The Global Positioning System: A Shared National Asset (1995)
Chapter: SUMMARY
Findings
The presence of SA has little or no effect on the ability to use GPS for orbit determination, but A-S limits the performance of orbit determination for spacecraft that rely on dual-frequency measurements, such as Topex/Poseidon.
SA has no effect on the accuracy of GPS attitude determination methods for spacecraft. A-S may place some limitations on achievable accuracy, but so do design parameters related to receiver electronics and antenna structure.
The ability to use GPS for orbit determination on board geosynchronous satellites will be lost if the Block IIR and IIF spacecraft are built with narrower beamwidth antennas than the Block II/IIA satellites.
Summary
Although this chapter does not represent a complete list of all GPS applications and their requirements, it should be clear from its content that the Global Positioning System has become an integral part of our nation's technical infrastructure, which contributes to our security, economy, and overall quality of life. Indeed, a fully exhaustive list of GPS applications may be impossible to compile, for as soon as it was completed, dozens of new and innovative applications, such as navigation systems for the visually impaired, would be developed that exploit GPS to the limits of its technological capability. Although requirements for currently undiscovered applications such as this one cannot be quantified, a strong case can be made for not only maintaining the basic system's operational capability but also for continuously improving it in order to meet the increasingly demanding requirements of a multitude of military and civilian users who rely on GPS on a routine basis.
The tables included in this summary represent a compilation of the GPS applications that have been discussed in this chapter. Military applications with accuracy requirements currently unmet by the PPS are included in Table 2-11, and civil applications are grouped according to their accuracy requirements in tables 2-12 though 2-16. As these tables and the preceding discussions in this chapter clearly illustrate, the civilian applications that currently require augmentation or enhancement of the GPS SPS far outweigh those that do not. Most integrity and availability requirements for civilian applications are also unmet by the GPS SPS and are highlighted in the tables through the use of grey shading. Candidate technical improvements and modifications to the basic GPS that would enhance its functionality and make it more capable of meeting the requirements of both civilian and military users are discussed in the next two chapters.
Table 2-11 Summary of Military Applications with Accuracy Requirements Unmet by the GPS PPS as Currently Specifieda
Table 2-12 Summary of Civilian Applications with Accuracy Requirements of 100 Meters or Greater (currently achievable with the basic GPS SPS)a
Table 2-13 Summary of Civilian Accuracy Requirements Between 25 and 100 Metersa
Table 2-14 Summary of Civilian Accuracy Requirements Between 10 and 25 Metersa
Table 2-15 Summary of Civilian Accuracy Requirements Between 1 and 10 Metersa
Table 2—16 Summary of Submeter Civilian Accuracy Requirementsa
