Satellites provide many significant services, including communication, navigation, remote sensing, imaging, and weather and meteorological support. Satellites support direct radio communication and provide television broadcast and cable relay services, as well as home reception. Satellite services also support applications such as mobile and cellular communication, telemedicine, cargo tracking, point-of-sale transactions, and Internet access. Satellites also provide redundancy and backup capabilities to ground-based communications, as was demonstrated after the events of September 11, 2001, when satellites provided critical communications while ground-based lines were unavailable. The commercial satellite industry includes manufacturers, the launch industry, service providers, and ground equipment manufacturers. Manufacturers design and build satellites, supporting systems, and ground stations. The launch industry uses launch vehicles, powered by rocket engines, to place satellites in orbit. Once commercial satellites are in orbit, they are operated by service providers, who lease available services. Commercial satellite service clients include telecommunication companies, television networks, financial institutions, major retailers, Internet service providers, and governments. Some companies resell leased satellite services to their clients. For example, major telecommunication companies sometimes include satellite services in their product line. Ground equipment manufacturers build and sell the items needed to use satellite services, such as ground station hardware (antennas), data terminals, mobile terminals (truck-mounted units), and consumer electronics (satellite phones). For the year 2000, the commercial satellite industry generated revenues of $85.1 billion: $17.2 billion for satellite manufacturing, $8.5 billion for the launch industry, $41.7 billion for satellite services, and $17.7 billion for ground equipment manufacturing, according to an industry association. Federal agencies also own and operate satellites. For example, the U.S. military and intelligence communities have satellites to provide capabilities for reconnaissance, surveillance, early warning of missile launches, weather forecasts, navigation, and communications. In addition, some federal civilian agencies own satellites that are used for communications, scientific studies, and weather forecasting. Further, federal agencies use commercial satellites for services such as communications, data transmission, and remote sensing. For example, DOD typically relies on commercial satellites to fulfill its communications and information transmission requirements for non–mission-critical data and to augment its military satellite capabilities. The National Defense Industrial Association (NDIA) reported in December 1998 that the government’s overall use of commercial satellites for communications and remote sensing is expected to grow significantly because of increased communications requirements. According to a DOD official, the department’s reliance on commercial satellites is expected to grow through 2020. After 2020, DOD officials anticipate that commercial satellites will provide only surge capacity, as additional military satellites are expected to be operational. In addition to the U.S. military, several civilian government agencies also rely on commercial satellite systems. Table 1 provides brief descriptions of the use of commercial satellites by four civilian agencies included in our review. Collectively, the federal government does not dominate the commercial satellite market. According to commercial satellite industry officials, the revenue provided to the satellite industry by the federal government represents about 10 percent of the commercial satellite market. However, the importance of commercial satellites for government operations is evident during times of conflict. For example, according to a DOD study, commercial communications satellites were used in 45 percent of all communications between the United States and the Persian Gulf region during Desert Shield/Desert Storm. Further, during operations in Somalia from December 1992 through March 1994, U.S. military and commercial satellite coverage was not available, so Russian commercial satellites were used. DOD currently reports approximately 50 percent reliance on commercial satellites for wideband services, which are leased through the Defense Information Systems Agency’s Commercial Satellite Communications Branch. The commercial satellite industry is a global industry that includes many foreign-owned corporations as well as partnerships between U.S. and foreign corporations. As a result, the U.S. government depends on foreign and international companies. For example, some commercial space systems of foreign origin are used by the U.S. military for imagery and communications support. NDIA reported that foreign ownership of satellites is expected to grow and predicted that by 2010, 80 percent of commercial communication satellite services could be provided by foreign- owned companies. This globalization of the satellite industry could affect the availability of commercial satellite systems to U.S. government or commercial entities through frequency allocations, tariffs, politics, and international law. A satellite system consists of ground stations, tracking and control links (commonly referred to as the tracking, telemetry, and control (TT&C) links) and data links, and satellites. Figure 1 illustrates the basic satellite system components. As the figure shows, two kinds of ground stations are associated with satellites: control stations and communications