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GPS APPLICATIONS AND REQUIREMENTS 20 Although the continued existence of GPS as a dual-use system clearly requires some trade-offs between civilian utility and national security, the NRC committee has concluded from its deliberations that because GPS provides tremendous benefits to both civilian and military users, as the remainder of this chapter will clearly illustrate, it should firmly remain a dual-use system. From the committee's perspective, recognition that GPS is truly a dual-use system brings with it the responsibility of meeting the requirements of all users to the highest degree possible. This implies that the system must be designed to the specifications of both civilian and military requirements. Many nonmilitary users of GPS have requirements that have been validated by standard-setting bodies and federal agencies that can now only be achieved through the additional cost of differential GPS (DGPS). Because human safety is an important consideration for many of these applications, a specified level of accuracy is not the only requirement. Integrity, availability, and resistance to RF (radio frequency) interference (both intentional and unintentional), as defined in Appendix C, are of significant importance as well. The sections that immediately follow discuss these requirements for each user category. The task given to the NRC committee by Congress also recognized the dual-use nature of GPS and the trade-offs that exist between civil and military utility when it asked the following questions: "What augmentations and technical improvements to the GPS itself are feasible and could enhance military, civilian, and commercial use of the system?"; and, "What are the implications of security-related safeguards and countermeasures for the various classes of civilian GPS users?" These questions are examined in the remainder of the chapter by determining the challenges that currently exist for full utilization of GPS in each user community, including challenges that are related to Selective Availability (SA) and Anti-Spoofing (A-S). Although some of these challenges relate to the limitations of associated technologies and technology policies, findings in this chapter reveal that the biggest challenge for most users is meeting the requirements of a given application through augmentation of the GPS SPS. It stands to reason, therefore, that improving the basic capabilities of GPS and the freely available SPS signal will enhance the ability of civilian users to meet their requirements more easily, more cost-effectively, and in some cases, without augmentation or enhancement from DGPS or other positioning technologies. Improvements to the basic GPS can be made that will improve the military's ability to meet its requirements as well. Specific technical recommendations that would achieve this goal and address the tasks assigned to the NRC committee are discussed in detail in the next chapter. GPS MILITARY APPLICATIONS Although the overall use of GPS in the civilian sector has grown much faster than military usage, the system was designed with military requirements in mind, and the importance of the system to national security has not diminished. GPS is more accurate than any other radionavigation or positioning technology developed by the DOD, and is beginning