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“GPS is a humanitarian weapon system”

Jan 2010 | One Comment

says Dr Bradford W Parkinson, Chief Architect of Global Positioning System

Dr Bradford W Parkinson

Chief Architect of Global Positioning System
Dr Parkinson oversaw the Global Positing System (GPS) program from conception through development and verification as the first GPS Program director and is best known as the ‘father of GPS’.He received his BS in general engineering at the US Naval Academy in 1957, and his MS in aeronautics from Massachusetts Institute of Technology (MIT) in 1961. In 1966, he received his PhD from Stanford University in aeronautics and astronautics. He became the manager of the NAVSTAR GPS development program in 1972, finally retiring from the Air Force in 1978. As a Professor at Stanford he pioneered a number of first-of-a-kind demonstrations of GPS applications including Robotic Farming and Aircraft Blind Landing.
Dr Parkinson is the recipient of several awards, including the 2003 Charles Stark Draper Prize, the IEEE Sperry Award, NASA’s Distinguished Public Service Medal, and has been inducted into the NASA Hall of Fame.

Given the enormous impact that GPS has on our lives today, how does it feel to be referred to as the ‘Father of GPS’?

I am glad that you are asking this question, because it is my belief that there is no inventor of GPS. I certainly was the person that led the development of GPS, but if one goes back into history, there are two things that were really the foundation of what we did. In many cases the people involved, and what they did, has been totally forgotten.

The first was that, in 1964 to 1966 there was a study done by the Air Force’s 621B program. In it, under Jim Woodford, all the alternatives to achieving a new satellite navigation system were explored. We drew on that study and, of the alternatives he looked at, we picked the one that was most challenging but at the same time had the greatest benefit to users. This selected alternative was the four satellite, passive-signal, solution that eliminated the need for a user to have an Atomic Clock.

Secondly there was a lot of controversy on what type of signal we should use. Fortunately, by the time I advocated the GPS you know today, the Air Force had already run a series of tests using the PRN/CDMA signal and actually demonstrated that signal with aircraft at the White Sands Missile Range flying over transmitters of such codes. An alternative signal structure, known as Side-Tone Ranging, was deliberately rejected.

The Woodford study was originally classified Secret, and not generally known outside the GPS program. The study and the White Sands tests were the most fundamental basis for GPS. The resulting system is quite different from a proposed alternative that was patented in 1974; some 8 years after the Woodford study had been completed.

I had all the Secret Study and the test results when I decided what the architecture of GPS would be. Therefore, I was perhaps the chief architect and program manager, a leader and advocate, but inventor is not a word I like at all – I would like to set the record straight and credit the prior studies and developments.

GPS took time to evolve and there must have been many disappointments and hurdles in your journey, would you like to share some of those challenges with us?

The challenges came in a variety of ways. There were a number of technical challenges, and I will focus on one – making clocks. We all recognised that we needed to eventually put atomic clocks into space, but the radiation environment was quite intense. The Naval Research Laboratory had been working on space-borne clock technology. Based on their progress, I decided we could prudently design GPS with atomic clocks on orbit. Both NRL and the original 1966 Woodford study had recommended this. I tasked NRL to provide the clocks but they could not provide one that was robust enough in time for the first launch, and that was a disappointment.

As it turned out, it was an alternative clock that I had asked my satellite builder – Rockwell International (Dick Schwartz and Hugo Fruehof) – to develop, that actually flew first. There were several of these clocks on the first three satellites. On the fourth GPS satellite, a Cesium atomic clock developed by Bob Kern (a marvellous inventor and engineer) was included. This had been developed under the sponsorship of NRL.

Another aspect was the political challenge in keeping the GPS train on the track and keeping it supplied with fuel in the form of money. It was not an enormous amount of money: the first phase of the program was less than 200 million dollars – but the political challenge was in keeping that money flowing, in particular overcoming the lack of support by the Air Force.

The Air Force preferred to buy airplanes. Though some people did understand the value of the GPS system, by and large the leadership did not understand the payoff of precision weapon delivery so that was a very serious challenge.

Incidentally from the start we had always designated GPS as a military-civilian system. Some people think that the civilian access came along later; it did not- from day one it was a military-civilian system.

You have faced resistance and lack of cooperation in this journey, how did you keep yourself motivated to achieve what you have?

