Contents
Introduction
The direction of the NAVSTAR GPS system is guided by the results of studies which have been comissioned by various branches of the U.S. government. Persons who are interested in NAVSTAR GPS operations and management policy should obtain the studies listed below.DoT - DoD Dual Use Study
A study titled "The Global Positioning System: Management and Operation of a Dual Use System" was released in December 1993 by a joint task force composed of members of the U.S. Department of Defense and Department of Transportation. System management and funding mechanism options were reviewed based on civilian applications and accuracy requirements. The report may be viewed online at the U.S. Coast Guard Navigation Center. Recommendations of the study included:
- A joint DoD / DoT Executive Board should be established to resolve overall GPS policy and management issues.
- Basic GPS funding should continue to be financed though DoD appropriations from the general fund.
- Federal augmentations to GPS to support civil navigation functions should be financed through DoT appropriations from the general fund and indirect fees.
- DGPS services should be implemented for civil applications requiring greater accuracy better than that provided by GPS civilian or military service levels.
- A wide area broadcast DGPS service using communications satellites should be implemented to improve GPS availability and integrity for aviation users.
- Integrity information should be provided with all DGPS services
- Common government-wide GPS augmentation services should be implemented
- Private-sector DGPS services should not be used for navigation and should not be regulated.
- U.S. initiatives to promote international use of GPS should be continued.
- Ongoing DoD and DoT studies on the impacts of GPS jamming and spoofing should be continued.
NAPA and NRC
The National Academy of Public Administration (NAPA) and the National Research Council were requested by Congress to provide guidance on the future of GPS. Congress' intent was to determine how GPS should be managed, governed and funded in the future.The NAPA is a non-partisan, independent organization chartered by congress to give practical assistance to federal, state and local governments. The organization focuses on four dimensions of governance: public purposes, institutional roles and responsibilities, performance capacities and change. The NAPA study, titled "The Global Positioning System: Charting the Future" can be ordered directly from the NAPA, from the Navtech Bookstore or downloaded from the Coast Guard Navigation Center. Recommendations of the study were:
The National Research Council, a part of the National Academy of Sciences, advises the federal government on scientific issues. It provides services to the government, the public, and the scientific and engineering communities. The NRC study, titled "GPS: A Shared National Asset" is available online at the NRC web site, purchased from the NAS Bookstore or the Navtech Bookstore. Recommendations included in the report were:
- The President should adopt explicit national goals to guide future GPS policy making & implementation
- The US should commit to making GPS available to users free of direct user charges
- Because Selective Availability is not performing it's intended function, DoD should pursue other methods of denying use of GPS to potential adversaries.
- Selective Availability should be turned down immediately and deactivated after three years
- The US should broaden civilian participation in GPS governance.
Selective Availability
- Selective Availability should be turned to zero immediately and deactivated after three years. Prerogative to reactivate S/A to current levels should reside with the National Command Authority.
Anti-Spoofing
- Anti-Spoofing should remain on and electronic distribution of keys to authorized military users should be implemented at earliest possible date. Air Force shoud explore the necessity of upgrading current encryption method. Required receiver enhancements should be incorporated in future upgrades.
Technical Enhancements for Military Users
- Development of GPS receivers capable of direct acquisition of the encrypted Y code should be completed asap. Deployment of such receivers should be given high DoD priority. This is necessary because most receivers can't acquire the military GPS signals without first tracking the civilian signal, which would be jammed under wartime conditions.
- Anti-jamming antennas and antenna electronics should be employed wherever feasible and cost effective.
- Development of low-cost, solid-state, tightly coupled inertial navigation systems / GPS receivers should be accellerated in order to provide better anti-jam performance.
- Development of GPS receivers with improved jamming-resistance should be accellerated.
- Military receivers should be developed that can compensate for ionospheric errors when L1 (the civilian signal) is jammed, by improved software modelling and through local-area ionospheric corrections.
Performance Enhancements for Civil & Commercial Users
- Immediate steps should be taken to obtain authorization to use an L-band frequency for an additional civilian GPS signal and the new signal should be added to the GPS block II-R satellites at the earliest opportunity.
Performance Enhancements for All Users
- DoD's more frequent satellite navigation correction update strategy should be fully implemented as soon as possible following tests of it's effectiveness. Also, the current 48 hour security embargo on the release of precise satellite ephemeris information to civil users should be re-examined.
- Additional GPS monitoring stations should be added to the existing operational control segment. Cost & comparison studies should be completed to determine if Defense Mapping Agency of U.S. Air Force sites should be used.
- The operational control segment's Kalman Filter should be improved to solve for all GPS satellite clock and ephemeris errors simultaneously through the elimination of partitioning and the inclusion of more accurate dynamic models.
RAND
The RAND Corporation is a federally funded research group that focuses on national and military issues. The organization was formed to be a U.S. Air Force think tank studying nuclear weapons targeting issues in the '60s. RAND has several papers on GPS, some discussing the use of GPS for ballistic missile guidance. These papers may be ordered directly from RAND.See Also...