Charting a Course Toward Global Navigation

An early rendition of the Navstar/GPS constellation showing 18 satellites in orbit.

Charting a Course Toward Global Navigation

Steven R. Strom

In the 1960s, the Global Positioning System emerged as a radical new way to provide precise navigation for U.S. armed forces across the globe. Early work at The Aerospace Corporation helped get the program off the ground.

The recent conflict in Afghanistan has once more focused attention on the remarkable capabilities of the Global Positioning System (GPS), a satellite-based navigation system that allows users to pinpoint their location anywhere in the world. GPS first received widespread publicity during the Persian Gulf War of 1991. Though not fully operational at the time, the system had a significant impact on military operations, enabling allied forces to coordinate their movements in the featureless Iraqi desert and achieve a rapid victory with a minimum of casualties. Just over a decade later, GPS was used with similar success in the war in Afghanistan, a country renowned for its difficult terrain. Although the development of GPS can be traced back to the military demands of the Cold War era, it has gone far beyond its initial defense applications and now extends into the daily lives of millions of civilians, who use it for commercial, recreational, and educational purposes.

As the first president of Aerospace, Ivan Getting oversaw the development of Project 621B, the precursor to the Global Positioning System.

Many people are unaware that this revolutionary advance in navigational science was conceived, in part, through studies conducted at The Aerospace Corporation in the early 1960s. In addition, two of the men most responsible for its success have direct ties to Aerospace: Ivan Getting, the foremost initial advocate for GPS, was the corporation's founding president, and Bradford Parkinson, who headed the first GPS Joint Program Office, is chair of The Aerospace Corporation board of trustees. During the first half of the 20th century, researchers at various organizations were separately developing the technologies that would eventually be used to create GPS. By 1960, much of this work had coalesced in a manner that would place Aerospace at the heart of GPS research.

Precursors

Radio was the first modern technology applied to position finding. As early as 1912, Reginald Fessenden began conducting experiments on the coast of Massachusetts and devised a simple system of using radio waves to help ships determine their positions. The system was extremely inaccurate and geographically limited. The development of the first true all-weather position-finding system, LORAN A (Long Range Aid to Navigation), had to wait until World War II, when the destruction of Allied ships in the North Atlantic gave rise to a crash program to create such a system. LORAN A was developed in Division Eleven of MIT's Radiation Laboratory. Coincidentally, in October 1940, a 28-year-old research physicist named Ivan Getting was beginning his tenure as head of Division Eight of the Radiation Laboratory. Although Getting's division did not do any work in navigation, as a member of the Radiation Laboratory Steering Division he "was very much aware of the remarkable success of LORAN." The Navstar/GPS system would later employ LORAN's method of using time difference in the arrival of radio signals to calculate position. During the postwar period, variations of LORAN A were developed, including the more accurate, high-frequency LORAN C and the low-frequency OMEGA system.

Brad Parkinson served as the first program manager of the GPS Joint Program Office, established in 1973.

Many of the major scientific and technological advances of the mid-20th century were closely linked to the launching of the first artificial satellites. Indeed, the development of satellite technology was a crucial precursor for GPS, and the system's key navigational concept was discovered as a result of the Sputnik launch on October 4, 1957. Sputnik was little more than an orbiting radio transmitter, but it captured the attention of scientists across the globe. Two scientists at the Johns Hopkins University Applied Physics Laboratory (APL), George Wieffenbach and William Guier, realized as they listened to Sputnik's signal that they could determine its orbit from the Doppler frequency shift detected as it passed overhead. Their measurements were subsequently confirmed by findings from other tracking sites. From this observation, Frank T. McClure at APL reasoned that, conversely, if the orbit of a satellite were known, then Doppler-shift measurements could also be used to determine any ground position on Earth.

