‘GPS + eLoran Greater than Sum of Parts’ – Dr. Gene McCall
Editor’s Note: Dr. Gene McCall makes several excellent points in the below article about the need to focus on an architecture that will ensure delivery of PNT services. He very much reinforces our Protect, Toughen and Augment message.
Dr. McCall also discusses synergies from integrating GPS and eLoran signals to provide much better service than either system could provide on its own.
Our readers will find the background information that Dr. McCall provides, as well as his thoughts about the way ahead, very interesting. DG
Assured Position, Navigation, and Timing for the United States
Posted by American Center for Democracy www.acdemocracy.org
By Dr. Gene H. McCall*
Sunday, December 18th, 2016 @ 5:51PM
Left: World map showing the location of GPS ground components
It is shown that the issue associated with assuring position, navigation, and timing is not one of building backup systems to augment the GPS, but, rather, one of designing and building a reliable overall PNT architecture.
I – Introduction-
Much has been said, recently, about the need for adding a nationwide system to compensate for the shortcomings of the Global Positioning System(GPS). It will be shown below that what I define as discrete system thinking is likely to lead to disappointing performance and high cost. We need to discard the idea of one system replacing another, and, rather, develop ideas that will guarantee adequate, and continuously improving Positioning, Navigation, and Timing capabilities for the nation independent of the components that comprise the architecture.
II – The Current Situation –
Since the Global Positioning System became fully operational in April 1995, the nation has relied more, and more, on it to provide essential position and timing functions throughout the United States. Some claim that the order for civilian use of GPS was mandated by an order from President Reagan following the Soviets shooting down a Korean airliner, KAL007 after it strayed into Soviet airspace as the result of a navigation error. President Reagan’s decision was announced at a daily White House press briefing on 16 September 1983, but there appears to be no record of an executive order to that effect unless it was part of a classified order which was never released.
The press statement also proclaimed that the system would become operational in 1988, seven years before Full operational capability was declared in 1995. President Clinton declared GPS to be a dual-use system to be made available to civil users on March 29, 1996, and, at the same time, announced the addition of a new civil signal on the L2 frequency.
On May 1, 2000, it was announced that the clock dither called selective availability (SA) which had been used by the military to limit GPS accuracy to, approximately, 100 meters for civil users would be discontinued. At the time that it was discontinued, selective availability, practically, did not achieve its goal of completely limiting civilian accuracy. At little additional cost receivers could be bought equipped for the detection of U. S. government-supplied signals, such as WAAS and the Coast Guard differential system, that were effective in removing the effects of SA. Thus, the government developed, and funded, systems that defeated its goals. Certainly a bizarre situation. After SA disappeared, though ordinary civil users experienced a noticeable jump in accuracy, and the use of the GPS signals throughout the world increased rapidly. Some government systems, such as the SA defeating signal associated with WAAS and the Coast Guard system, became redundant
Today many essential services, which make our nation a modern society, depend on GPS. Timing synchronization for cellphone networks depends on the signals. No GPS, no cellphones! Timestamps for financial transactions and phase locking of national electric power networks also find the system essential. Most precision aircraft instrument approaches throughout the country, which facilitates operations in poor weather, are GPS-based using the FAA Wide Area Augmentation System(WAAS). As of April 2015, there were 3543 such approaches in the United States, and the FAA is no longer installing self-contained instrument landing systems. The WAAS system is more reliable than the self-contained system and does not have some significant failings, such as sensitivity to snow reflections. Without WAAS, 983 airports in the country would have no precision approach. One should keep this fact in mind when proposing backup systems for GPS.
The remainder of the world has similar situations. Some, such as the Europeans, Russians, and the Chinese have responded by designing and fielding similar satellite systems under their national control, but, as yet, those systems have produced neither the performance nor the reliability of GPS.
In a way, the universality of uses of GPS has taken the government of the United States by complete surprise. Certainly, there were no plans for it to happen, and there is no coherent policy throughout the government bureaucracies which defines a way of dealing with it.
It is no wonder that many government agencies are now attempting to distinguish themselves as the primary agency for deciding what to do about assuring the future of essential Positioning, Navigation, and Timing (PNT) capabilities. The problem, now, is to make the suggested policies constructive, rather than destructive.
III – Real and Perceived Problems and Issues –