Suchergebnisse

A letter report issued by the General Accounting Office with an abstract that begins "In recent years, the Department of Defense (DOD) has come to rely more heavily on commercial satellite communications to plan and support operations and move toward a network-centric warfare environment. DOD acquires commercial satellite bandwidth services to support a variety of critical missions such as surveillance performed by unmanned aerial vehicles. GAO was asked to assess (1) whether DOD's process for acquiring these services is fair to vendors and providers, (2) whether the process meets users' needs, and (3) whether spending on these services is managed effectively and efficiently."

The U.S. military's increasing reliance on commercial and military communications satellites to enable widely-dispersed, mobile forces to communicate makes these space assets increasingly vulnerable to attack by adversaries. Attacks on these satellites could cause military communications to become unavailable at critical moments during a conflict. This research dissected a typical satellite communications system in order to provide an understanding of the possible attacker entry points into the system, to determine the vulnerabilities associated with each of these access points, and to analyze the possible impacts of these vulnerabilities to U.S. military operations. By understanding these vulnerabilities of U.S. communications satellite systems, methods can be developed to mitigate these threats and protect future systems. This research concluded that the satellite antenna is the most vulnerable component of the satellite communications system's space segment. The antenna makes the satellite vulnerable to intentional attacks such as: RF jamming, spoofing, meaconing, and deliberate physical attack. The most vulnerable Earth segment component was found to be the Earth station network, which incorporates both Earth station and NOC vulnerabilities. Earth segment vulnerabilities include RF jamming, deliberate physical attack, and Internet connection vulnerabilities. The most vulnerable user segment components were found to be the SSPs and PoPs. SSPs are subject to the vulnerabilities of the services offered, the vulnerabilities of Internet connectivity, and the vulnerabilities associated with operating the VSAT central hub. PoPs are susceptible to the vulnerabilities of the PoP routers, the vulnerabilities of Internet and Intranet connectivity, and the vulnerabilities associated with cellular network access.

Other written product issued by the General Accounting Office with an abstract that begins "Pursuant to a legislative requirement, GAO reviewed the Federal Communications Commission (FCC) new rule on direct broadcast satellite public interest obligations. GAO noted that: (1) the rule would impose requirements on direct broadcast satellite service (DBS) providers to comply with the political broadcast rules of the Communications Act of 1934, as amended, and mandates that the DBS providers reserve between 4 percent and 7 percent of their channel capacity exclusively for noncommercial programming of an educational or informational nature; and (2) FCC complied with applicable requirements in promulgating the rule."

(1). Sen Dan: Development policies, plans and programmes of satellite communications in China. - 6 S.; (2). Gao Fuwen ; Li Weiwei ; Li Danian: PC-based audio/graphics/video image satellite communication education system and its applications. / Beijing Normal University. - 9 S.; (3). Xing Chunjie: Satellite tv education in China. - 5 S.; (4). Zhang Zhijian ; Ren Xianglin: The development of radio and television broadcasting service and satellite broadcasting in China. / The Ministry of Radio, Film and TV. - 4 S.; (5). Ma Junru: Satellite communications in China. Review and outlook. - 6 S.; (6). Hao Weimin: The application of satellite communications system in rural areas. - 2 S

This dissertation describes a novel method of providing position-location from geosynchronous communication satellites. The Global Positioning System (GPS) has become the standard for position-location and navigation in the world. It provides extremely accurate coordinates to military users and slightly less accurate coordinates to "non-authorized" users. Disadvantages of GPS are complexity and high cost. The U.S. Department of Defense (DoD) has spent billions of dollars in developing and fielding the system. Maintenance and GPS satellite replenishment costs will continue to climb. A simpler, lower cost alternative to the GPS system is explored. This study describes a position-location system using transponders on-board geosynchronous communication satellites. The system uses three geosynchronous communication satellites at a time to relay synchronized television signals. The signals provide a timing system to measure the ranges from the satellites to the receiver. The least squares method is used to calculate the location of the receiver. A software model is developed to demonstrate the ability of the system to "track" three geosynchronous satellites and calculate receiver position. A test is conducted to demonstrate the use of television signals to provide timing for the system. The basic model is further refined by adding perturbation forces which act on the satellites. The Intelsat Eleven-Parameter algorithm is incorporated into the systenl model and provided the most precise location of the satellites. The accuracy of the proposed system in determining the position-location of the receiver is estimated based on the results of the simulation and the test. Further research is proposed to build on the concepts discussed in this dissertation. ; Ph. D.