Pursuing this concept further, the Navy initiated studies for its first satellite navigation program, the two-dimensional Transit system, in 1958. Many scientists, engineers, and military leaders recognized from the beginning of the space race that satellites held great potential for navigation. In 1959, concurrent with the development of the Transit program, a staff report to the House Select Committee on Astronautics and Space Exploration predicted that during the next decade, "Satellites can, and will, become one of the principal aids to navigation for sea, air, and perhaps, space craft." The first Transit prototype satellite was launched in April 1960, demonstrating the feasibility of a satellite-based navigational guidance system. The development of Transit was important for the future of GPS, as elements of the program were eventually incorporated into the GPS architecture.

Engineers from Aerospace and Grumman in 1972, testing a transmitter for the 621B Defense Navigation Satellite system at White Sands Missile Range, New Mexico.

Another system used in early GPS studies was MOSAIC, a three-dimensional LORAN-type ballistic missile guidance system developed in the 1950s by the Missile Division of Raytheon, where Getting had gone to work in 1951 as vice president of engineering and research. MOSAIC (Mobile System for Accurate ICBM Control) was first proposed to the Air Force by Getting and his colleague Shep Arkin on May 11, 1960. The Air Force was worried about the potential vulnerability of America's land-based ICBMs, so the MOSAIC plan was to mount the Minuteman missiles on railroad cars and rotate their positions. In addition, MOSAIC provided for advanced control and guidance systems once the missiles were in flight. Just six weeks after Getting presented the MOSAIC proposal to the Air Force, he was invited to become the first president of the newly formed Aerospace Corporation. Getting's presidency began on August 1, 1960.

Project 621B

Only a few months after the formation of Aerospace in the summer of 1960, much of the knowledge base that was pivotal to the development of GPS was already taking shape. By necessity, Getting began his tenure with a rapid hiring campaign, attracting a large block of researchers and engineers from Space Technology Laboratories (STL). Several of the planners at STL had been briefed on the MOSAIC program, and although it was canceled in early 1961, they brought their expertise and knowledge to Aerospace. The principal mission of Aerospace was "to aid the United States Air Force in applying the full resources of modern science and technology to the problem of achieving those continuing advances in ballistic missiles and military space systems which are basic to national security." To that end, Aerospace initiated a series of studies in areas where the application of space systems might prove most valuable. One of the earliest of these studies dealt with navigation.

An artist's rendering of a Navstar/GPS satellite.

By the beginning of 1963, Aerospace had some 1463 scientists and engineers on staff. Two major studies were initiated that year. Project 75 attempted to define ballistic missile systems for the year 1975. Project 57 (the name was derived simply by inverting the numbers of Project 75) sought to clarify the areas where space systems could be successfully used for military applications. The Project 57 study was directed by Phillip Diamond of the Systems Planning Division, and, as Getting noted, it was "in this study that the GPS concept was born." In 1963, the Space Division of the Air Force began supporting this study, known as Project 621B, and requested that Aerospace continue its work on determining navigation coordinates from satellite signals.

The Air Force placed a high priority on finding a better positioning system for its aircraft. The Transit system was too slow and too intermittent to keep up with the high speeds of airplanes, and the Air Force hoped to obtain an accuracy of 15 meters—much better than what Transit was providing for ships. According to Parkinson, Project 621B had "many of the attributes that you now see in GPS. It has probably never been given its due credit." Getting relates that the Aerospace navigation studies were "directed at meeting the Air Force requirements as we understood them: the system should be responsive to an unlimited number of users; the user equipment was to be passive (i.e., nonradiating); and it was to be as accurate as technology would permit."

From 1964 to 1966, several Aerospace team members made outstanding contributions to GPS studies within Diamond's division. These men included Peter W. Soule, James B. Woodford, Alfred Bogen, Richard Dutcher, Howard F. Marx, and Hideyoshi Nakamura. It was Nakamura and some of his coworkers who suggested that range measurements for an aircraft should be calculated using signals from four satellites. The aircraft's crewmembers could then obtain a three-dimensional position by measuring four distinct differences in the signals' arrival times and then adding these to a clock connected to a quartz oscillator. Each satellite would also have its own clock, which would be updated continuously by ground signals. In essence, this was the operational concept that eventually led to GPS as it is known today. Woodford, who had joined the 621B team in 1965, conducted research on the characteristics of the signals that were transmitted from satellites to receivers. Following the conclusion of these studies in 1966 and briefings by Soule, Nakamura and Woodford, the Air Force awarded contracts to TRW Systems and Hughes Aircraft Company in 1968 to begin design studies for the proposed system. Diamond and his team, now including Walter C. Melton, Lawrence L Hagerman, and Frank Butterfield, assisted with the design studies and continued research on other facets of GPS, including satellite deployment and the placement of onboard atomic clocks.

