The concept of using space military communications systems implemented in the United States, as well as the constantly growing contribution of satellite systems to the solution of intelligence, communication, radio navigation and meteorological tasks in the interests of the US armed forces, is discussed in an article by Alexander KRYLOV and Konstantin KREYDENKO, an expert in the field of military space communications, published in the magazine "Bulletin GLONASS"
In recent years, the United States has substantiated its goals in space in many documents. The most significant of these are the US Space Command Plan for the period up to 2020 (2002); President Obama's Space Doctrine (2010); National Security Strategy in Outer Space prepared by the Ministry of Defense and the Directorate of National Intelligence (2010); "New US military space strategy" (2011).
In 2010, the Joint Chiefs of Staff of the US Armed Forces issued the Joint Vision 2010 (“Full Spectrum Dominance” concept). The central task of space activities in it is determined to achieve and strengthen the unconditional American military superiority and a leading role in outer space.
Recently, there has been an active transformation of the methods of waging war, due, first of all, to the development of information technologies that have transformed the economic and social life of mankind. The nature of the war has changed radically and ultimately comes down to the postulate: everything that can be seen can be attacked, and that which can be attacked will be destroyed.
A new type of warfare has emerged - information warfare, which also includes disabling the enemy's information systems.
A feature of the US space strategy is the focus on the information component of the use of space, since it is information that greatly increases the efficiency of other systems. The United States is gradually shifting its emphasis from strengthening its combat power to using the information space and is striving to dominate in this particular area.
Thus, the "New US Military Space Strategy" characterizes modern space as more and more crowded, competitive and complex. This document explicitly states that the US armed forces will take any active offensive measures to disinformation, disorganization, containment and destruction of the enemy's space infrastructure if it poses a threat to US security.
In turn, the US Strategic Operational Concept "Large-Scale Military Operations" provides for the use of the US and NATO armed forces, including in the form of a strategic aerospace operation (campaign).
It is with the aim of implementing the provisions of these documents that a global information and navigation system is being created, which will be based on more than two hundred spacecraft. This system is already solving strategic and operational-tactical tasks in reconnaissance, command and control of troops, aiming high-precision weapons and providing troops with communications anywhere in the world, and subsequently will participate in ensuring the delivery of strikes from space to ground targets.
In the coming years, the global information and navigation system can be supplemented with thousands of reconnaissance and attack unmanned aerial vehicles for various purposes and satellites - inspectors of outer space. After integration with the global electronic intelligence system, the new supersystem will be quite capable of creating an effective global combat information field.
The contribution of satellite systems to the solution of reconnaissance, communication, radio navigation and meteorological problems is constantly growing.
UNIFIED SYSTEM OF MILITARY SATELLITE COMMUNICATIONS AND US CONTROL
Satellite communication systems play an important role in ensuring the reliable control of the armed forces. The main purpose of satellite communication systems is to provide command and control bodies in a theater of war or in a specific area with reliable, secure communication channels (data transmission) with armed forces groups, tactical formations, individual military units and each soldier. The main qualities of satellite communications that other types of communications do not have are global coverage and the ability to provide communication channels from anywhere in the world in a very short time.
After full deployment, the AEHF system should become one of the key links of a unified information system for global communication and control of state and military organizations and the basis of a space data exchange system between combatants on land and at sea, in the air and in space.
The United States military satellite communications and command and control system also includes the military broadband satellite communications system (DSCS / WGS), the military narrowband satellite communications system (UFO / MUOS), the military data relay space system (SDS) from reconnaissance satellites, and the military narrowband satellite space system. communication (TacSat) for the Navy. The unified space communication and control system includes space-based radar systems (Space Radar-SR) and unmanned aerial vehicles (UAVs), global positioning systems (GPS), space meteorological systems, satellite control systems, control, communications, computer support, intelligence, tracking and surveillance (Command Control Communications Computers Intelligence Surveillance Reconnaissance, C4 ISR) for the situation on land, at sea, in the air and in space.
The military satellite communication systems of Great Britain (Sky Net) have found wide application in the unified information system of global communications and control of the United States; France (Syracuze); Germany (SATCOMBw) and other US allies.
