Expert Advice: Looking Back to the Early Days of GPS

September 1, 2013  - By
Len Jacobson

Len Jacobson

By Len Jacobson

Besides my family and friends, two major influences have guided my life. One is GPS, and the other is flying, although I’m not a pilot. Most of the flying was on business trips for GPS. I’ve been writing a book about my experiences and how I helped in a small way to bring GPS to the world. I estimate I’ve spent about eight months aboard airplanes, logging almost 2.5 million miles. During that time, I visited many places throughout the world, acting as a catalyst to promote the use of GPS and to obtain GPS business for my employers and for myself. I kept an extensive log of my travels and it enabled me to recreate much of what happened, and my impressions of why events occurred.

In 1968, after two engineering degrees and five years working in communications systems, I met a business development director from Magnavox, which had teamed with Hughes Aircraft, where I worked, on a study contract. We both attended a briefing on the contract status; that day was my first encounter with what would become known as GPS.

I attended one more meeting about the 621B satellite program. The U.S. Air Force had no funding for a full-up 621B, so instead it focused on proving that the technology was viable. We were asked to bid on supplying a receiver that would precisely measure a half-mile of cable using a spread-spectrum signal. I vividly recall a Hughes VP stating that 621B would never go anywhere, and besides, Hughes was only interested in building synchronous satellites. Our 621B competitor, TRW, agreed take the follow-on contract. TRW was acquired by Northrop Grumman in 2002. The Air Force felt it needed two competitors in case one failed, so it offered a second contract to Magnavox. The company took the contract, which became its first hardware entry in the world of GPS.

Before long, I received an offer from Magnavox to join the world’s leading experts on implementing anti-jam communications systems using then-classified, direct-sequence spread-spectrum technology. Magnavox had been working in the field since it was formed in the early 1960s, building the first anti-jam modems for the Initial Defense Communications Satellite Program (IDCSP) and now pursuing a follow-on program. Its main business areas were satcom, tactical communications, and positioning programs such as the 621B receiver. There also was a group building Transit satellite receivers for the Navy. Transit was really the first navigation satellite, growing out of experiments at Johns Hopkins University Applied Physics Lab, using Sputnik signals to determine one’s position on Earth by tracking the Doppler signal of a satellite in a known orbit. Besides the Naval Research Lab, Magnavox built the only Timation receivers, an early competitor to GPS for solving military positioning needs using a satellite system.

While I was still working at Magnavox on satcom, the 621B receiver was completed and we proved you could use a spread-spectrum signal to accurately measure distance. Once again, the Air Force did not have funds to launch navigation satellites so it proceeded with a new effort called “621B User Equipment Definition and Experiments Program.” The prime contractor was Grumman Aircraft. The idea was to put four transmitters on the ground and have an aircraft with a receiver fly over them and try to determine the aircraft’s position. The signals were to look as if they came from four satellites and were received by an antenna on the bottom of the plane. Grumman decided to use a receiver built by Hazeltine, which had some experience in spread spectrum but nowhere near as much as Magnavox. For this reason, the Air Force leased another receiver from us, asking how much? We came up with the number $450,000, our development and build cost. They agreed, and we called the receiver the MX450. It flew beside the Hazeltine receiver on the NC-135 aircraft at the White Sands Missile Range. Most of the usable test data came from the MX450, showing residual errors between the aircraft solution and the range tracking system to be less than five feet. This data was crucial in getting DoD approval in 1973 to proceed with Phase 1 of GPS. But we should have called it the MX495 because we overran the cost by $45,000.

A Tale of Two Contracts

The procurement for Phase 1 GPS came together as two major contracts. There would be a small number of satellites that Rockwell would win competitively and would lead to many years and billions of dollars in future GPS satellites, as it became part of Boeing Corp. ITT would build its own payload and go on to be the major supplier of GPS payloads to this day. The other contract, a study contract, was awarded to three companies: General Dynamics Electronics (GDE), Philco-Ford, and Grumman. Two of the contractors performing that study, which ended in proposals for the design of the ground network and several types of user equipment (GPS receivers), would be chosen to create the designs. Then one of the two would be selected to actually implement Phase 1 of GPS.

