Federal Radionavigation Planning

The Federal Government operates radionavigation systems as one of the necessary elements to enable safe transportation and encourage commerce within the United States. It is a goal of the Government to provide this service in a cost-effective manner.  As the full civil potential of GPS and its augmentations is realized, the service provided by other Federally provided radionavigation systems is expected to decrease to match the reduction in demand for those services. However, operational or safety considerations may dictate the need for complementary navigation systems to support navigation or conduct certain operations. While some operations may be conducted safely using a single radionavigation system, it is Federal policy to provide redundant radionavigation service where required. A major goal for the US Government is to select a mix of common-use civil/military radionavigation systems that meets diverse user requirements.

Executive Summary

The Final Report of the President’s Commission on Critical Infrastructure Protection

concluded that Global Positioning System (GPS) services and applications are

susceptible to various types of interference, and that the effects of these vulnerabilities on

civilian transportation applications should be studied in detail. As a result of the report,

Presidential Decision Directive (PDD) 63 directed that the Department of Transportation

(DOT), in consultation with the Department of Defense (DoD), undertake a thorough

evaluation of the vulnerability of the national transportation infrastructure that relies on

the Global Positioning System.

The Volpe National Transportation Systems Center (RSPA/Volpe Center) conducted a

vulnerability analysis of GPS and identified the potential impact to aviation, maritime

transportation, railroads, and Intelligent Transportation Systems (ITS). The final report,

series of recommendations, which were reviewed and ultimately accepted by the

Department’s operating agencies. Recommendation sets were made relative to:

overarching issues related to GPS vulnerabilities, mitigating the vulnerabilities of the

GPS signal to disruption or loss, and mitigating the vulnerabilities of the transportation

systems resulting from the disruption or loss of the GPS signal.

Addressing this set of Volpe recommendations started with the key question, “What type

of backup systems must be in place to mitigate the disruption or loss of GPS?” The

answer led to the establishment of a Capabilities Assessment Task Force to develop a

recommended capabilities investment strategy for US radionavigation systems to meet

transportation infrastructure requirements for the next ten years. This recommendation

had to balance the plan to move toward a heavy reliance on satellite navigation with the

vulnerabilities of such an approach highlighted in the Volpe Study. According to the

study, “Backups for positioning and precision timing are necessary for all GPS

applications involving the potential for life-threatening situations or major economic or

environmental impact … The appropriate mix for a given application will result from

careful analysis of benefits, costs, and risk acceptance.”

To accomplish the analysis the Task Force focused on two tasks. The first task was to

conduct a multi-modal capabilities assessment of all radionavigation systems, both

current and planned, to satisfy the national need for radionavigation, positioning, and

timing. This included looking at the possibilities of using a system designed for one

operating agency as a backup for the needs of another. The output of this task was a

technical and cost perspective on the five most promising alternatives for system

architectures (or systems of systems). This output was the input for the second task,

which was to assess a set of alternative systems considering additional factors. These

factors included recommendations of the Volpe report on backups to GPS, potential

impact on other US Government agencies’ systems and operations, user equipage, and

interagency and international agreements. The final objective was a recommendation to

the Secretary on the most appropriate mix of radionavigation systems, from both a

capability and cost perspective, to satisfy the national need for radionavigation,

positioning and timing services for at least the next 10 years.

There are thousands of potential combinations of radionavigation systems. The Task

Force initially narrowed the field to eleven potential options by focusing on four crosscutting

radionavigation systems. These systems provide potential multi-modal

capabilities and have the greatest impact on the radionavigation system tradespace.

These systems are Loran and the GPS augmentations: Wide Area Augmentation System

(WAAS), Nationwide Differential GPS (NDGPS), and Local Area Augmentation System

(LAAS). The Task Force explored the ramifications of removing individual systems.

This included identifying what modal requirements could not be met and what systems

enhancements might be possible to meet those requirements. As a result, the Task Force

developed four alternative radionavigation mixes that could address the current user

needs for primary and backup systems. This includes two baseline options derived from

the 2001 Federal Radionavigation Plan (FRP) with and without Loran, and two

collocation options with and without Loran. However, not all four alternative mixes may

address potential future requirements. As requirements and applications continue to

evolve, each operating administration must ensure that adequate backups are available.

Cross-modal radionavigation systems must likewise be carefully coordinated. The

current collocation and synergy of NDGPS with the Continuously Operating Reference

Stations (CORS), Maritime Differential GPS Service (MDGPS), and the GPS Surface

Observing System (GSOS) has already avoided significant capital construction costs.

The potential for future collocation of WAAS, NDGPS, and Loran facilities should be

explored in conjunction with any future expansions of those systems.

The Task Force recommends the following:

Department should review the overall radionavigation system program strategy to

ensure these systems meet the positioning, navigation, and timing requirements

across the entire transportation infrastructure in the most cost-effective and efficient

manner.

broadened to serve this function for radionavigation system programs. This

would additionally require expanding the membership of the IRB to include the

Under Secretary of Transportation for Policy as a voting member.

signals, should proceed as expeditiously as feasible in order to meet a multitude of

civil applications and safety-of-life missions that are critical to our transportation

infrastructure.

implementation schedule for these new GPS capabilities.

provide the performance to support aviation Non precision Approach (NPA) and

maritime Harbor Entrance and Approach (HEA) operations.

criteria, and is cost effective across multiple modes, the Federal Government

should operate Loran as an element of the long-term US radionavigation system

mix.

effective across multiple modes, the Federal Government should operate the

system only to the end of 2008 to allow users sufficient time to transition to

alternate navigation aids.

Loran evaluation, as follows:

Augmentation System (WAAS) to meet marine requirements.

the High Accuracy Nationwide Differential Global Positioning System (HANDGPS)

to meet surface (i.e., highway, rail, and marine) requirements.

to meet precision approach requirements for aviation.

conjunction with any future expansions of those systems, contingent on the results of

the enhanced Loran evaluation and benefit-cost analysis.

implemented in accordance with the schedule presented in the 2001 FRP.

radionavigation systems to contribute to the overall radionavigation mix should be

periodically evaluated.

This document is composed of the following sections:

Radionavigation Systems Task Force. It summarizes events leading to the preparation of

this document and tasks that were conducted under this study.

summarizes current radionavigation systems as well as future potential radionavigation

systems under research & development.

technical approach used by the Task Force. It lays out the system requirements for

transportation and non-transportation users and compares them to the capabilities of each

radionavigation system.

alternative radionavigation system mixes and how they were evaluated and down

selected to 3 alternatives mixes and a baseline.

radionavigation systems.

mixes recommended by the Task Force. This includes a baseline and 3 alternative

mixes.

Loran-C decision and recommendation from the Task Force.

systems.

conclusions and recommendations.