B. P. (Pete) Leonard wears a Navstar backpack in this 1978 photo. Leonard, then vice president of Aerospace's Navstar program group, is flanked by Col. Don Henderson (left) of the Space and Missile Systems Organization (SAMSO) Navstar program office and Ed Lassiter (right), principal director of Aerospace's Satellite Navigation Systems Directorate.

The ultimate implementation of GPS would not have been possible without concurrent advances in other fields. The 1960s witnessed remarkable leaps in the development of computers, solid-state microprocessors, atomic clocks, signal processing, and bandwidth utilization techniques. The advances in atomic clocks allowed Roger Easton of the Naval Research Laboratory's (NRL) Naval Center for Space Technology to develop an innovative satellite-based time-transfer concept known as Timation (Time Navigation). Timation was conceived in 1964, and the first Timation satellite was launched in 1967, with a second following in 1969. These satellites each carried a high-quality crystal oscillator. The third satellite, launched in July 1974, was the first to fly an atomic clock. Meanwhile, Aerospace continued to conduct its own research for the 621B program. This included a successful experimental flight test program led by Walt Melton at White Sands Missile Range that used pseudorandom noise breadboard receivers, three ground-based pseudolites, and another in a tethered balloon. By the early 1970s, Aerospace recommended a concept design that employed 20 satellites placed in geosynchronous inclined orbits ranging 30 degrees north and south of the equator.

Compromise and Consensus

By this time, Getting and Diamond were actively working to obtain the full backing of the Department of Defense (DOD) for GPS. Air Force support for 621B continued, but any full-scale GPS effort would need support from DOD. It was becoming increasingly clear that some type of coordination was needed among the three competing ideas for a fully developed satellite-based navigation system: APL's Transit, NRL's Timation, and the Air Force's 621B. To coordinate these efforts, members of the Navy, Army, and Air Force formed NAVSEG (Navigation Satellite Executive Group) in 1968, but the committee had no real powers to enforce any decisions that it reached. In 1969, Getting asked President Nixon's science advisor, Lee Du Bridge, for help. Du Bridge had been Getting's boss at the MIT Radiation Laboratory. He advised Getting not to advocate a presidential commission to sell GPS, but to push his ideas through the military customers with the greatest needs for a navigation system. From that time on, Getting concentrated his efforts on the Air Force and the scientific elements of the Defense Department.

In November 1972, Air Force Col. Bradford Parkinson was assigned by Gen. Ken Schultz to manage the satellite navigation program. Parkinson's move from the Advanced Ballistic Missile Reentry System program to 621B marked the beginning of the first real progress in the eventual approval of GPS because he quickly realized that a synthesis of the three competing proposals would be necessary. Parkinson remembers that "I entered the picture when those three concepts were in a death struggle—none of them was going anywhere." Parkinson examined the competing concepts in great detail and came to the conclusion that some elements of all three systems would be needed in GPS if it was to prove successful.

Weight and balance tests of the third prototype satellite in the Navstar/GPS constellation are conducted prior to its launch from Vandenberg Air Force Base.

On April 17, 1973, DOD authorized the creation of a joint, three-service program office and selected the Air Force as the lead military service. Parkinson was appointed to be the first program manager of the newly created GPS Joint Program Office. The program's headquarters were located at the Los Angeles Air Force Station (as it was then known), the headquarters of the Space and Missile Systems Organization (SAMSO) in El Segundo, California. The Los Angeles Air Force Station was adjacent to The Aerospace Corporation, which established a GPS program office in July 1973 with Bruce L. Adams as its manager. He was succeeded by Edward Lassiter in 1974.

