Navigational stars in the sky

This is the sixth in a series of articles looking at the impact of NextGen on GA pilots.

Over the last six months, we have demonstrated how aviation history has contributed toward the development of our National Airspace System, including new technologies and procedures yielding a safer and less expensive way to fly. Every step of the way has been a major leap, not only on the side of safety and operations in this aeronautical equation, but also benefiting the industry and aviators by incorporating current-day technologies.

We started with bonfires and slowly graduated through electric visual aids and finally to radio navigation, with the use of state-of-the-art electronics available at each point within this aeronautical time line. This will eventually culminate in the developing Next Generation Air Transportation System, known as NextGen.

However, now we turn the pages way back — and I mean way back — so far back we meet up with our early mariner explorers who used stars in the sky to get from point A to point B. We find that they, too, had a GPS system to guide them. Of course, they weren’t man-made stars like our current-day satellites, but these early explorers used distant stars to calculate their locations practicing a technique known today as triangulation.

Many would agree that today’s GPS technology is new and gives us the ability for pinpoint accuracy never achieved before. But is this correct?

GPS technology was first introduced by the U.S. Department of Defense (DOD) with the help of Dr. Ivan Getting, a graduate of the Massachusetts Institute of Technology (MIT). Getting practiced his skills in astrophysics working for Raytheon in 1951 developing an earlier tracking system — or GPS — for the DOD. So GPS isn’t that new after all! Getting designed a system using a three dimensional time differential measurement technique to determine the locations of InterContinental Ballistic Missiles (ICBM) when being transported over rail.

In 1957, at Johns Hopkins University, two American physicists, William Guier and George Weiffenback, decided to monitor the launch of Russia’s Sputnik satellite, the first orbiting satellite in history. By using Doppler Effect — the same Doppler we discussed in the last installment of this series — in conjunction with the signal strength of Sputnik, the duo could calculate exactly what Sputnik’s orbit was. It was not as if this observation was that incredible with what we know today, but in 1957, this was esoteric as hell and totally analog.

By monitoring this over time, the signal strength and Doppler Effect would increase and decrease depending how far Sputnik was away from the receiving location (See Figure 1). This proved that Sputnik’s exact orbit (or sphere) could be determined by simply monitoring the signal strength and Doppler Effect of its transmission.

It was not until 1973 that GPS was actually deployed, supporting the military, primarily the Air Force and the Navy. The process took more than three years to develop by using Pseudolites or Pseudo Satellites that were ground-base transmitters at local positions. [We will come back to this as we move into WAAS (Wide Area Augmentation System) later in this series.]

These types of transmission systems are still in use today to simulate ground-based satellite navigation, allowing for a completely controlled network of Pseudolites. With these types of systems, further design ideas can be encouraged for other types of aviation and tracking, such as tracking and navigating on distant planets. These self-calibrating pseudolite systems can be arbitrarily placed on the surface of other planets. This advancement allows for an entire navigation system for robotic machines (Rovers) and drones on other planets and distant worlds. By simply varying the transmitter’s output — generally using output levels in the micro volts (.000000001 volt) range — these systems can replicate different distances, just like the boys from Johns Hopkins did with Sputnik. These systems are known as Self-Calibrating Pseudolite Arrays (SCPA).

Figure 2 demonstrates how these Pseudolites can be placed and used for pinpoint accuracy. Figure 2A shows how triangulation can be used to calculate a location. However, in Figure 2B, notice that we have replaced the lines with spheres. Although used in a different configuration, you will soon see how these spheres play a big role in GPS and in the way it will work with NextGen under Automatic Dependent Surveillance-Broadcast (ADS-B), the cornerstone of NextGen.

After successfully experimenting with pseudolite ground-base systems, GPS was ready to take to the sky by launching 11 satellites (or pseudostars) placed in strategic locations in orbit around the Earth. These 11 GPS satellites were later increased to 18, allowing for even better accuracy, which allowed the U.S. to directly monitor the Soviet Union’s nuclear testing activities, according to the 1963 agreement with the USA to cease nuclear testing.

Up to this point, all satellites were put into orbit by the trusty Delta Rocket used through the years by NASA. With a higher demand for accuracy, the plan was to launch more satellites with the help of the Space Shuttle program, only to be stopped after the Challenger disaster in 1986. With a major interest into what the Soviet Union was doing with its missile program and the shooting down of Korean Flight 007, it was obvious that more GPS satellites needed to get into orbit, forcing the continued use of the Delta Rocket program. This move increased the quantity of GPS “stars” to 24, allowing for continuing surveillance around the world.

Next month we will provide even more details on how GPS calculations are made and how using ground base pseudolites makes for the increased accuracy of WAAS, a big player in the NextGen system.

Jeffrey Boccaccio is a private pilot and chief engineer at MatchBox Aeronautical Systems ( You can reach him at or


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