Actually that was never a problem. I had been allowed to handpick the officers that were working for me. There is a tendency in our country to think of military officers as not very smart, but the officers in my team were brilliant. There were three or four with PhD’s and all the rest of them had Masters Degrees from MIT or Michigan or Stanford or places like that. We had an outstanding Aerospace Corporation support Team, and excellent contractors.

As a result, in terms of motivation, we fed on each other. They looked on me a leader, but at the same time it was almost like a football team and the mark of a really good team is that nobody wants to let the rest of the team members down. As a result, the long hours, the intellectual content, the motivation was always there. This team composition enabled us to take on each challenge as it came and solve it.

You had ‘predicted’ some of the uses that GPS is put to today, are there any uses/applications that even you had not envisaged?

This is an excellent question. We could see the uses in general terms. Though there were many we missed, let me just point out three things that we did not envision.

We thought GPS would be extensively used for aircraft navigation. We did not realise it could be used for full category III aircraft blind landings using GPS alone. That was demonstrated by some of my Stanford students (Clark Cohen, Stu Cobb, Dave Lawrence et. al.) sometime back in 1992, so that was a surprise. The second total surprise was robotic farming. Right now GPS Agriculture is a business worth more than 400 million dollars a year worldwide and growing. Again, with some of my Stanford students – Michael OConner, Tom Bell and others, we put together the first robotic farm tractor that was able to pull an implement on a rough field with an accuracy of about 4-5 cm. The John Deere Company helped us do this and it was more accurate than the best driver that they had.
We had thought we could do survey to perhaps a meter. The third big surprise was that the GPS industry has shown accuracies, in three dimensions, to better than a millimetre. Key developers included Charlie Trimble who founded Trimble Navigation, and Phil Ward of Texas Instruments.

All three of these applications were enabled with the signal structure: with the carrier tracking receivers that relied on the PRN/CDMA signal that had been demonstrated by 621B at the White Sands Missile Range back in 1971; but we did not realize such accuracy was achievable. This has enabled the very accurate tracking of tectonic plates and earth movement.

GPS has already achieved so much, what could be the next thing that may happen in the near future?

I think that, with the additional satellite signals (Galileo, GLONASS etc.) we are going to have much better service, more robust, better accuracy, more wide-laning; and I can visualise robotic automobiles.

In my opinion, robotic automobiles are first going to come up simply as warning and guidance systems to the users. But then, we may have automobiles on the freeways that are measuring the distance between vehicles that are cooperating in fog or reduced visibility, to avoid collisions. Eventually, this could lead to automobiles that are actually being steered robotically by GPS. The farm tractor is a predecessor of that, and I understand, even today, Mercedes is actually doing this, where the autos go round and round, on their test tracks, completely under GPS control.

Do you think the apprehensions about GPS ‘failure’ are justified?

First of all, I think the notion that GPS would suddenly not work is fairly far-fetched. I have dug into that a great deal. What is more apt to happen is that for some reason or another we may have premature failure of the satellites and hence we may not have as dense a population of them.

We would call that a brown out. I do have some concerns about that, but I don’t think under any circumstances it is going to disappear. I am very anxious to see the first IIF be launched and I am anxious to see USAF JPO make progress on GPS III. I will be visiting the manufacturer here to get an assessment of that. I still serve on an Independent Review Team for the Department of Defence on GPS, and we help evaluate risks.

I think the probability is that we are not going to have as many satellites as we currently enjoy. The US commitment is for only 24 (there are currently about 30) – I believe that commitment can be met, but there is some risk. The current GPS Program Director, Col. Dave Madden is outstanding.

Please share your views on the eLoran program, which was seen as a valid ‘backup’ for GPS, but has been terminated now?

I was the chairman of a study by the Department of Transportation to review the need for enhanced Loran (eLoran). We were initially very sceptical, but we dug into what eLoran could do. It was not the Loran of old: it was quite an improved system and we concluded that in areas where the coverage was available it could do 30 to 50 meters or better. (Aircraft would need to use a barometric altimeter for the third dimension.)

Although eLoran would not be quite as accurate as GPS, if it was done right, one could take the eLoran plus your altimeter, feed them into your instruments and have a smooth transition in the event something happened to the GPS signal- particularly local jamming.

The possibility of local jamming is certainly there and occasionally it has happened. So, if people were to want to do that maliciously or deliberately, having eLoran as a backup would deter such action. The point being that if they jammed GPS, it would make little difference for most applications, and they would not see a payoff for such an illegal activity.

