A widespread myth is that worldwide time synchronization was an unexpected consequence of GPS. “Certainly there was no serious consideration given to GPS becoming the de facto world standard for time ,” blogged Don Jewell in January 2008.28 Jewell spent more than thirty years in the Air Force and writes for GPS World. A 2009 dissertation posited that, “somewhat unexpectedly, the precise timing information transmitted by GPS satellites was quickly incorporated into many inventive applications that are not related to navigation. ”29 On the contrary, both Roy Anderson and Roger Easton anticipated worldwide clock synchronization. Anderson wrote in 1964 that his system would provide worldwide synchronization to approximately one microsecond.30 Easton wrote in 1967 that “possible fallouts from such a system are worldwide time synchronized to better than 0.1 microsecond. ”31 Thus the timing was more accurate by a factor of ten. In the Timation Development Plan, published in 1971, the estimated time transfer accuracy was improved again by a factor of ten, to better than 0.01 microsecond. Easton stated in 1974 that “precise orbiting clocks will prove to be a valuable tool in a variety of applications, by providing the entire planet earth with a single, accurate time system, enveloping the globe in a web of synchronized satellite signals. ”32 This was about fifteen years before the term World Wide Web was coined. These satellite navigation proposals provided three-dimensional position and time. Even though time was less prominent than positioning, it was extremely important. Today, space-based navigation systems are often referred to as providing PNT, which means positioning, navigation, and timing. Time-transfer experiments via satellite began with the Timation I satellite in early 1968. Timation II performed the first international time transfer in July 1972 between the Royal Greenwich Observatory, England, and the Department of Defense Master Clock at the U.S. Naval Observatory in Washington DC.33
By the critical year of 1973, when the initial GPS system was configured, the proposed Timation configuration was twenty-seven satellites in three planes, in eight-hour circular orbits, with ground stations in the United States or secure U.S. territories.
The differences between the rival services’ navigation proposals reflected their different needs. The Navy had a worldwide fleet, which included surface ships, submarines, and aircraft carriers. A worldwide three-dimensional system was important to meet the Navy’s needs. The Air Force wanted to be able to put five missiles in the same hole. A worldwide system was not as critical a requirement for the Air Force.
The Air Force and its private research arm, the Aerospace Corporation, developed a space-based navigation system called Project 621B. Some sources assert that it started in 1963; however, a 1966 briefing report (declassified in 1979) by Aerospace engineers J. B. Woodford and H. Nakamura includes a chronology that dates “SSD/Aerospace identification of potential need for a new navigation satellite ” to June 1, 1964.34 The date is probably an approximation. The study envisioned regional constellations of geosynchronous or near-geosynchronous satellites and characterized putting atomic clocks in the satellites as a “growth item. ”35 A paper presented by Woodford and two other engineers from Aerospace at the 1969 EASCON (Electronics and Aerospace Systems Convention) proposed three or four regional constellations around the globe, each with one satellite in geosynchronous orbit and three or four satellites in inclined elliptical orbits.36
The other 1960s range measurement system was the Army’s SECOR, short for sequential correlation of range. SECOR satellites used transponders to return radio signals sent from three ground stations at known, surveyed positions to compute the position of a station at an unknown position.37 It was designed primarily for geodetic purposes.
Toward the latter half of the 1960s there was pressure to consolidate space-based navigation system efforts and produce a system with three-dimensional capability that would be available worldwide and around the clock. Finding agreement on the design and deployment of a single shared system produced what Washington does best—multilayered committees, subtle infighting, budget wrangling, secret meetings, and afterward, differing accounts of what was accomplished and who should get credit.
4
One System, Two Narratives
Recollections and Documents
There are three stages of scientific discovery: first people deny it is true; then they deny it is important; finally they credit the wrong person.
Widely attributed to Alexander von Humboldt
Arguments about priority in inventing GPS are vigorous. Sorting them out is challenging due to the loss or unavailability of important documents and the effect of time on memory. Fortunately, they have not led to murder, unlike this tragicomic story: “John Glendon of St. Clement-Danes, Gent. was tried for the Murther of Rupert Kempthorne, Gent. on the 28th of October last, giving him a mortal wound near the Navel, of the depth of 10 Inches, of which wound he died the next day. The Evidence in general deposed, That the Prisoner and Mr. Kempthorne were at the Ship-Tavern at Temple-Bar, and some difference arose between them about Latitude and Longitude; Mr. Kempthorne alledging that there was no such word as Longitude. ”1
A Tale of Two Systems
The modern version of this argument concerns the importance of Timation, developed at the Naval Research Laboratory under the direction of Roger Easton, to the emergence and success of GPS. Some accounts of GPS history dismiss Timation entirely or sweep it aside as simply an effort to upgrade Transit, the Navy’s first navigation satellite system.2 That viewpoint traces the GPS lineage directly back to Project 621B, the navigation satellite program developed by the Aerospace Corporation, a federally funded research and development center sponsored by the Air Force.
