Future U.S. Military Satellite Communication Systems

Glen Elfers and Stephen B. Miller

The current military satellite communications network represents decades-old technology. To meet the heightened demands of national security in the coming years, newer and more powerful systems are being developed.

Advances in information technology are fundamentally changing the way military conflicts are resolved. The ability to transmit detailed information quickly and reliably to and from all parts of the globe will help streamline military command and control and ensure information superiority, enabling faster deployment of highly mobile forces capable of adapting quickly to changing conditions in the field. Satellite communications play a pivotal role in providing the interoperable, robust, "network-centric" communications needed for future operations.

In 1997, the Senior Warfighters' Forum established a road map charting the course of military satellite communications through 2010. In 2002, there will be course corrections as the Department of Defense pursues an aggressive acceleration in the delivery of improved communications capability.

Military satellite communications (or milsatcom) systems are typically categorized as wideband, protected, or narrowband. Wideband systems emphasize high capacity. Protected systems stress antijam features, covertness, and nuclear survivability. Narrowband systems emphasize support to users who need voice or low-data-rate communications and who also may be mobile or otherwise disadvantaged (because of limited terminal capability, antenna size, environment, etc.).

Milsatcom is a system of systems that provides balanced wideband, narrowband, and protected communications capability for a broad range of users across diverse mission areas. The anticipated implementation of advanced architectures, supported by heightened connectivity in space as well as on the ground, will enable national security space communications to take advantage of commercially developed Internet-like communications, but with greater assurance and security.

For wideband communication needs, the Wideband Gapfiller Satellite program and the Advanced Wideband System will augment and eventually replace the Defense Satellite Communications System (DSCS). These satellites will transmit several gigabits of data per second—up to ten times the data flow of the satellites being replaced. Protected communications will be addressed by a global extremely high frequency (EHF) system, composed of the Advanced Extremely High Frequency System and Advanced Polar System. These systems are expected to provide about ten times the capacity of current protected satellites (the Milstar satellites). Narrowband needs are supported by the UFO (Ultrahigh-frequency Follow-On) constellation, which will be replaced by a component of the Advanced Narrowband System (see Milsatcom Timeline).

Capacity gains in these systems will also be matched by improved features, such as multiple high-gain spot beams that are particularly important for small terminal and mobile users. Satellite, terminal, control, and planning segments will utilize emerging technology to ensure the best capability for the cost. Coordination among ground, air, and space segments and between government and commercial assets will help ensure deployment of the most efficient, effective, and affordable communications systems.

The Wideband Gapfiller Satellite program will provide the next generation of wideband communications for the Department of Defense. (Boeing Satellite Systems)

Wideband Communications

Assured capacity is the primary goal of the military's wideband communications sector. Wideband data rates are defined as those greater than 64 kilobits per second, although the line between wideband and narrowband is blurring as commercial data rates to disadvantaged users move higher. The military's wideband requirements are currently supported by DSCS and the Global Broadcast Service, as well as commercial systems. These military systems, together with the planned Wideband Gapfiller satellites, will form the Interim Wideband System, which will eventually give way to the Advanced Wideband System.

Wideband Gapfiller Satellites

The Wideband Gapfiller Satellite program will provide the next generation of wideband communications for the Department of Defense (DOD). The constellation will supplement the military X-band (roughly 7–8 gigahertz) communications capability now provided by the Defense Satellite Communications System and the military Ka-band (about 20–21 gigahertz down, 30–31 gigahertz up) capability of the Global Broadcast Service. In addition, the Wideband Gapfiller Satellite program will include a high-capacity two-way Ka-band capability to support mobile and tactical personnel.

The name "Gapfiller" is somewhat misleading because this very capable wideband communication payload will include state-of-the-art technology and provide a major leap in capability. Preliminary estimates indicate that one Wideband Gapfiller spacecraft will provide transmission capacity up to 2.4 gigabits per second. This capability alone exceeds the capacity of the entire existing DSCS and Global Broadcast Service constellations.