In peacetime and wartime satellites of the global space relay system (Tracking and Data Relay Satellite System, TDRSS) are involved in the united military satellite communications and control system of the United States. The resources of commercial satellite communication systems Intelsat, SES, Eutelsat, Iridium, Globalstar and others, leased by the US Department of Defense, are increasingly used as part of a unified military satellite communications and control system.
US military satellite communications are the backbone of the information infrastructure of the armed forces and, as of early 2013, includes the following systems: MILSTAR / AEHF, DSCS / WGS, UFO / MUOS, TacSat and SDS.
MILSTAR / AEHF SECURED COMMUNICATION SPACE
The MILSTAR secure communications space system is designed to control the US strategic nuclear forces in a nuclear war. For this system, special measures were developed to ensure the autonomy and survivability of spacecraft.
For the purpose of high security of communication lines, the system uses the Ka-, K- and V-frequency bands. These frequency ranges allow the formation of narrow directional beams, which, along with the noise immunity of the channels, also increase the secrecy of communication lines, since the signals are difficult to find, and therefore suppress. The use of special algorithms for coding and signal processing allows us to guarantee very high security of the communication channel. Through the technical means of satellites, intelligence and video information is transmitted, voice exchange and video conferences are carried out.
The MILSTAR system is used not only for strategic nuclear forces, but also provides communication with all types and branches of the US armed forces.
The orbital constellation of the system consists of five Milstar satellites (two Milstar-1 and three Milstar-2) in geostationary orbit. The satellites were developed by Lockheed Martin.
Milstar-1 satellites allow organizing 192 low-speed (from 75 to 2400 bps) communication channels (44.5 GHz - on the uplink and 20.7 GHz - on the downlink) and a cross-communication system with each other at a frequency of 60 GHz. In addition, the spacecraft have four UHF (300 and 250 MHz) AFSATCOM communication channels for the US Air Force and one UHF (300 and 250 MHz) broadcast channel for the US Navy.
Milstar-2 satellites of the second generation allow organizing 192 low-speed (from 75 to 2400 bit / s) and 32 medium-speed (from 4.8 kbps to 1, 544 Mbps) secure communication channels in an extended operating frequency band.
MILSTAR system hardware implements the following functions:
• onboard processing and switching of signals;
• autonomous control of onboard resources;
• cross-spectrum use (receiving a signal through one antenna in one range and retransmitting it through another antenna in a different range);
• inter-satellite communication.
The on-board antenna complex is capable of detecting the direction of active deliberate interference and temporarily blocking or zeroing the radiation pattern in the direction of the interference, maintaining the mode of operation in other directions without losing communication.
In the complex, the technical means of the system provide adaptive, reliable and stable secure communication between fixed, mobile and portable terminals. These technical means have also been mastered in commercial personal satellite communication systems.
According to plans, the operation of the MILSTAR system ends in 2014.
In turn, the AEHF millimeter-wave space system, which is replacing the MILSTAR system, provides a more secure (double key), reliable, tenacious and high-speed, in comparison with the MILSTAR system, the global connection of the highest political and military leadership of the United States with the command of the armed forces, types and families. troops, commanders of strategic and tactical groupings of troops. The AEHF system is used in all theaters of operations, on land, at sea, in the air and in space, in peacetime and wartime, including nuclear war.
The AEHF system should consist of four (according to other sources, out of five) main and one backup satellite in geostationary orbit. AEHF is compatible with low-speed (75 to 2400 bps) and medium-speed (4800 bps to 1.544 Mbps) MILSTAR channels, and also has new high-speed (up to 8.2 Mbps) communication channels …
The data exchange rate in the AEFH system is five times higher than that in the MILSTAR system, which allows users to transmit target designation and high-resolution video images in real time from unmanned aerial vehicles (UAVs) and Earth remote sensing satellites (ERS).
Onboard signal processing was added to the antenna complex with zeroing of the radiation pattern in the direction of the interference (MILSTAR system). The latter provides protection and optimization of the used onboard resources, system flexibility in relation to various consumers in the branches of the armed forces and other users using land, sea and air-based terminals. In addition, spacecraft of the AEHF system have a developed and reliable communication infrastructure with each other (each with two neighboring ones) in the millimeter (V-) frequency range (60 GHz).
The performance data of the MILSTAR and AEHF systems are presented in Table 1.
