Military Satellite Communications: Then and Now
Military Satellite Communications: Then and Now
Military satellite communications have become essential to help the warfighter see through the “fog of war,” providing the United States military with assured global connectivity, even in remote areas with no communications infrastructure. The Aerospace Corporation has played a key role in developing and fielding these vital space systems.
Mak King and Michael J. Riccio
Long before the first man-made satellites reached orbit, late nineteenth- and early twentieth-century scientists and visionaries understood the potential for space-based communications and developed orbital parameters. Then, in 1946, the U.S. Army bounced radar signals off the moon. This experiment was followed in the 1950s and 1960s by U.S. Navy moon-bounced communications. In October 1957, the Soviet Union surprised the world by launching the first artificial satellite. For a few days, the beeping Sputnik—23 inches in diameter and 183 pounds in weight—circled Earth every 96 minutes. A year later, on December 18, 1958, the U.S. Air Force Ballistic Missile Division, predecessor of the Air Force Space and Missile Systems Center (SMC), launched the U.S. Army’s Signal Communication by Orbiting Relay Equipment (SCORE) into a 101-minute orbit. The 150-pound payload of modified commercial equipment built into an Atlas missile fairing stored uploaded data on tape to be later transmitted to ground receivers. Before its batteries ran down on December 31, SCORE made President Eisenhower’s 56-word Christmas wish “for peace on Earth and goodwill toward men everywhere” the first voice message transmitted from space.
Courier, the next communications satellite launched by the Department of Defense (DOD), had store-and-rebroadcast capability. It was the world’s first active repeater satellite and featured solar cells that would recharge its batteries.
Passive reflector demonstrations followed. A 100-foot aluminized plastic balloon named Echo was launched in 1960. In 1963, millions of tiny wires, each about the size of an eyelash, were sent into orbit to reflect signals. Within a few months, the wires had dispersed too widely to reflect a useful signal, and no more “needle” experiments were attempted. One early communications pioneer, scaling from the first trans-Atlantic telephone cable, which carried 36 telephone calls at a cost of approximately $40 million, estimated a satellite’s capacity at 1000 calls, and wondered if a satellite could be worth a billion dollars.
Commercial entities quickly realized the potential of satellites, and military and commercial developers alike learned from each other as space technology progressed. A private, multinational consortium paid NASA to launch the Telstar satellite in July 1962. Syncom 3, the first satellite in geosynchronous orbit (GEO), was launched in August 1964; it relayed television coverage to the United States from the Tokyo Summer Olympics. Global satellite communications had begun and were enabling other space system capabilities as well, such as weather forecasting and navigation.
In 1962, the Air Force asked Aerospace to provide support in the emerging discipline of systems engineering to what was then called the Initial Defense Communication Satellite Program (IDCSP). First launches occurred in 1966, and eventually, 26 IDCSP satellites were distributed in drifting orbits around the world. The 100-pound satellites each had a single repeater but no batteries and no position or attitude control. When the system was declared operational in 1968, its name was changed to the Defense Satellite Communication System (DSCS). Aerospace continued to support the design, development, deployment, and operation of this system’s space and ground elements—the latter being comprised of two large fixed and 34 transportable terminals.
Aerospace testimony affected a 1964 congressional decision that U.S. military satellite communications systems should be developed separately from commercial systems because of the military’s unique and vital national security requirements. The military has always used commercial satellites and services where appropriate, however.
Over the years, increasing demand for capacity has required improved satellite designs. For example, closing links to tactical users with small terminals required more radio transmitter power, which in turn required more satellite power, more efficient solar cells, and eventually, a new stabilization technique with attitude control and station-keeping capabilities to allow capture of more of the sun’s energy. During this time, it was also becoming necessary to have ground control of satellite position and orientation, and these evolving needs led to larger satellites. Aerospace played a key role in concept development, proof, and refinement of these techniques, which are now fundamental to all military satellite communications (see sidebar, Military Satellite Communications Fundamentals).
The Range of Systems
By the early 1970s, the DOD realized that military satellite communications needed an architecture—that is, a technology and program development plan to ensure warfighters’ requirements were efficiently met. The predecessor of what is now the Defense Information Systems Agency (DISA) was assigned this task; the office was headed by an Aerospace engineer on loan from the corporation. Support from Aerospace and the entire military satellite communications community resulted in the first comprehensive architecture for these satellite systems. Documents published in 1976 described this architecture, which grouped users with similar requirements into three types of systems: wideband, narrowband/mobile (or tactical), and protected (for nuclear-capable forces). Today, Aerospace personnel in Virginia continue to support DISA’s ongoing architectural efforts. In addition, Aerospace’s risk and performance evaluations have been pivotal in the architectural decisions preceding every major military satellite communications acquisition(see sidebar, Aerospace’s Role in Military Satellite Communications Acquisition).