Throughput capacity is divided among nine X-band beams and ten Ka-band beams. Eight of the X-band beams are formed by separate transmitting and receiving phased-array antennas, which provide the ability to shape and scale coverage areas. The ninth X-band beam provides Earth coverage. The ten Ka-band beams are formed by gimbaled dish antennas and include three beams with reversible polarization. (Polarization—the direction of the electric field of an antenna—plays an important part in optimizing reception or reducing the effects of jamming).

The military satellite communications framework is a system of systems that provides connectivity for a broad range of users across diverse mission areas. In the future the framework will support "network-centric" warfare through an architecture that promotes the interconnection of satellites and constellations in space, as well as through ground nodes.

The key to the very flexible payload is the digital channelizer (or digital signal processor). The channelizer divides the communications capacity into 1872 subchannels of 2.6 megahertz each and switches and routes these subchannels. The signals can be cross-banded from one frequency band to another and any uplink coverage can be connected to any downlink coverage. Also, any uplink signal within one coverage area can be connected to any or all downlink coverages.

The implementation plan calls for a minimum of three geosynchronous spacecraft and associated ground control software, with an option for up to three additional spacecraft. The payload will be integrated into a commercial spacecraft bus. Each satellite will weigh approximately 5900 kilograms at launch and use more than 10,000 watts of power. This design uses bipropellant chemical propulsion for orbit raising and xenon ion propulsion to remove orbit eccentricity and for station keeping. The mean mission duration for each spacecraft is 11.8 years.

The Defense Satellite Communications System (DSCS) is part of the Interim Wideband System, along with the Global Broadcast Service and the Wideband Gapfiller System. (Lockheed Martin Missiles and Space)

Synchronization of the various Wideband Gapfiller Satellite segments is under way, and 1700 operational wideband terminals are expected by 2010. Terminals capable of operating within several frequency bands are a fundamental piece of the wideband architecture, and a recent contract awarded to Harris Corporation for up to 200 lightweight, high-capacity quad-band Ground Multiband Terminals (GMTs) will help ensure the delivery of communications services through the Wideband Gapfiller satellites, as well as through the current DSCS, future Advanced Wideband System, and commercial satellite systems. Also, the Army's Multiband/multimode Integrated Satellite Terminal (MIST) will provide up to megabits-per-second capacity for mobile communications in the next decade.

Responsibility for control of the satellites will be shared among various branches of the armed services. Network control will rely on existing worldwide ground facilities operated by the Army. Spacecraft control will be conducted by Air Force operators using the Command and Control System—Consolidated (CCS-C). The CCS-C is the integrated command and control system being developed to support all milsatcom satellite constellations, legacy and future. It will replace the current command and control functions of the Air Force Satellite Control Network.

The Wideband Gapfiller Satellite contract was awarded to Boeing Satellite Systems in January 2001, and the first satellite launch is planned for the second quarter of fiscal year 2004—just three years after the contract award.

Through the Global Broadcast Service, information such as video, maps, charts, weather patterns, and digital data can be transmitted to mobile users equipped with small tactical terminals.

Global Broadcast Service

Operation Desert Storm clearly demonstrated the need for the rapid delivery of large volumes of information to users on the front lines. During Desert Storm, air-tasking orders and intelligence reports were sometimes delivered by hand due to the lack of available communications bandwidth. This concern drove the creation of the Global Broadcast Service in the mid-1990s. With the advent of this service, most critical information could be transmitted in seconds. For example, a 1-megabyte air tasking order that might take up to an hour to transmit over Milstar or UFO (at 2.4 kilobits per second) could now be sent in less than a second. The ability to push megabits of data to a small terminal was made possible by commercial advancements in high-power satellite transponders and direct broadcast service technology. The first, and very successful, use of the Global Broadcast Service was in support of operations in Bosnia in 1996, where commercial satellites were used to broadcast military data to modified commercial direct broadcast set-top receivers and decoders.