The AEHF system consists of three segments: space, user and ground. The space segment is an orbital constellation of spacecraft in geostationary orbit with an inter-satellite communication system providing global coverage. The ground segment of the system control is designed to control spacecraft in orbits, control their operational and technical condition and ensure planning and control of the communication system. This segment is built according to the scheme of multiple redundancy and includes a complex of stationary and mobile control stations. Ground-to-satellite links use 44 GHz and satellite-to-ground links use 20 GHz
The payload module of the AEFH spacecraft includes an onboard signal processing and switching system with their conversion from 44 GHz to 20 GHz and an antenna complex. On-board signal processing provides protection and optimization of the on-board repeater resources, system flexibility in relation to system users using land, sea and air terminals.
The antenna complex of the spacecraft includes the following elements:
• global antenna;
• two transmitting phased antenna arrays (PAR) for working with portable terminals, forming up to 24 channels with time division;
• receiving antenna with phased array;
• six parabolic transmitting and receiving antennas on a gimbal for the formation of regional beams;
• two highly directional antennas for tactical and strategic communications;
• two antennas for inter-satellite communication.
Each satellite of the AEHF system, using a combination of PAR and parabolic antennas, forms 194 regional beams.
Satellites are capable of surviving the use of nuclear weapons.
DSCS / WGS BROADBAND SPACE SYSTEM
The strategic communications system (Defense Satellite Communication System, DSCS) of the US Armed Forces provides communications for the highest military-political leadership, joint and special commands with large formations, formations, units (up to the brigade level) and facilities of the armed forces of the US services and arms. In addition, the system solves the tasks of transferring diplomatic, intelligence and state information, including the exchange of data between automated control systems of various levels and their elements.
The constellation includes eight satellites (six working DSCS-3B spacecraft and two in reserve) in geostationary orbit.
Spacecraft of the DSCS-3 series are provided with more reliable protection against electromagnetic radiation of a nuclear explosion than the spacecraft of the first two series, and have broadband, noise-immune communication equipment on board. In addition, they are equipped with a secure telemetry and satellite control command transmission system, which is designed for quick restructuring in the event of intentional jamming. The capacity of one spacecraft is from 100 to 900 Mbit / s.
The satellite payload module includes:
• six independent transponders and one single-channel transponder;
• three receiving antennas (two horns with a coverage area of the entire visible part of the Earth and one steerable antenna);
• five transmitting antennas (two horns covering the entire visible part of the Earth, two steerable antennas and one high gain parabolic antenna in a gimbal).
The payload module of satellites of this series operates in the X-band: 7900–8400 MHz for receiving and 7250–7750 MHz for transmitting. Transponder power - 50 W. Channel bandwidth - from 50 to 85 MHz. The S- and X-bands are used to control the spacecraft and transmit telemetry.
Due to the increase in data traffic in the provision of trunk communication services and new types of services for the armed forces in the Pacific, Atlantic, Indian Oceans and the continental United States, the country's leadership in 2001 decided to develop a new national broadband satellite communications system of the next generation (Wideband Global Satcom, WGS). Therefore, DSCS satellites are being replaced by WGS satellites, which will consist of six satellites.
The WGS satellites are based on the Boeing BSS-702 platform with a 13 kW capacity and an active lifetime of 14 years.
The first WGS satellite was launched in 2007, two more - in 2009, in January 2012 the WGS-4 satellite was launched. The launch of the WGS-5 satellite is scheduled for early 2013 and the WGS-6 for the summer of the same year.
The payload module of the WGS spacecraft includes several dozen transponders and an antenna complex. The antenna complex can form 19 independent coverage areas and includes:
• global X-band antenna (8/7 GHz);
• transmitting and receiving phased antenna arrays, forming 8 coverage zones in the X-band;
• eight narrow-beam and two zonal parabolic transmit-receive antennas on a gimbal for the formation of 10 beams in the K- and Ka-bands (40/20 GHz and 30/20 GHz).
The 30/20 GHz band is intended for the Global Broadcast System (GBS). The global satellite broadband system GBS transmits video, geodetic and cartographic information, as well as weather and other information for formations, units of all branches of the US armed forces. The satellite receiving equipment of the GBS system operates in the Ka-band (30 GHz) and has four communication channels with a data transmission rate of 24 Mbit / s. Downlink data transmission is carried out in the Ka-band (20 GHz).
