis of other layers. It will provide military data and connectivity with guarantee, toughness and low delay for the global combat platform of the U.S. military. The space segment of "transport layer 0" is a low orbit constellation composed of 20 satellites, which uses optical inter satellite links to form a mesh network, uses the link 16 data link widely used by the US military services and allies to connect ground users, and can connect the "integrated broadcasting system" (IBS) with UHF Communication capability and compatible with the application system of the intelligence community.

The transport layer of the "Defense Space Architecture" will form the space part of the joint global command and control (jadc2) of the US Department of defense, which is a key part to connect space-based sensors and ground shooters. Through this architecture, NASA will ensure that space-based sensor data can be sent to the battlefield networks of various services in near real time, so as to realize the concept of joint global command and control.

5、 US Army promotes the modernization of tactical network through "capability set" iteration

6、 The United States has developed spaceborne Link16 data link terminal

Figure 6 # effect diagram of link 16 antenna of roccor company in the United States

In May 2020, roccor developed a deployable L-band satellite antenna that can receive and transmit link 16 signals. It will be carried on the low orbit small satellite developed by viasat for the U.S. air force to verify the feasibility of using link 16 on the low orbit small satellite. The antenna is a spiral body with a deployable RF aperture of two meters. It adopts the slit tube synthetic suspender technology. It can be carried on a cube satellite with a size of 2U and deployed in orbit after the satellite is launched.

Link 16 is the most widely used data link in the U.S. military. Without on-board terminal, link 16 data link can realize line of sight extension through satellite, but it only uses satellite as an "information repeater", which has great limitations in real-time, integrity and security of information transmission, and can not support the needs of real-time joint operations. The spaceborne link 16 terminal can realize more efficient over the horizon connectivity and greatly improve the flexibility and coverage of the link 16 data link. According to the plan of the U.S. military, in the future, the LEO satellite equipped with link 16 terminal will form a constellation to achieve global coverage. At that time, the terminals used by low-level forces at the tactical edge will be able to directly access the satellite, so as to obtain more flexible and diverse communication access means. In addition, with the help of the new Internet satellite constellation or the traditional broadband geostationary earth orbit satellite constellation, by adding the capabilities of the network layer and above for link 16 (link 16 itself only has the capabilities below the data link layer), its connectivity flexibility is further improved, and functions such as routing and switching can also be realized on the link 16 data link.

7、 "Star chain" Internet constellation is deployed on a large scale and has commercial service capability

In 2020, the "star chain" Satellite Internet plans to complete 14 satellite launches and 16 launches since 2019. With the two test satellites launched in early 2018, the total number of launched satellites has reached 955. Excluding passive orbit attenuation and active orbit departure, the number of on orbit satellites is about 900, becoming the largest satellite constellation in the world.

SpaceX launched the "better than nothing" commercial service test of "star chain" for users in the north of the United States, and said: the test feedback is good, "people are enjoying a fast speed and a short time delay", which indicates that the "star chain" constellation has commercial service capability. The company is expanding testing to Canada. Before the test, the "star chain" team said that the network data transmission speed is expected to be between 50 ~ 150Mbps and the network delay is controlled at 20 ~ 40ms.

VIIIDARPA develops distributed mosaic antenna to support the landing of mosaic warfare concept

On June 5, 2020, DARPA launched the "resilient networked distributed mosaic communication" (RN DMC) project, which aims to develop distributed low-size, weight, power and cost transceiver units, or "tiles", to form mosaic antennas to replace high-power amplifiers and large directional antennas to provide remote communication. The transmission power will be distributed over multiple fragments and the energy will be concentrated through signal processing rather than using physical antenna aperture to obtain gain. These debris can be carried by ground platforms, including handheld devices carried by soldiers and Marines, autonomous aircraft, high-altitude platforms and low-cost / low earth orbit satellites.

The advantages of this mosaic antenna are: on the one hand, it uses distributed beamforming and distributed coherent radio technology to improve the coverage of the antenna system and realize omnidirectional, high data rate, long-distance and high reliable communication; On the other hand, the power distribution in the coverage area is dynamically adjusted through the multi antenna structure to reduce the overall power consumption of the system and realize flexible networking. DARPA believes that the rndmc plan can fundamentally change the long-range tactical communication method and support the implementation of the "mosaic war" concept.

9、 DARPA successfully demonstrated heterogeneous data link interconnection technology in countermeasure environment

10、 DARPA's "Black Jack" LEO communication and Monitoring Constellation plan is accelerated

On June 10, 2020, DARPA awarded three "Black Jack" LEO communication and surveillance constellation project contracts to blue Canyon, SA Photonics and Raytheon, respectively, a satellite platform contract worth US $14.1 million, an optical communication payload contract worth US $16.3 million and a missile early warning satellite payload contract worth US $37 million. By the end of 2020, the two test satellites of the "Black Jack" project, "mandelac 1 and 2", had been developed and ready to be launched by SpaceX company, but they were damaged during assembly with the rocket and could not be launched as scheduled. Mandelac 1 is a cube satellite that will test the performance of supercomputer processing chips in space environment; Mandelac 2 is a pair of small satellites, which will carry optical inter satellite links for broadband data transmission, which is very important for the construction of on orbit mesh network.

DARPA "Black Jack" project was launched in 2018 to develop a constellation composed of 60 ~ 200 satellites, which operates in low earth orbit with an altitude of 500 ~ 1300 km, forming a global high-speed network backbone network in low earth orbit. The whole system is operated by a single operation control center and can operate independently on orbit for 30 days. Each satellite operates independently, sharing data and cooperating with each other. The satellite carries various payloads such as communication, ground surveillance and missile early warning. It is highly networked, flexible and persistent. It can provide over the horizon sensing capability, signal transmission and communication capability, so as to provide all-round coverage and constant monitoring services of the world's sea, land and air.

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