Today, the Global Broadcast Service is provided through a series of four Ka-band transponders and three steerable beams hosted on the Navy's UFO 8, 9, and 10 spacecraft. Ground terminals with antenna diameters of 0.6 to 1 meter receive data at rates up to 24 megabits per second per transponder from either of the two 500-nautical-mile diameter spot beams. Rates up to 1.5 megabits per second can be achieved through the 2000-nautical-mile diameter spot beam. Data are uplinked to the transponders through fixed Primary Injection Points and transportable Theater Injection Points. The receiving suites and broadcast-management suites supplied by Raytheon Company support military Ka-band and commercial Ku-band operations.

In the future, the Wideband Gapfiller Satellite will provide the Global Broadcast Service through Ka-band transponders. This is the second hosted Global Broadcast Service implementation, and its migration path is still under consideration with regard to the Advanced Wideband System.

Advanced Wideband System

The successor to the Defense Satellite Communications System and the Wideband Gapfiller Satellite program is the Advanced Wideband System. The system's final configuration has not yet solidified under ongoing milsatcom transformational efforts, but the concept is one of applied technology and engineering that will remove capacity as a constraint on warfare communications. Analyses by the Defense Information Systems Agency and Joint Staff indicate that a global wideband satellite communications capacity in excess of 15 megabits per second will be needed by the middle of the next decade.

The Global Broadcast Service replaces the superhigh-frequency X-band payload with four 130-watt military Ka-band transponders. Each transponder can be accessed through either of the receive paths, configured by ground command. Data are transmitted through three spot-beam antennas on each spacecraft. Two of the beams each cover an area 500 nautical miles in diameter, and the third covers an area of 2000 nautical miles in diameter.

The Advanced Wideband System will take advantage of the commercial and government technology advances of the first half of this decade to meet expected needs. Laser crosslinks, space-based data processing and routing systems, and highly agile multibeam/phased-array antennas will most likely be included. A constellation of advanced wideband-capable satellites is planned with a first launch at the end of this decade.

Capacity in the right place is the overall requirement, but getting adequate capacity to ever-smaller terminals worldwide is becoming increasingly difficult because of the limits on the amount of internationally allocated bandwidth in the X and Ka bands for DOD use (see related article, "Critical Issues in Spectrum Management for Defense Space Systems"). Several options for mitigating the current limitations are under consideration, including the use of higher frequencies (notably in the 40–75-gigahertz range, and possibly much higher). Also, increasing the number of wideband-capable satellites over a region would enable users with directional antennas to use an allocated frequency band on more than one satellite in view. Another approach would increase effective bandwidth by simultaneously reusing allocated frequencies through the use of small independent beams or cells, achievable through multibeam/phased-array antennas. Frequency reuse is an important characteristic of terrestrial and space-based cellular systems. Radio-frequency components with more efficiency and power will also be used to get more data to small terminals, similar to the way commercial direct broadcast service transponder technology was adopted for the Global Broadcast Service a decade earlier.

Synchronization of the various Advanced Wideband System segments is beginning. To support these efforts, new terminals, such as the GMT, will be introduced, and the CCS-C will be employed, but with significant additional capability to address the increased complexity in providing high capacity, tailored communications to highly mobile forces.

Protected Communications

Protected systems have the ability to avoid, prevent, negate, or mitigate the degradation, disruption, denial, unauthorized access, or exploitation of communications services by adversaries or the environment. Future protected systems include the Advanced Extremely High Frequency System and Advanced Polar System.

Advanced EHF

The loss of Milstar Flight 3 in 1999 and the last deployment of a Milstar satellite (Flight 6) in fiscal year 2003 have increased the need for a successor system with full operational capability by 2010. Consequently, in November 2001, the Advanced Extremely High Frequency (AEHF) System contract was awarded to the Lockheed Martin Space Systems and TRW Space and Electronics team for the System Development and Demonstration phase of the new program. Under this contract, three satellites and the associated ground command and control segment will be produced. Under DOD transformational initiatives, other protected milsatcom options are being considered to complete the needed protected strategic and tactical capability; however, if full operational capability cannot be achieved in time with the transformational options, then the original program to acquire four AEHF satellites plus one spare will be restored. All new protected satellites will be interoperable with the Milstar satellites.

