Letters to the Editor

July 1, 2010  - By

Our readers respond to the cover features in the April, May, and June issues: the two-part special the “Origins of GPS” and Richard Langley’s look at “GPS by the Numbers.”



Source: GPS World

Spilker and Parkinson: from GPS Origins to L5

Thank you so much, Brad, for the recognition you gave me in your history of GPS origins in the May and June issues.

I keep in my sometimes near photographic memory the numerous hours and trips we made over these many years, especially in the early days when you were Joint Program Director of GPS, the meetings we had with Bob Cooper and the Navy admirals. You

offered me the opportunity of a lifetime to contribute a little.

The one thing that you did not mention because of modesty is your ability to put together a team of Air Force officers so outstanding that I have not seen a comparable group anywhere else.

There is at least one other contribution worthy of inclusion, later in the program. One day during a board meeting at Stanford Telecom, I pointed out to Bill Perry that Congress had just zeroed out the GPS budget. He immediately got on the phone to the chairs of the House and Senate Armed Services Committee. Sam Nunn was chair for the Senate, and after much work and many calls, talked them into reversing that decision.

I have often thought that had the two parallel Navy Timation and Air Force 621B programs not been folded together as a single joint program, neither program would have survived.

On another subject, I think there is still work to be done on precision interoperability of multiple GNSS. How does it relate to “bounded inaccuracy” and integrity and precision positioning and carrier-phase precision?

Finally, many probably do not know it, and I have not received any recognition for it, but the work I did in designing the GPS L5 signal was performed as a gift to the U.S. Air Force, Federal Aviation Administration, and our country, with no compensation of any kind including my travel to the ION conference where I gave the award-wining L5 paper with AJ Van Dierendonck.

[See J. J. Spilker and A. J. Van Dierendonck, “Proposed New Civil GPS Signal at 1176.45 MHz,” Proceedings of ION GPS-99, Institute of Navigation, and an earlier, similar paper at the June 1999 ION Annual Meeting. — Ed. ]


Source: GPS World

I only mention it now because of the successful Block IIF launch. I ask nothing in return, and only hope it is of some value to our country and the world.

— Jim Spilker, Jr.
Half Moon Bay, California

Brad Parkinson replies:

Thanks to both you and AJ. It will be an outstanding addition to civil (and I hope military) options. Thanks also, of course, to the groups that ironed out the myriad of important details.

You also deserve credit for the initial work on split spectrum. Recall we suggested it for the civil signal to attain separation, and it was immediately endorsed and selected as the basis for the military L(M) signal.

— Brad Parkinson
Palo Alto, California

Selling GPS

Reading your two-part history of GPS origins recalled another story about those early years, and an influential Air Force officer.

Major General George Keegan was one of the most interesting people I met in my 35 years of Air Force civil service. Primarily an intelligence officer, he was considered one of the leading authorities on the Soviet Union, had been military attaché in the American Embassy in Moscow, and had just been given interim assignment as Director of Plans and Programs, HQ Air Force Logistics Command. He probably did not know anything about logistics, but he had a large staff to help him.

It was soon evident that he liked to come out to California, ostensibly to see his troops there (my office). What he really wanted was to go to the RAND Corporation in Santa Monica, the first non-profit brains factory set up in 1946 to guide the military services. RAND had a group of retired generals and admirals who war-gamed all sorts of scenarios to test various plans and to critique experiences leading to recommendations for changes. This was stimulating and valuable to him.

I was in charge of arranging his visits, and he was highly interested in the programs underway and especially in development at the Space and Missiles Systems Organization, where I worked. I would arrange briefings for him and occasionally drive him to our offices outside Norton Air Force Base near San Bernardino where the ballistic missile programs were developed.

We were collocated with the SAMSO Development Plans shop on the 4th floor of the Aerospace Corporation headquarters building when he called to set up a visit. He asked me what he had not been briefed on. I thought of one program, then called 621B, and told him it was a study area with a lot of promise. He asked me to set it up.

The “Program” was one lieutenant colonel in an office up the hall from us. He was managing several contracts to explore and develop the concepts for operation and conceptualize the hardware for development of what is widely known now as GPS.

The lieutenant colonel, whose name is lost to me, was not enthusiastic about briefing Gen. Keegan. I told him he was going to be on the Air Staff, he had security clearances for everything, and he would be smart to accommodate him. He agreed, but obviously reluctantly.

When General Keegan arrived, the lieutenant colonel started to describe the program as then projected. Gen. Keegan was obviously excited at what he was hearing, and he started throwing questions.

As a little background, knowing where you are precisely and being able to use that information is one of mankind’s oldest problems, and for the military forces, it is of the highest value. Among the many guidance systems in the inventory were Loran, OMEGA, TACAN, and many others. The annual costs to develop, maintain, improve, and operate these ran into hundreds of millions if not billions of dollars, and all of them operated with severe limitations.

