Thursday, August 30, 2007

Headline: GPS to replace radar

Guess who’s been smoking what? Many years ago when GPS [6] grew out of the Transit Satellite program [1], it became obvious that with a little work and faster computers, one could design a system that could tell a pilot where he was all the time. I started flying in 1971 and I realized that with a bit more computation, it could predict where the airplane was going. A bit more computation would display the difference between where the pilot wanted to go and the actual track across the ground. This would allow a pilot to follow a lubber-line to the destination. Nobody seemed interested because we had the VOR [3] airways system plus the newfangled LORAN [2] system. I wrote articles that nobody published. I foresaw the time that we didn’t need the old VOR equipment anymore.

We could use LORAN and some accelerometers and rate gyroscopes. All the information was available to accurately navigate an airplane to and from anywhere on the earth. Read about inertial navigation [8] in the references. What we needed were some electronic maps –that’s all!

Eventually GPS caught on. About the same time, most personal computers were being networked. Since I was designing networked equipment, I realized that we no longer needed ATC radar. [4] The FAA [5] had already required that transponders be operational in aircraft obtaining ATC services, so the same technology could be used to tell ATC where every aircraft to the radio horizon was. In fact, we no longer even needed to have our airplanes “painted” by radar.

We could install little boxes that, just like a network, transmitted messages in the blind, declaring who we were, where we were, and where we were going. The messages would be sent at 1 second intervals plus or minus some deliberate jitter to prevent continuous interference with other “in the blind” transmissions from other aircraft. The information would come from GPS receivers and, just like an Ethernet terminal in your computer, every transmitter would have its own unique ID. Every airplane so equipped, and of course ATC on the ground, would then know where every airplane within range was, simply by listening to those broadcast messages. I wrote about this also, but nobody published my writings, apparently thinking it was the mouthing of a fool. That was twenty years ago!

Latest thing
Now the “latest thing” is ADS, [7] Automatic Dependent Surveillance, and ADS-A. It’s similar to what I proposed twenty years ago, but much too complicated. Ground equipment should simply listen with a special receiver and airborne equipment should simply transmit in the blind on a special frequency, not shared with the existing transponders. That way, the migration path simply replaces obsolete equipment instead of replacing equipment with obsolete technology. Note that a GPS receiver only costs $69.95 retail. That's the expensive part of the aircraft component.

Protecting jobs
But how should I know? I’m just an Engineer, not some high-ranking ATC boss who needs to retain the obsolescence of the Air Traffic Control System to keep his job. I wonder if industry in general will ever listen to its engineers.

GPS will fail
It doesn’t matter. The “new” technology will fail miserably if there was an event that makes GPS satellite reception impossible, perhaps a solar flare or a deliberate jamming of satellite signals. At that time, the only thing that will keep airplanes separated is ground-based radar and some eyeballs. There have been several solar events that disturbed GPS navigation already. There will be many more.

Easy to jam
Furthermore, for “chump-change,” I could design and deploy a satellite jamming transmitter that would disable all GPS navigation horizon to horizon. I’m fairly sure an enemy could do the same. As Americans, we should not replace ATC radar with a GPS based system. Instead, we should use the new technology as long as it works, and fall back onto the old when it doesn’t. That’s the only way our flying public can remain safe.

ATC Radar replacement
New technology to replace ATC Radar is required and it doesn’t involve equipment installation within aircraft. All one needs is an emitter of UHF radio frequency energy that is guaranteed to remain on-the-air during power outages. It doesn’t need any rotating components, just some omni-directional peak power necessary to overcome path losses. This can be, but doesn’t need to be, co-located with an array of receiver antennas connected to a receiver with an appropriate multiplexer and A/D converter. The direction and distance from all the targets that reflect the transmitted pulse is resolved using a computer. Stationary targets are removed by software as well. This simple equipment could replace expensive and difficult to maintain electromechanical and vacuum tube technology currently in use. Nearly twenty years ago, Westinghouse demonstrated such a system using a local UHF television station as the emitter. Of course ATC shouldn't be dependent upon a private television station for operation. This was only a technology demonstration.

1. The Transit Satellite system
2. Long Range Navigation (LORAN)
3. VHF Omidirectional radio range (VOR)
5. Federal Aviation Administration (FAA)
6. Global Positioning System (GPS)
7. Automatic Dependent Surveillance (ADS)
8. Inertial navigation