Milstar provides protected communications and offers advanced features such as onboard signal processing and satellite-to-satellite crosslinks. The system will eventually give way to the AEHF system. (Lockheed Martin Space Systems. Photo by Russ Underwood)

The AEHF System will have up to 12 times the total throughput of Milstar, in some scenarios. Single-user data rates will increase from a maximum of 1.544 megabits per second (medium data rate) to 8 megabits per second (high data rate). Along with capacity, the new system will provide an almost tenfold increase in the number of spot beams for improved user access. These small beams will focus power to improve reliability and data rates to small and large terminals and to minimize interception and interference opportunities for regional adversaries. Overall, the AEHF System network will support twice as many tactical networks as Milstar. Improvements in network capability will also help ensure compatibility with international partners.

As in Milstar, the AEHF System crosslinks will enhance routing and reduce vulnerability to terrestrial disruption. The new crosslinks will operate at several times the current Milstar data rate.

By 2010, about 2500 terminals are expected in the protected communications inventory for the Air Force, Navy, Army, and Marines. Portable, mobile, and fixed terminals with low, medium, and high data rates will support ground units, aircraft, surface ships, and submarines. Standard antennas will range in size from a few centimeters to about 3 meters. Applicable milsatcom terminals include the Family of Advanced Beyond line-of-sight Terminals (FAB-T), the Single-Channel Antijam Man-Portable Terminal (SCAMP), Secure Mobile Antijam Reliable Tactical Terminal (SMART-T), and Submarine High Data Rate (Sub HDR) system. The FAB-T combines two previous programs, the Airborne Wideband Terminal and Command Post Terminal Replacement, and establishes a family of terminals with a common open architecture for airborne and ground applications.

For mission control, the system will have a dedicated segment consisting of communications management, mobile command and control centers, Satellite Ground Link Standard/Unified S-Band (SGLS/USB) satellite control, and EHF in-band satellite control. The CCS-C will interface with the AEHF satellite control to provide SGLS/USB command capabilities.

The Advanced Extremely High Frequency system will have as much as 12 times the total throughput of Milstar, in some scenarios. Single-user data rates will increase to 8 megabits per second. The system will also provide a large increase in the number of spot beams for improved user access. (Lockheed Martin Missiles and Space Systems)

Advanced Polar System

The demand for protected polar satellite communications to support submarines, aircraft, and other platforms and forces operating in the high northern latitudes has steadily increased over the last twenty years. In 1995, the Pentagon's Joint Requirements Oversight Council approved the Polar Operational Requirements Document, which paved the way for a program to address the polar communications demand. Subsequently, the decision was made to place a series of modified EHF payloads onto host satellites. The first package was launched in 1997, and the remaining two are scheduled for launch within the next three years. Although this hosted capability will provide a critical service to the end of this decade, it only meets a small fraction of the requirements spelled out in that 1995 Operational Requirements Document. Consequently, a replacement system is being considered for the 2008–2010 timeframe. The Air Force Space Command and the MILSATCOM Joint Program Office recently completed a polar concept study that covered 35 wide-ranging options for a future polar capability. As a result of this study, two satellites in highly inclined, highly elliptical molniya orbits have been recommended. In addition, transformational initiatives within the Department of Defense have put forward a proposed National Strategic SATCOM System that would combine worldwide and polar coverage for highly survivable communications, all in one system.

Narrowband Communications

In the past, the term "narrowband" implied data rates of less than 64 kilobits per second, but a higher boundary could apply in the future as higher data rates to small terminals become possible. Mobile and other small terminal users depend on high-power, low-data-rate satellite systems to receive data via broadcast (as in the Navy's Fleet Broadcast) and for two-way communications. Narrowband needs—generally transmitted in the ultrahigh-frequency (UHF) range—are supported by the UFO constellation, which will be replaced by a component of the Advanced Narrowband System.