The throughput of the WGS spacecraft, due to the use of channel switching devices, means of frequency, spatial and polarization separation of signals, and when using GBS equipment, ranges from 2.4 Gbps to 3.6 Gbps.
To manage the target load of WGS satellites, the US armed forces have created four army Communications Control Centers, each of which can simultaneously control the transmission and reception of data via three satellites.
There is only one satellite mission control center, its ground means operate in the S-band.
Following the initial deployment of the WGS system and the launch of the first AEHF satellite, the US Department of Defense decided to phase out the Transformational Satellite Communications System (TSAT).
UFO NARROWBAND SATELLITE COMMUNICATION SPACE (MUOS)
The UFO satellite communication system (FLTSATCOM at the first stage) was created by the US Navy to provide communication between coastal centers with surface and underwater objects, fleet aviation and circular notification of the fleet forces via a special channel. Currently, the UFO system is the main tactical mobile communications system of the US armed forces in the decimeter range. It is widely used by the Department of Defense, the State Department, the President of the United States and the Strategic Command to control the operational and tactical levels of all branches of the armed forces.
The working area of the system covers the continental United States, the Atlantic, Pacific and Indian oceans.
At the beginning of 2013, the orbital constellation of the system included nine UFO spacecraft (eight main and one reserve) in four orbital positions and 2 FLTSATCOM satellites in geostationary orbit. The UFO satellites are based on Boeing's BSS-601 platform. The active life of the spacecraft is 14 years.
All spacecraft are equipped with 11 UHF solid-state amplifiers. They provide 39 communication channels with a total bandwidth of 555 kHz and 21 narrowband audio communication channels with a bandwidth of 5 kHz each, 17 relay channels with a bandwidth of 25 kHz and a fleet broadcasting channel with a bandwidth of 25 kHz.
The last three UFO satellites are equipped with GBS. These kits consist of 4 transponders with a power of 130 W each, operate in the Ka-band (30/20 GHz) and have a bandwidth of 24 Mbit / s. Thus, a set of GBS on one satellite provides 96 Mbit / s transmission.
The UFO system is now being replaced by the promising Mobile User Objective System (MUOS). The development and production of the MUOS satellite communication system is entrusted to Lockheed Martin. The MUOS system will include five satellites (one standby) in geostationary orbit, a mission control center and a communications network control center. Each MUOS satellite has the capacity of eight UFO satellites.
The initial configuration of the communications system will include a ground control complex and two MUOS satellites, the first of which was launched on February 24, 2012. The full deployment of the first stage system is scheduled for the summer of 2013.
The MUOS satellites are based on Lockheed Martin's A2100 platform. The active life of the spacecraft is 14 years.
The MUOS system is built using key civil satellite communications technologies and significantly improves the capabilities of military communications, providing mobile users (from the strategic level to the individual infantryman) in real time telephony, data and video services. The system is focused on the use of the created common user terminals of the Joint Tactical Radio Systems (JTRS) project, compatible with the UFO system.
The satellites operate in the UHF, X- and Ka-bands. The system will provide narrowband military communication channels and data transmission at speeds up to 64 kbps. The total speed of satellite communication channels is up to 5 Mbit / s, which is 10 times higher than that of the UFO system (up to 400 kbit / s).
The payload of the MUOS spacecraft allows for more efficient use of the allocated frequency range, for which the system will implement multiple access with channel assignment on demand. Thanks to the use of modern methods of digital signal processing, new modulation methods and noise-immune coding, the communication system will have higher reliability, security, noise immunity and efficiency of communication.
The most important requirements for the new system are: ensuring guaranteed access, communication in motion, the ability to form communication networks of various purposes and configurations, the combined interaction of communication networks of different forces, global coverage, broadcasting and communication in the polar regions, the possibility of using small-sized portable subscriber terminals.
TACSAT NARROWBAND SATELLITE COMMUNICATIONS SPACE SYSTEM
In 2005, in order to make the military satellite narrowband communication system global, the United States decided to create an experimental communication system on elliptical satellites.
An experimental satellite TacSat-4 was launched for this purpose in September 2011. The orbit of the spacecraft is elliptical with a perigee of 850 km, an apogee of 12 thousand 50 km and an inclination of the orbital plane - 63.4 degrees. TacSat-4 is an experimental intelligence and communications satellite designed by the US Navy Research Laboratory and the Johns Hopkins University Applied Physics Laboratory with contributions from Boeing, General Dynamics and Raytheon. Weight - 460 kg, antenna diameter - 3.8 m.