I think eLoran is an excellent backup though it does not cover the world, but it covers many of the areas where you have intense dependence on GPS for safety of life applications. The investment is small, the yearly cost of running an eLoran system is somewhere around 30 million dollars and relative to everything else we are doing it is absolute peanuts. Cancelling the eLoran program is a very, very bad decision.

What is your opinion about the upcoming GNSS systems around the world?

First, I am an advocate for all of those systems and am very enthusiastic about them. I think it will be a great benefit to users to have these other systems deployed. I have gone on public record advocating Galileo. Candidly, when they first proposed Galileo, thinking they were going to do it in 4-5 years; I said No way! Do not underestimate the complexity of what you are doing; having said that, I still wanted them to do it.

Now, my guess is that the political support to do these things is going to waver as people discover it is not so easy, it takes a lot of effort. But, I would not characterise it as a race in the ordinary sense. I think what is important is that these other systems are all made to work seamlessly with GPS so that the user on the ground can benefit from a much larger constellation and allay any fear of brown outs.

What do think has driven so many countries to develop their own GNSS systems?

Well first of all there is the issue of robustness and putting all your eggs in one basket – that is one aspect and a major legitimate concern.

The other, is a matter of national pride. In Europe there is a feeling that GPS dominates things. The national pride also relates to perceived economic benefits.

Last, GPS has a signal that is used for our military and allies. I think in some cases other countries would like to have such a signal. The military aspect and having control of a GPS-based precision weapon delivery system is just part of the way the world operates. I think the reason the Chinese are developing Compass, more than anything else, is to support their military, though I am certain they are going to make a portion of their system available for civil use as well.

The advantage of GPS based weapon delivery is that if the target is accurately located; you hit the target, you do not hit the nearby mosque, or church, or temple, or hospital or whatever. I sometimes shock audiences by saying that “GPS is a humanitarian weapon system!” By that I mean you do not hit things you do not want to hit.

I think all those are reasons to develop additional, GPS-like, systems. Though it is ultimately a political decision made by you in India, the Japanese etc, but I will forecast that it is more expensive than most people think.

Can GPS be selectively switched on and off by the US?

Of all the countries in the world we are the most dependent on GPS, and as a matter of fact the new satellites do not even have such a capability. Disrupting the signal would be very dangerous to our own citizens. Earlier, the US used a technique called Selective Availability (S/A) to deny use – by simply wiggling the timing on the signal. The use of WAAS, the use of EGNOS and the use of the other differential overlay systems like the one the Indians are building all completely remove the effect of any such ‘wiggle’.

Just before the first Iraq war, the US had turned on the GPS Selective Availability feature. But the irony was that, as soon as the war started, they decided to turn it off since many of the soldiers had civilian GPS sets. It was hurting themselves. We never should have done it in the  first place.

Incidentally, I was very instrumental in getting that turned off; my argument always was that wiggling the signal with selective availability was only going to speed up the introduction of differential systems and that is exactly what happened. By 1978 we had already demonstrated differential GPS that could reduce errors to about 2 meters, so I said why on earth would you try and put something in place that is so trivially defeated.

Then, the great irony in the United States was that the United States Coast Guard put together a system of marine beacons that was taking that error out, even before WAAS. So you had one group in the government putting the error in and another group of the government taking it right back out.

Is there any application of GPS which you think has had a negative impact for the users?

Let me mention two things here. First of all I love GPS, but the total dependency on GPS, particularly for safety critical applications, to me is a mistake. That is the reason I like eLoran as a backup. We could have other backups too, but eLoran is virtually unjammable. So I think a generalised negative is that too much dependency leads you down a somewhat risky path.

Second, is this Big brother system of tracking people or vehicles without their knowledge. I can understand law enforcement doing that. I can perhaps also understand a parent tracking his teenaged daughter. I do not endorse it, but I can understand why they might want to do that. This aspect of tracking people is problematic and sort of uncomfortable for us in this country and I suspect it would be in other countries as well.

With everything going digital, do you think hardcopy paper maps still have a relevance in our lives today?

I am a map freak and I love maps – that is my emotional response. There are certain situations where GPS cannot help, for example as I sit up here in the mountains and gaze out at other mountains on the distant horizon, I need a map to know which peak I am really looking at.