In August, Parkinson presented the 621B proposal to the Defense System Acquisition Review Council (DSARC), which promptly rejected it. But the council expressed likely support if the proposal could be expanded to address some of the ideas and requirements of the other armed services. Over the Labor Day weekend in 1973, Parkinson convened a meeting of about 12 military officers at the Pentagon to discuss such a multiservice system. It was at this meeting, he said, that "the real synthesis that became GPS was created." With program approval from Malcolm Currie in DOD Research and Engineering, Parkinson was able to convince all parties that the synthesized design was the proper one to select. The compromise system used atomic clocks in its satellites and orbits similar to those used for the Timation system, but with higher altitudes to provide a 12-hour period. The structure and frequencies of the digital signals were essentially the same as those used in 621B. The number of satellites proposed for the 1973 GPS system, 24, is the number in use today. As Parkinson would remark, "Basically our Labor Day system is still the current system."

Models of different versions of GPS in 1991.

As the program manager, Parkinson now had a unified development team for the hard work ahead, and with his new compromise in hand, he went back to DSARC and was granted approval to proceed with GPS work on December 22, 1973. Initial funding was about $150 million. The program was also renamed Navstar (which is not an acronym), but people still referred to it as Navstar/GPS, or simply GPS.

The ability to create the synthesis that became GPS and build the system remains Parkinson's outstanding achievement as program manager. As Getting would later remark in his autobiography, "The approval of the joint project, which became known as Navstar, would probably not have come about ... had not General Schultz, commander of the Space Division, assigned Col. Brad Parkinson as program manager in November 1972."

Rapid Development

Over the next 15 years, GPS development proceeded at a rapid pace. Much of the work in Phase I (concept validation) consisted of testing the many potential types of user equipment. Many of these experiments occurred at the Yuma Proving Ground in Arizona using ground-based transmitters in lieu of orbiting satellites. Extensive testing was also done with the position determination of a wide variety of vehicles, aircraft, and troops with GPS receivers. Between 1977 and 1979, more than 700 tests were conducted, and all of them confirmed the system's extraordinary accuracy. On February 22, 1978, the first Block I developmental Navstar/GPS satellite was launched from Vandenberg Air Force Base, using an Atlas F booster. Three more satellites were launched in 1978. Ed Lassiter remembers that "Aerospace had a huge impact on the success of these first four launches and on the entire GPS program."

GPS Block II

The DOD approved Phase II of the program in 1979, the same year that Allan Boardman took over from Lassiter as GPS program director at Aerospace. This phase of GPS was intended to provide global two-dimensional coverage for a select group of users. In 1981, Jim Henry succeeded Boardman as principal director, and he remained in that position until 1992. Additional GPS satellites were launched in the early 1980s.

In 1985, Phase III (the production and development phase) began, and the first operational GPS Block II satellite was launched in February 1989. GPS was unexpectedly able to validate its worth following the Iraqi invasion of Kuwait in 1990, when the system provided invaluable navigational information to airborne, ground, and naval units of the allied forces. During and after the Persian Gulf War, the media's coverage of GPS helped stimulate a surge of civilian interest. By the time GPS was declared fully operational in 1995, its future success was virtually guaranteed.

Conclusion

In 1992, as a member of the GPS team, Aerospace shared the nation's most prestigious aeronautical award, the Collier Trophy. The citation accompanying the award called GPS "the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago." The award was a capstone to three decades of difficult development work, remarkable innovation, and tireless advocacy by Aerospace personnel, often at a time when only a handful of people recognized the system's enormous potential. As Getting would later note, "While the Collier Trophy was specifically directed at the GPS with principal recognition of The Aerospace Corporation, the Air Force, the Navy, and the associated contractor team, I look upon it as a recognition of Aerospace and all its programs and people."

The Collier Trophy