Wideband Services and Systems
In 1968, DOD asked Aerospace to assist with DSCS Phase II, which had multiple channels for higher communications capacity and enhanced position and orientation control. The first pair of Phase II satellites were launched in late 1971. Soon, mission requirements began to change dramatically, with increased demand for smaller, transportable, or mobile terminals along with point-to-point or networked connectivity and coverage ranging from in-theater to global. These increased demands gave rise to the next generation, DSCS III. These satellites had the flexibility to connect channels to eight antennas, including antennas that formed multiple beams whose size, shape, and location were determined by ground command. The first DSCS III was launched in 1989 (the last DSCS II was also launched on the same rocket); it was followed by 11 more DSCS III satellites—all of which are operational today. The last four were upgraded by means of the Service Life Enhancement Program (SLEP), which increased overall communications capacity by 200 percent and increased capacity to tactical users by up to 700 percent. Aerospace fulfilled key acquisition roles in both DSCS III and SLEP.
Also serving wideband users is the Global Broadcast Service (GBS). This service is provided by payloads hosted on satellites from other systems. GBS delivers one-way, high-speed data to tactical forces with small, portable terminals. Aerospace investigated the applicability of commercial waveforms and equipment and wrote the initial GBS specifications for both payloads and terminals.
Today’s reigning king of the wideband systems is the Wideband Global Satcom (WGS) program. Started in 2000 as the Wideband Gapfiller Satellite, it was renamed when budget constraints indefinitely delayed the future Advanced Wideband System. An acquisition partnership with Australia has increased the number of WGS satellites and support to the Southwest Pacific region. Each WGS satellite supports two-way tactical and one-way GBS communications and provides more capacity than the entire DSCS constellation.
The WGS payload continues services in the X band (similar to DSCS) and expands services into the military Ka band. Service in both bands is enhanced by sampling and digitizing channel inputs, which enables modern digital filtering and flexibility in switching signals between uplink and downlink beams. In addition to Earth coverage, X-band service employs new uplink and downlink phased-array antennas, which shape beams to optimize coverage in that band. Service at Ka band is through high-gain gimbaled dish antennas, which enable high-data-rate service to relatively small, disadvantaged terminals. The digitizing payload also allows cross-banding between the X and Ka bands, further enhancing flexibility. Aerospace was intimately involved in all phases of the WGS program, from early concept definition to acquisition, development, and fielding.
Mobile and Tactical Systems
Mobile and tactical military satellite communication systems are characterized by terminals with small antennas on ships, submarines, boats, land vehicles, and aircraft. They also service large transportable terminals, lightweight backpack terminals, and even handheld terminals or terminals located on cruise missiles. They primarily convey voice and data (with growing applications to include telemetry, imagery, texting, file transfer, remote sensor computer access, paging, email and Internet, and facsimile) and extend to video teleconferencing and video.
One such tactical system is the Navy’s Fleet Satellite Communications (FLTSATCOM) system, the DOD’s first operational satellite communications system dedicated to tactical users. Aerospace assisted the Air Force in acquiring and launching this primarily UHF system. Another tactical system, Leasat, was directed by Congress in 1976 to be a leased commercial service. Leasat had launches from 1984 to 1990, which extended UHF service into 1996. By 1991, the Navy was operating six FLTSATCOMs and four Leasats; all were deactivated by 1999 to save sustainment costs.
The UHF Follow-On (UFO) system continued UHF communications and added a small EHF payload beginning on Flight 4 that had multiple channels configurable between an Earth-coverage antenna and a narrow-beam steerable spot antenna. Beginning with UFO-7, capacity of this EHF payload was doubled and a GBS Ka-band package was added. Ten UFO satellites launched between 1993 and 2003 remain in use. Aerospace supported the Navy throughout UFO’s development and deployment, performing mission assurance, analyzing communications, and developing a telemetry analysis workstation for a satellite control center.
The future successor to UFO will be the Navy’s Mobile User Objective System (MUOS), a narrowband system with enhanced access, capacity, quality, and communications-on-the-move for a wide range of DOD and government mobile users. MUOS data rates range from 75 bits per second to 64 kilobits per second in broadcast, point-to-point, and full duplex network topologies. Aerospace supported the Navy with link and Internet Protocol (IP) communications analysis, traffic models, and other requirements analysis, as well as with other mission assurance roles.