The purpose of the spacecraft is to provide global secure anti-jamming communications with units on the battlefield (communication on the move, COTM); detection of enemy submarines; communicating to the units of the US Marine Corps and ships of the results of the assessment of the situation and combat orders in the face of strong opposition from the enemy's radio equipment.
The satellite provides up to 10 narrowband communication channels (from 2.4 to 16 kbps) in the UHF range (300 and 250 MHz).
The TacSat-4 satellite also has MUOS equipment with a 5 MHz bandwidth for receiving and transmitting data via MUOS satellites to the GSO.
The testing and operation of the TacSat-4 spacecraft will enable the US Navy to determine the future need for satellites in high elliptical orbit, operating in the system of geostationary satellites.
USE OF CIVIL SATELLITES FOR MILITARY PURPOSES
Today, the US armed forces, along with the fact that they spend large amounts of money on creating their own space communication systems, are increasingly using commercial satellites for communication and intelligence collection. With the growth of military budgets limited and the ongoing global crisis, the government and military structures of the United States and NATO countries are increasingly using the resources of commercial spacecraft, which are much cheaper than specialized military satellite communication systems.
The independence of the development of military and civilian space communication systems is largely artificial, since the main requirement that determines their appearance is the possibility of their operation in outer space. Relatively recently, an understanding of the feasibility of creating dual-use space systems has come. Dual purpose involves the design of the system, taking into account its application for solving both civil and military tasks. According to experts, this helps to reduce the cost of spacecraft production. In addition, the combined use of military and civilian satellite systems significantly increases the stability of communications in the theater of operations.
A vivid illustration of the influence of military structures on the use of commercial satellites during military conflicts is the famous incident during the NATO war with Yugoslavia. During the fighting in the late 1990s, commercial satellite operator Eutelsat turned off Yugoslav national television broadcasts via HotBird satellites.
Similar shutdowns of national television in Libya and Syria were carried out by satellite operators Eutelsat (European operator), Intelsat (US operator) and Arabsat (behind the states of Bahrain and Saudi Arabia).
In October 2012, satellite operators Eutelsat, Intelsat and Arabsat stopped broadcasting all Iranian satellite channels following a decision by the European Commission under economic sanctions. In October-November 2012, Euronews' news programs broadcast via Eutelsat satellites were interfered with.
In the United States, mechanisms have been worked out for transferring information received from military space systems to civilian agencies, as well as mechanisms for attracting civil and commercial space systems to solve military problems. The US and NATO armed forces in Afghanistan and Iraq make extensive use of commercial satellite systems Iridium, Intelsat, Eutelsat, SES and others. Government (military) orders from Eutelsat have continued to grow with the largest annual gradient (GAGR) among other applications in recent years, which in 2011 accounted for 10% of the company's total revenues.
SES (Luxembourg) and Intelsat have established separate divisions to work with military clients, and revenues from military orders in their total revenues in 2011 amounted to 8% and 20% of their annual revenues, respectively.
Intelsat has invested in UFH payloads for Intelsat 14, Intelsat 22, Intelsat 27 and Intelsat 28 satellites. One of them (Intelsat 22) was created for the Australian Department of Defense, and three more for government, including the military, US organizations.
Launched on November 23, 2009, the Intelsat 14 satellite in the interests of the US Department of Defense installed an Internet Router in Space (IRIS), which physically unites the data transmission networks of the US Department of Defense. In March 2012, the Intelsat 22 satellite was launched, on which, in the interests of the Australian Ministry of Defense, 18 narrowband communication channels (25 kHz) in the UHF range (300 and 250 MHz) were installed in the payload. These channels will be used by the Australian land, sea and air forces for mobile communications. The Australian Department of Defense acquires the full capacity of the UFH range and may use it as it sees fit, including for sale to other consumers.
The Intelsat 27 spacecraft is slated for launch in 2013 and is being built by Boeing based on the BSS-702MP platform. In the interests of the US Department of Defense, this satellite has 20 narrowband communication channels (25 kHz) in the UHF range (300 and 250 MHz) as part of the payload. The UHF payload is similar to that of the UFO-11 military communications satellite and is designed to operate in secure, low-speed military communications systems such as UFO and MUOS.