General Keegan asked, if 621B were developed and deployed successfully, would it supplant and obviate the need for Loran? He got an extremely reluctant answer, yes. Would it replace TACAN? Same answer. OMEGA? Same answer.

I remember him sitting there staring at a very discomfited lieutenant colonel. He said, if I recall his words correctly, “Colonel, you don’t know what you have here. I don’t think you realize its importance. I will just have to sell it for you.” Later, when the General had left, the lieutenant colonel asked me if he was kidding. I replied that, from what I knew of him, he meant what he said.

Fast forward now about two years. General Keegan was the Intelligence Chief, HQ U.S. Air Force. Program 621B had progressed, had several people in the development planning process, and was ready to expand greatly if funding were provided by the Department of Defense. It was in competition with many other Air Force, Navy, and Army programs, and there wa
s no assurance that all would be approved.

At that time, possibly even today, there was an annual Department of Defense conference to allocate funds called the Defense Systems Acquisition Review Committee, or DSARC. Each agency presented its case. The 621B program chief was there (I now recall him to be Col. Parkinson, from reading the article), and he came to see us after the meeting in Washington. He was euphoric, and he wanted to know who General George Keegan was. I told him of the briefing I had arranged with his predecessor several years ago, and what Keegan had said. He said General Keegan had come through in spades.

This is second-hand reporting, but what happened was that before the DSARC began, General Keegan, who was not a member, asked the chairman for permission to address the group. What he said was something like this:

“Perhaps once in your lives, if you are extremely fortunate, you may have the opportunity to influence a development that may truly benefit your country. Today you have an opportunity to foster a program that will not only be of enormous value to all the armed services, but provide the answer to one of man’s oldest problems. Program 621B will give the military capabilities that will surpass anything ever imagined, and give the civilian world a spinoff of obvious immediate value and unlimited future potential. Whatever else is approved today, this program should be considered vital.”

The program director said General Keegan’s remarks were delivered with passion, and when he had finished and left their room, everyone looked at each other. He said their presentation was made easy — they were asked a lot of questions, and they had the opportunity to fully describe the timing, the impact, and the significance.

The result was they were not only fully funded, but they were told that if they could use more funds later, to let them know. He said after that speech, there was no question in anyone’s mind that there would be a wide open road for their program.

One of the rewards of my job in those years was being aware of and sometimes, in some way, involved in many fascinating events and programs. In this case, I inadvertently set in motion a chain of circumstances that, in a small way, may have facilitated the development of one of the most rewarding developments that came from the space and missile programs of the 1960s, ’70s, and ’80s.

I did not sell GPS, but, unknowingly, I helped.

— Don Hallwerck
Long Beach, California


Source: GPS World

Let Me Count the Waves

I read your publication with great delight but little understanding — with the possible exception of Mr. Langley’s contributions, especially “GPS by the Numbers” in the April issue. Fiddling with my calculator years ago, I quickly found pi to eight digits using 355/113. Do you suppose Mr. Langley has a better simple m/n?

— John Woodcock
Bellevue, Washington

Richard Langley replies:

Thanks for your message and kind words about GPS World. Fraction approximations to pi is an interesting topic, one that I didn’t have much room to write about in the numbers article. Your use of 355/113 as a good approximation for pi is one that has been known for awhile. It was first discovered by the Chinese mathematician, Zu Chongzhi in 480 A.D. It is good to seven digits. You need more than an 8-digit calculator to show this, though. Type 355/113 into the Google searchbox to get an answer to 9 digits and you’ll see that only the first 7 are valid. It’s somewhat more complicated, but the fraction 103993/33102 gives pi to 10 digits. These fractions can be derived from the continued fraction representation of pi. For a discussion of that and many other interesting facts about pi, see Wikipedia.

I have received the latest issue of GPS World. What a remarkable accomplishment! An outstanding example of sustainability, commitment, impact, and excellence! The Innovation column has constantly been a source of inspiration and ideas for all, not least GNSS students around the world.

If ever you have the chance to collate them in one single pdf file and put it on your website or/and that of GPS World, this would be a most valuable contribution and worth more than many books on the subject I can think of!

Congratulations, and may we see you on the front page for the 300th column!

— Gerard Lachapelle
University of Calgary, Canada

Just read your “Numbers” article. I enjoyed it very much, especially because I am writing java code for an SDR-GPS-receiver I am building. As a starter I am trying to decode Kai Borre’s data file. I just finished implementing parallel code search using FFT. Gives remarkable insight in DSP. I am a retired engineer and radio amateur PA1KDG. Keep on writing and I’ll keep on reading — promise.

— Kees de Groot
Wageningen, The Netherlands

Richard Langley replies:

Many thanks for your message and interest in the GPS World Innovation column. Coincidentally, one of my students has just finished up a Ph.D. project on designing a strategy for implementing a SDR-GPS receiver and presented his results in April. Good luck with your project.

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