The United Kingdom’s Skynet series (first launched in November 1969) and the NATO satellites (first launched in March 1970) are compatible with each other and with U.S. system waveforms. The Air Force and Aerospace led efforts to promote allied interoperability through development of international waveform standards and participated in numerous interoperability demonstrations and tests.
The need to operate in contested environments (for example, a battlefield or area where signals are being intentionally jammed) characterizes protected users of the military satellite communications architecture. These users accept low to moderate data rates in exchange for protection against detection, interception, jamming, spoofing, and scintillation, as well as effects from nuclear detonations.
The Air Force Satellite Communications System (AFSATCOM) was one such protected system. Designed in the mid-1960s, these payloads were hosted on several satellite systems, including FLTSATCOM and DSCS. Early North-polar region coverage was provided with payloads hosted on satellites in high-inclination orbits. Channels at X band and UHF provided some uplink jamming protection using frequency-hopping. An AFSATCOM payload hosted on Milstar (the current highly protected military satellite communications system) provides continuing AFSATCOM connectivity, although most other AFSATCOM payloads have been removed from service. Aerospace provided substantial performance analysis and participated in development, fielding, and operational testing.
Milstar was initially contracted in March 1982 after several years of successful terminal and space risk-reduction contracts. It can operate independent of ground control, relay stations, and distribution networks because of its advanced onboard processing and satellite-to-satellite crosslinks. Milstar’s system design emphasized robustness in communication, even in the presence of adverse conditions such as jamming or nuclear attack, and has the flexibility to provide worldwide unscheduled connectivity to a wide range of terminal/platform combinations under changing or uncertain link conditions.
Milstar has three segments: mission control, terminal, and space. The mission control segment plans Milstar’s missions, assesses system resource allocation, and tests and controls the satellites from fixed and transportable facilities. Crosslinks enable monitoring and control of all Milstar satellites from a single location. The terminal segment includes many types of terminals developed separately by the Air Force, Navy, and Army; antenna diameters vary from 14 centimeters to 3 meters.
The space segment comprises the satellites, first launched in February 1994. The first two satellites (Block I) carried a low-data-rate (LDR) payload, providing warfighters robust connectivity. By 1997, Milstar was declared operational. Even before initial launches, a program restructure in response to global political changes that included the end of the Cold War and the start of the Gulf War created Block II, with both LDR and a more tactically oriented medium-data-rate (MDR) payload. Aerospace was instrumental in the development of the LDR and MDR waveform standards as well as Milstar architecture and system design.
Milstar Block II continues most of Block I’s robust features such as operation in the EHF band (wide bandwidth and high-gain, narrow-beam antennas), frequency-hopping, onboard processing, crosslinks, and crossbanding to UHF. Features that support flexibility include onboard processing that enables user-defined connectivity, including data rate, uplink and downlink signaling modes, beam selection, and routing of individual signals. The Milstar constellation is, in effect, a “switchboard in the sky” because of the flexible connectivity it provides. The Block II satellites were launched in February 2001, January 2002, and April 2003. All five remain in service.
The successor to Milstar is the Advanced EHF (AEHF) system. Aerospace played a central acquisition role in its definition and development, ensuring AEHF compatibility with Milstar terminals and control elements, continuing and extending strategic and tactical protected communication services, and reducing bandwidth restrictions for the warfighter. AEHF satellites sustain many Milstar features for continued flexibility and robustness, but also include an extended data rate (XDR) waveform and more channels, which substantially expand capacity. The system will provide an order-of-magnitude increase in communications capacity relative to Milstar while maintaining protective features. Advanced antenna technology will provide many more beams, improve worldwide coverage, and increase connectivity to small terminals that can rapidly set up and establish communications to follow a fast-moving battle front.
Three AEHF satellites and a mission control segment are being developed, with additional satellites now being programmed. One unique AEHF feature is that three allies are important international partners in the program. The United Kingdom, Canada, and the Netherlands have participated financially and programmatically in AEHF system development and will benefit by having dedicated AEHF resources, constellation-wide, allocated for their national use. Aerospace had a key role in the technical and programmatic discussions that led to these agreements, and continues to fulfill an important acquisition role in the development and fielding of the AEHF program.