In September 2011, the first standardized additional payload for remote sensing of the Earth, a CHIRP sensor (Commercially Hosted Infrared Payload), was launched on board the SES 2 satellite by SES. CHIRP was commissioned by the US Air Force to detect missile launches and installed by Orbital Sciences Corporation on the SES 2 satellite. satellite systems of global communication.
Currently, SES is working with government and military structures of a number of countries around the world to use the capacity of the company's satellites in theaters of operations and to include additional payloads (communications and CHIRP) for military and special applications in the satellites under construction. The US government and the US Department of Defense will remain one of SES's most important customers over the next few years.
In the near future, the governments of European countries plan to significantly increase the use of SES space vehicles in the interests of organizing military and special communications to ensure the daily activities of military and other structures in zones of tension and military conflicts (Afghanistan, Iran, the Middle East, etc.).
Telesat is building the Anik-G X-band payload for the future use of its capacity by the military.
Telesat and Intelsat are heavily investing in X-, UHF- and Ka-band payloads because these bands are the most widely used by the military. This segment of the satellite services market is one of the fastest growing in the world. The United States, NATO countries and the countries of the allied alliance of the international armed forces, performing military and peacekeeping tasks in Iraq, Afghanistan, North Africa and Asia, are actively leasing the capacity of commercial (civil) communication and broadcasting satellites to support peacekeeping and theater operations.
In addition, the demand for this type of service was provoked by the adoption of the doctrine, which assumes the active use of video surveillance systems (space and ground) and unmanned aerial vehicles during the operations of the armed forces.
The United States has already worked out mechanisms for transferring information received from military space systems to civilian agencies, as well as mechanisms for attracting civil and commercial space systems to solve military problems. The US Department of Defense receives a large amount of information from civilian Earth remote sensing (ERS) satellites, geodesy and meteorology.
The US military structures use more than 20% of the information received from the civilian remote sensing systems of the USA, France and Japan.
The US Department of Defense's Cartographic Office is the second largest agency after the USDA in terms of the number of purchased images from the Earth remote sensing spacecraft. The interaction of the leading coordinators of the development of new technologies of military and civilian departments (DARPA, NASA, etc.) has also been organized in the form of joint projects and bilateral agreements on the coordination of work in the field of new technologies. The United States is a leader in the use of military space systems for civilian purposes and commercial satellites for military purposes.
Recently, the trend of using civil (commercial) space systems for military purposes has been increasing. For example, during the US military operation in Iraq and Afghanistan, up to 80% of military communications in the theater of operations were provided by commercial satellite systems (Iridium, Intelsat, etc.). About a third of the 30,000 shells and bombs fired into Iraq were guided by a satellite-based global positioning system (GPS).
Potential candidates for satellites - carriers of ERS payloads are spacecraft of the global mobile communications system IRIDIUM NEXT (launch of the spacecraft in 2014). The advantages of associated payloads are a radical reduction in their cost, even in comparison with small-sized vehicles.
The new tendency has taken shape also organizationally. In 2011, the United States formed the Hosted Payload Alliance, a non-profit organization that brings together developers, payload owners, and operators.
CONCLUSIONS
1. Systems of military satellite communications of the United States are united into a single global satellite broadcasting system GBS, which transmits all types of data and information for formations, units and military personnel of all branches of the armed forces. The GBS system implements a hierarchical addressing system with automatic address reconfiguration, as well as direct connections and connection of single user terminals such as JTRS.
2. In the near future, in the US armed forces, any formation or unit, each serviceman, item of military equipment or weapons will have its own unique address. This address will allow real-time monitoring of the position and state of all elements of the situation - to form a single digital picture of the combat space with the necessary information security measures. In order to misinform the enemy, these addresses can be changed.
3. The US Armed Forces are integrating satellite communication systems, navigation satellite systems, geodetic satellite systems, space meteorological systems, missile attack warning systems, Earth remote sensing systems, and satellite and aircraft reconnaissance systems into a single satellite network. The unified satellite network will include more than two hundred satellites for military, dual and civil purposes, which will be used to support combat operations in the theater of operations.
4. In the context of limiting the growth of military budgets and the ongoing global crisis, the government and military structures of the United States and NATO countries are increasingly using the resources of commercial spacecraft, which are much cheaper than specialized military satellite communication systems.
