A Very Merry GPS Christmas

Articles about GPS, GLONASS, GALILEO, WAAS and other satellite navigation systems
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A Very Merry GPS Christmas

Postby jimh » Sun Dec 24, 2023 1:29 pm

December 2023 is an interesting time for the Global Positioning System, which has become such an essential part of boat navigation. I am old enough to remember boat navigation without any electronic aids, where I used just deduced reckoning to keep an estimated boat position between position fixes. I skipped the LORAN-C era, and got my first GPS receiver with integral chart plotter in 2003, over twenty years ago. The history of the Global Positioning System goes back over 50-years. Here is a recap of some of the most important dates, which all seem to have occurred in December or close to it.

About 50 years ago, on December 17, 1973, the Defense Systems Acquisition Review Council gave then U.S. Air Force Colonel Branford Parkinson approval to proceed with development of a satellite based navigation system, which would become today's GPS. Colonel Parkinson is now thought of as "the father of GPS", and he had to battle against a lot of bureaucrats in the Military to get GPS off the ground. In the next 12 years, GPS did get airborne, with ten GPS Block I satellites in orbit in the epoch of 1978 to 1985.

About 40 years ago, President Ronald Regan authorized use of GPS for civilian aviation, in reaction to the infamous shoot-down of a Korean commercial passenger flight KAL 007 by Russian military aircraft. (There is a fantastic article on this topic in Wikipedia, if you are too young to remember this. I remember that incident vividly, as I was working in a newsroom when it occurred and the first announcements of it came over the press wires. Everyone held their breath while waiting to see what action would be taken in response.)

Some historians note that the initial design of GPS seemed to anticipate dual military and civilian access as a basic feature, with the military in control of the system and able to use its highest accuracy (M-Codes), and civilian access available at lower accuracy (L1 C/A) and that accuracy also variable and under military control (Selective Avialibility).

The year 2023 is also the 30th anniversary of the achievement of initial operating capability, which is marked as arriving in December 1993. That epoch marked the first full constellation of 24 satellites in orbit and operational, and able to provide the standard positioning service.

Selective Availability was ended in May 2000 by the direction of then President Bill Clinton. Seven years later, In 2007, the government announced that its future generation of satellites (the GPS III series) would be constructed without the Selective Availability feature in their hardware.

As of December 2023, there are now six GPS III satellites in orbit and operational. An additional four GPS III satellites have already been built and tested, and are now awaiting launching.

The next GPS III satellite (GPS III SV07) is scheduled for launch in in the Summer of 2024, where the present plans call for the satellite to be sent into orbit by a United Launch Alliance VULCAN CENTAUR launch vehicle, still being developed. (The first actual flight of a UAL VULCAN CENTAUR is scheduled in a few weeks, on January 8, 2024, and let's hope it goes well.)

The next phase of GPS satellites, the GPS III F series of ten more space vehicles, are already being built.

More details about the creation of GPS, GPS III, and GPS III F satellites can be found in prior articles on GPS. See

GPS Designers Honored
https://continuouswave.com/forum/viewto ... =12&t=4233

GPS III Scheduled for Launch December 2018
https://continuouswave.com/forum/viewto ... =12&t=4066

SARSAT MEO 406-MHz Systems on GPS Satellites
https://continuouswave.com/forum/viewto ... 952#p23299