Aerospace played a crucial role in government studies that concluded in 2002 with a call for the development of a new architecture. The centerpiece of this new architecture would have been the Transformational Communications Satellite (TSAT). It would have had an advanced onboard payload for the space layer of the Global Information Grid and a space-based laser communications backbone. Links from airborne intelligence, surveillance, reconnaissance platforms via Ka band and laser would reach 2.5 Gb/sec. Use of an XDR and a new XDR+ waveform would increase individual EHF user data rates to 45 megabytes per second and provide communications-on-the-move to small, mobile users. The TSAT mission operations system would manage TSAT and AEHF.
Aerospace played a crucial role in risk reduction, requirements development, and the initial acquisition phases of the TSAT program; however, although TSAT requirements remain valid, the program was cancelled in 2009 as part of a larger restructuring of DOD acquisition priorities.
Aerospace is currently studying capability insertion programs and evolutionary enhancements to future AEHF and WGS satellites with an emphasis on “harvesting” TSAT technology development and risk reduction and improving capability at a small cost in the near term—for example, through the use of advanced antennas and processing. Other concepts under consideration include using commercial satellites for rapid capability demonstrations taking five years or less from conception to launch.
Another example of Aerospace’s military satellite communications role is ensuring secure, critical communications in the North polar region, above 65 degrees N latitude. This is an essential adjunct to protected midlatitude military satellite communications. One approach is to host payloads on satellites in a highly inclined orbit with connectivity to midlatitude systems provided through ground gateways. Polar AFSATCOM payloads flown on several hosts beginning in the 1970s provided polar service until 2007.
In the late 1980s, Aerospace participated in an extensive analysis of alternatives for a polar adjunct program. More than 50 options were explored, including different orbits, varying hosts, unmanned aerial vehicles, new technologies, and even connecting via the telecom services of northern nations. In November 1993, the DOD decided on small EHF packages on host satellites. The first Interim Polar System (IPS) payload was launched in 1997, with second and third payloads launched in 2007 and 2008 to achieve 24-hour coverage. IPS now serves as the polar adjunct to Milstar.
In 2002, Advanced Polar Satellite (APS) studies began to examine how to extend protected military satellite communications capabilities into the polar region after IPS while minimizing new developments and modifications to existing terminals. Aerospace had drafted the APS requirements for the DOD by 2003. Then, the APS study team was directed to minimize the polar requirements under consideration. The primary trade was still between the traditional hosted payload versus a separate satellite. After studying 14 options, an Aerospace team was directed in 2005 to develop Enhanced Polar System (EPS) requirements. In December 2006, the DOD determined that the Air Force would be fully funded for the design, development, integration, and testing of EPS payloads 1 and 2 and its mission control system as the polar adjunct to the AEHF system. EPS will be hosted on the same line of satellites as IPS. EPS acquisition and system engineering work continues.
Aerospace has helped U.S. military satellite communications capabilities dramatically improve and expand during the past five decades. Systems have evolved from SCORE’s single channel to today’s high-capacity, flexible resources, including WGS, MUOS, and AEHF for wideband, tactical, and strategic users. Higher power, wider bandwidth, improved waveforms for protected communications, and flexibility for mobile users have increased information transmission flexibility to a widening assortment of terminal types.
While early satellite communications systems had a life span of days or weeks, today’s systems have design lives extending to 14 years and beyond, with a typical mean mission duration of 10 years. This is necessary to justify system effort and cost of development and operations. And yes, to answer that early question, a satellite can certainly be worth a billion dollars. Though commercial communications often favor fiber, the military will always need assured, covert communications that do not rely on existing infrastructure.
Another change over time is that satellite communication terminals have become smaller and more numerous. These terminals have evolved from a few large fixed terminals to thousands of small mobile terminals. Satellites have also become bigger, from early 100-pound satellites to 10-ton structures with solar panels spanning several hundred feet. Satellites have also become more capable, having ranged over the years from simple state machines to computers with millions of lines of code. In other ways, the acquisition process has come full circle, evolving from a time when commercial consortiums paid NASA to launch their early satellites to a time when NASA and DOD are now paying contractors for launches.
With 50 years of experience supporting the full range of military satellite systems, Aerospace is uniquely positioned to apply lessons learned from one space program to another. As military satellite communications systems evolve, mature, and give way to the next more-capable generation, Aerospace will continue to contribute in each phase of acquisition, development, and deployment.
The authors thank the MILSATCOM Division systems engineers and managers at Aerospace who are too numerous to mention—each lent their time to discussions and contributions on the programs described. The authors also thank Don Martin for his efforts and past publications, which serve as a valuable record of communication systems descriptions. Thanks also to the Aerospace corporate librarians, particularly Bonnie Smith, for their assistance.
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