stations. Control stations perform tracking and control functions to ensure that satellites remain in the proper orbits (commonly referred to by the industry as “station keeping”) and to monitor their performance. Communications ground stations process imagery, voice, or other data and provide, in many cases, a link to ground-based terrestrial network interconnections. The links between the two types of ground stations and the satellites are referred to by their function: TT&C and data links. TT&C links exchange commands and status information between control ground stations and satellites. Data links exchange communications, navigation, and imaging data between communications ground stations and satellites. As shown in figure 1, links are also distinguished by the direction of transmission: uplinks go from Earth to space, and downlinks from space to Earth. Satellites can also communicate with each other; these links are referred to as cross-links. The final component of the system is the satellite. Every satellite has a “payload” and a “bus.” The payload contains all the equipment a satellite needs to perform its function, and it differs for every type of satellite. For example, the payload for a weather satellite includes cameras to take pictures of cloud formations, while the payload for a communications satellite includes transponders to relay data (for example, television or telephone signals). The bus carries the payload and additional equipment into space and provides electrical power, computers, and propulsion to the entire spacecraft. A satellite can serve simply as a relay between a source and a destination (for example, a communications satellite), or it can perform processing of data and communicate the data to a communications ground station (for example, an imaging satellite). Satellite systems face unintentional threats to all parts of the system; such threats can be ground-based, space-based, and interference-oriented. The probability of these threats occurring and the difficulty of exploiting these vulnerabilities vary. Table 2 displays some of these threats and the vulnerable components. Ground stations are vulnerable to damage or destruction by natural terrestrial threats such as earthquakes, floods, thunderstorms, lightning, dust storms, heavy snows, tropical storms, tornadoes, corrosive sea spray, and salt air. In addition, they could also be affected by natural conditions and environmental hazards, such as air pollution and adverse temperature environments, as well as power outages. Satellites are physically vulnerable to space-based environmental anomalies resulting from natural conditions and man-made artifacts. Space-based threats include solar and cosmic radiation and related phenomena, solar disturbances, temperature variations, and natural objects (meteoroids and asteroids). In addition, the growing number of satellites is contributing to the problem of space “junk” (spacecraft and debris). As of May 2002, DOD identified over 9,000 man-made objects in space, including active satellites. As additional satellites are developed and deployed, DOD officials stated that the threat of collisions caused by the proliferation of satellites and accompanying debris could increase. Links are vulnerable both to natural conditions (in space and in the atmosphere) and to congestion. Links can be severely degraded by the effects of solar activity and atmospheric and solar disturbances. Both orbital and spectral congestion are a threat to links (as well as to satellites). Such congestion may restrict the future use of potential orbits and frequencies and cause unintentional interference to satellite services. According to one commercial service provider, satellite service providers worldwide work together to resolve interference problems, which are common. In addition, commercial satellite interference is regulated both internationally and nationally. The International Telecommunication Union specifies interference resolution policies and procedures, including those for harmful interference. Further, within the United States, the Federal Communications Commission (FCC) has the capability to track the location of interference, at a service provider’s request. Also, service providers told us that they could locate and identify unintentional or unauthorized users through a technique called triangulation. Once an unauthorized user is located, a commercial service provider can jam that user’s signal if the user cannot be persuaded to stop using the satellite. However, according to industry officials, typically an unauthorized user would be identified, located, and contacted through a combination of industry and government resources before such jamming would be needed. In addition, satellite systems are vulnerable to many forms of intentional human attacks that are intended to destroy ground stations and satellites or interfere with the TT&C links, data links, and cross-links. According to DOD and the private sector, the probability of these threats occurring and the difficulty of exploiting these vulnerabilities vary. Table 3 shows some of these intentional threats. All types of ground stations are potentially vulnerable to threats of physical attack and sabotage. These threats could target all satellite ground components, including launch facilities, command and control facilities, and supporting infrastructures. Space-based threats to satellites are proliferating as a result of the growing availability of technology around the world. According to DOD, potential space-based weapons include interceptors, such as space mines and orbiting space-to-space missiles, and directed-energy weapons.