Advanced Narrowband System

The Advanced Narrowband System is DOD's next-generation narrowband tactical satellite communications system, and its goal is to provide global narrowband communications services to tactical users (who are typically quite mobile). The Advanced Narrowband System consists of six segments: DOD space; commercial space; telemetry, tracking, and command; network control; user entry; and gateway.

The Mobile User Objective System is the successor to the Navy's current Boeing-built UFO system and is the key transport element in the Advanced Narrowband System. The Mobile User Objective System will provide beyond-line-of-sight communication to support mission objectives across all branches of the military.

The Communications Satellite Program Office of the Space and Naval Warfare Systems Command has completed concept studies resulting in several approaches to addressing narrowband needs. Aerospace has supported the Navy in evaluating these approaches and has collaborated, from an Advanced Narrowband System perspective, on possible commercial satellite communications augmentation aspects.

The Ground Multiband Terminal is a tactical satellite communications ground terminal that will support operations in the X, C, Ku, and military Ka bands. (Harris Corporation)

The current UFO constellation has eight satellites, plus one on-orbit spare, each of which provides a mix of 38 UHF communication channels at 5 and 25 kilohertz and one 25-kilohertz fleet broadcast channel. About 7500 UHF terminals are in use today. The capacity of this system will fall far short of anticipated needs by the end of this decade, considering that the estimated 2010 Combined Major Theaters of War requirement is about 42 megabits per second with over 2,300 simultaneous accesses—hence, the urgent need for the Advanced Narrowband and Mobile User Objective Systems. Launches could begin before the end of the decade, paving the way for full operational capability by 2013. The number of narrowband satellite communications terminals of all types is expected to approach 82,000 in 2010. About 50 percent of those will be handheld Combat Survivor Evader Locator units, and the remainder will be predominately legacy and advanced Joint Tactical Radio System terminals.

The Mobile User Objective System will employ commercial technology to enable communications with users of large terminals and small or handheld terminals. Commercial systems such as Thuraya in the Middle East and AceS in Southeast Asia have shown that more than 10,000 low-data-rate handheld terminals can be serviced over a region with one satellite. Large multibeam antennas, some more than 12 meters in diameter, enable the use of several hundred spot beams to improve signal-to-noise levels and achieve up to 30 times frequency reuse. Systems with these capabilities currently operate at L-band (1.5 gigahertz downlink) frequencies.

In addition to the Mobile User Objective System, the Navy is keeping other alternatives open for meeting Advanced Narrowband System requirements. One alternative would be to field or lease commercial systems, if the commercial market proves sufficiently mature. Another option would be to field additional evolved UFO satellites to allow the commercial sector to mature and improve government options. The Navy has dubbed this alternative "UFO-E," indicating that the Navy would consider continuing the UFO constellation with gradual improvements.

Accelerating Capability

In early fiscal year 2002, DOD initiated a Transformational Communications Study to accelerate the delivery of advanced capabilities with state-of-the art technology to the field. The study is led by the National Security Space Architect (NSSA) and is springboarding off the NSSA's Mission Information Management Communications Architecture (see sidebar, The Space Architect). The study is examining increased intersystem connectivity via optical crosslinks, greater reliance on ground fiber where possible, and the use of commercial assets as appropriate. Potentially, all U.S. government satellite communications programs in planning or development could be affected.

The Space Architect's vision of the future closely integrates government satellite communications into a system of systems. Additionally, it treats communications as an enterprise and balances air, space, and ground communications capabilities.

A large part of achieving advanced capabilities involves applying the best technology to emerging programs. To ensure milsatcom's technological edge in world satellite communications, the MILSATCOM Joint Program Office has established a Milsatcom Innovation Center to accelerate the insertion of emerging technologies into new systems. Aerospace, MITRE, MIT Lincoln Laboratory, and NASA's Jet Propulsion Laboratory are contributing onsite to the Center's activities. Milsatcom will most definitely have a new look in the future.