I always get back to this total dependence on GPS, I think the map is a logical backup for many users. In particular, you hear about people accepting car routes, that take them into the wilderness and the next thing you know they are isolated; that was because they did not look at a map. GPS can tell them where they are but it is a different technology that tells them where they should go. Certainly map technology can be stored electronically, but on the other hand having a crosscheck with a paper map and using your common sense is pretty important too. So I hope there is always going to be a place for paper maps.

Could you please tell us about the NASA-funded Gravity Probe B program at Stanford University.

I am a Co-Principle Investigator on the program. Started back in 1961, Gravity Probe B is the longest running program at NASA and Stanford University. It went through enormous political and technical difficulties, but we finally launched the satellite in April 2004, putting into orbit four gyroscopes.

The spin axis of a perfect gyroscope, if one considers Newton’s Theories, would stay pointing the same way forever. Einstein said something different. His theory implies that as the gyro orbits a body, such as the earth, the space-time fabric is distorted and it is distorted in such a way that every time it orbits the earth the spin and axis of this perfect gyroscope will actually be seen to move. This change in direction is predicted by Einstein’s General Relativity theory, but the effect had never been seen before. We launched four gyroscopes in space and have seen the effect – verifying this predicted effect – to about 0.3 percent or better. I believe this is the most accurate test of Einstein’s theory ever.

There is a second effect that is much more subtle. The rotating earth actually drags space and time with it almost like it was a viscous fluid. This effect is incredibly tiny, being on the order of 70 milliarcseconds per year. A milliarcsecond is the width of a human hair at 10 miles. We have now also measured this second effect to better than 15%. The final results are due out sometime in 2010, but the interim results have already generally been available (

The purpose is that all of the fundamental theories, including General Relativity or Newton’s Gravity, are subject to modifications. You can test them to a certain point and then you run into a discrepancy. An example is the Michelson-Morley experiment, where the speed of light seemed wrong. It was Einstein who proposed the answer to that in Special Relativity.

The same is true of General Relativity and physicists know that General Relativity is going to have to be modified because it does not fit in with the other laws of the universe – the strong and weak nuclear forces, and electromagnetism.

Therefore the point was to try to ascertain if there is some weakness in this particular area of the theory that would act as a pointer to the theoretical physicists as to new modifications to the General Relativity Theory.

Gravity Probe-B has been a very long, very arduous journey. I was program manager for 8 or 9 years facing some of the most difficult technical challenges and I will say the Program is a tribute to the perseverance of the Stanford physicist Francis Everitt. He is the one who kept rescuing the program when it was threatened with cancellation. But, today we now have results with marvellous precision to calibrate how well we understand Einstein’s theory.

A word of advice for the nations working towards their own GNSS systems?

Let me think about that. Well, the most important thing is tenacity. Along the way other developers are going to run into all kinds of obstacles – political, technical, the market will push back at them, one thing and another – if they are going to succeed they have to have tenacity.

GPS: Myth and facts

  • There is no ‘inventor’ of GPS; it is the culmination of the efforts of many people.
  • The GPS system design was fundamentally based on an extensive, classified, Program 621B study from 1964-1966, and a signal structure verified with 621B tests at the White Sands Missile range in the early 1970s.
  • From the start GPS was a military-civilian system.
  • Many applications that GPS is used for today had not been envisioned.
  • Under no circumstance is GPS going to ‘disappear’.
  • Cancelling the eLoran program as a backup for GPS is a bad decision.
  • The civilian signal of GPS is just as accurate as the military signal.
  • The GNSS systems cost much more than people expect.
  • GPS cannot be selectively switched on or off.
  • GPS cannot replace common sense!

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One Comment »

  • haubold said:

    Dr. Parkinson,

    We did appreciate very much your perception of GPS and beyond in this article.

    The International Committee on Global Navigation Satellite Systems (ICG) was established in 2005 under the umbrella of the United Nations. A seminal achievement of the Providers Forum consisting of US, Russia, EU, China, Japan, and India; all of them operating their specific GNSS. For a long time, surely the main goal of ICG will remain to be compatibility and interoperability of the 6+ systems.

    How do you perceive the establishment of ICG and its prospective ability to improve GNSS services world-wide with a kind of “one signal produced by many GNSS systems”?

    Very sincerely yours,
    Hans Haubold

    Professor Hans J. Haubold
    UN Office for Outer Space Affairs
    Vienna International Centre
    P.O. Box 500, A-1400 Vienna, Austria

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