After the first round down-select, we were now playing in the big leagues, GDE/Magnavox against Philco/TRW. The Philco leader, Jim Spilker, and our guru, Charlie Cahn, had to work together along with Rockwell engineers to define a common signal for GPS. The product of their work is still in use as it was defined then, at least for the civil C/A GPS signal. There were tradeoffs and compromises. The length of the short code was a contentious issue. TRW had built a 512-bit correlator, and Philco pushed that for the C/A-code. Cahn wanted 2048 bits to minimize inter-satellite signal interference. They compromised on 1024 bits. Charlie wanted a serially transmitted short code/long code for the military signal to enable long-code acquisition, a technique we had used in all our modems. But Spilker pushed for the codes to be transmitted in phase quadrature, a more elegant solution that prevailed. The need for a short code arose because the receiver could not acquire the long military signal unless it knew time to microseconds accuracy. The military code was very, very long. By first acquiring the short, repetitive C/A signal, the receiver could read its data and determine time close enough to make a long-code acquisition search practical.

The GDE/Magnavox team won the Phase 1 contract, and we were developing the first military and civil GPS user equipment (UE). Our Phase 1 UE contract included quantities of a 4-channel, high dynamics set for the F-4 fighter aircraft; a 2-channel aircraft set for the bigger and slower C-141 and helicopters; a manpack; and a civil aircraft set that looked like a TACAN and used only the C/A GPS signal. The three aircraft sets were called the X-set, Y-set and Z-set, respectively. Before long, Col. Brad Parkinson, director of the Joint Program Office, decided that there should also be a competitive high-dynamics set and another manpack, and awarded a contract to Texas Instruments. The USAF avionics laboratory wanted a piece of the GPS action so it awarded a what it called a “high technology” GPS UE contract to Rockwell Collins.

For various reasons, many not of its own making, Collins eventually became the number-one supplier of military GPS UE, long after Magnavox faded from the scene. (Hughes and then Raytheon eventually acquired the Magnavox GPS crew, where some of my former colleagues still work today.) The Collins unit flew in the C-141. Our X-set flew in a pod under the F-4. The complement of equipment, GPS receiver, navigation computer, power supply, and so on, was too big to be installed into the aircraft, so it was housed in the pod.

Building the Crew

To staff the contract required hiring many new engineers. We scoured our competitors and prior employers that had people experienced in the needed hardware and software disciplines, and were able to create a crew that went on to become major contributors to GPS developments for decades. Some started their own GPS companies, like Min Kao who, with Garry Burrel of King radio, later became the MIN and GAR in GARMIN. Another GPS company started by Magnavox people is CAST Navigation, a GPS simulator manufacturer.

The Magnavox Marine Division developed commercial Transit receiver and integrated shipboard navigation systems and survey systems. Later on, it pioneered GPS-based marine navigation systems and eventually split off into another company called Navcom, formed by Jim Litton, which later became part of John Deere. Several notable GPS experts from that Magnavox cadre like Tom Stansell, Ron Hatch (still with Navcom), and Jerry Knight are actively consulting today. So with all modesty, I have to say that I too was part of that original group who can claim some degree of fatherhood for GPS user equipment and receivers.

Over the next several years, I became an ambassador for GPS, traveling the world, particularly to visit potential military GPS users in NATO and at other allies. In the late 1970s, Magnavox and Collins were awarded the Phase 2 user-equipment developments. About a year before the production contract was awarded to Collins, I had left Magnavox to join Interstate Electronics (IEC), now a major part of L-3 Communications, to lead its efforts to become a military GPS user-equipment supplier. IEC had a unique technology for tracking submarine-launched ballistic missiles using a GPS translator tracking system. We succeeded in applying it to the DOD test ranges and for Trident missile tracking and submarine navigation. In my later years there, we eventually miniaturized the GPS receiver to the point where it could be applied to guiding missiles and projectiles.

After nine years at IEC, I decided to go out on my own as a consultant and formed Global Systems and Marketing, Inc. For the next 20 years I worked on various assignments from most of the major GPS companies and several small businesses that were trying to find a position in the GPS market. I also participated as an expert witness in many legal cases involving GPS, from patent disputes to accident reconstruction to parolee tracking.

Looking back now from the beginning of my retirement, I can obviously say I’ve learned a lot. Two things stick out in my mind:

  • Never believe the schedule and budget anyone offers up, because new developments will likely take longer and cost more than originally estimated;
  • When you stop being better, you stop being good.

I know the future holds more miraculous applications of GNSS technology because of all the brilliant, innovative people working in the field that I have met, and those that I haven’t met but have read about in places like GPS World. You are all very fortunate to be part of what I call the most important dual-use system (after the Internet) ever invented.

Len Jacobson is a retired GPS consultant, having worked in the field since 1968. He is still active in the Institute of Navigation, having been Western regional vice president twice and held leadership roles in several of its conferences. He lives in Long Beach, California. Visit his site at