Because the Pentagon appointed the Air Force as the executive service for GPS in 1973, and it has performed that role for decades, it is understandable that many assume GPS has always been entirely an Air Force program. Few people knew details about Timation during its development because it was a classified program, and its role became obscured once the NAVSTAR GPS program subsumed it. However, a reasonable examination of the individual characteristics of Timation and Project 621B, of the steps the government took to merge the two approaches, and of the resulting system, leads to the conclusion that GPS resembles the Timation approach more closely than that of Project 621B. The evidence that follows is not an attempt to discredit the contributions that Air Force managers, Aerospace Corporation scientists, or numerous private contractors made to the development of GPS. Rather, it attempts to present a balanced story, to promote wider appreciation for the contributions Timation made to GPS, and to accurately portray how GPS came to be the wildly successful program it is today.
Joint programs among the military services have always proved challenging and have sometimes failed. The F-111 fighter-bomber is an example of unsuccessful joint development of technology. Secretary of Defense Robert McNamara ordered the Navy and Air Force to develop the F-111 together. The Navy, judging the plane unsuited to carrier operations, was dissatisfied with its version, and the attempt to design an aircraft for both the Air Force and the Navy failed.3
As discussed in the previous chapter, various space-based navigation systems were proposed in the 1960s. The problems U.S. pilots had in the late 1960s and early 1970s destroying North Vietnamese bridges highlighted the need for precision munitions. But Vietnam War–era military budgets were stressed, so coordination between the military branches was encouraged. While the Pentagon had logical reasons to pursue a single, all-purpose satellite navigation system, differing needs among the services made joint development difficult.
Fig. 4.1. Timation Development Plan, 1971. The plan remained secret until the Navy declassified it in 1988. (Courtesy Naval Research Laboratory)
The Department of Defense established the Navigation Satellite Executive Steering Group, or NAVSEG, in 1968. It was a tri-service group with the title of chairman rotating annually among the services. Harry Sonnemann was special assistant for electronics in the Office of the Assistant Secretary of the Navy (Resea
rch and Development) from 1968 to 1976. He was a member of NAVSEG from its founding to its dissolution and was its chairman from 1969 to 1970 and from 1972 to 1973. He states, “The Special Assistants responsible for oversight of Communications and Navigation Systems in the Offices of the Assistant Secretaries (R&D) of the Army, Navy including the Marine Corps, and Air Force, served as the Senior Members of … NAVSEG. ”4 The Joint Chiefs of Staff established joint service requirements for a new space-based navigation system, including the ability for users to precisely position themselves in three dimensions and to precisely determine their velocity continuously, worldwide.5NAVSEG examined the services’ different design schemes, which varied in the number of satellites, their altitudes above the earth, and their orbital inclinations (angle compared to the equator); the types of radio signals used; and the methods of controlling the satellites from the ground.
The 1969 Electronics and Aerospace Systems Conference mentioned earlier featured three papers advocating low-, medium-, and high-altitude satellite navigation systems. Three Aerospace Corporation engineers, J. B. Woodford, W. C. Melton, and R. L. Dutcher, delivered the paper “Satellite Systems for Navigation Using 24-Hour Orbits. ” Their preferred constellation—the one used for Project 621B—had one satellite in a synchronous equatorial orbit and three or four satellites in inclined elliptical orbits. Three or four such constellations could provide nearly global coverage. A master ground station and two or more calibration stations continuously tracked and sent time and position information to the satellites, which then retransmitted signals to the receiver. The system required the ground stations to be in the same area as the satellite constellations, since the synchronous satellite remains relatively stationary over a point on the earth. This was a major weakness for military applications. For example, the European constellation required ground stations in that area. A wag working on Timation in the 1970s commented that the 621B European constellation would have required its ground station to be in Moscow.6 During a war, these stations would have been prime targets for direct attack or jamming the uplinks. A 621B satellite constellation could also have been destroyed by a single atomic bomb in space and the European constellation would have been denounced by the Soviets as a spy platform.7 Even if the 621B satellites had atomic clocks, the system was more vulnerable than Timation since only ground stations in the same area could update the satellite clocks in synchronous orbits.
Roger Easton, in his EASCON paper “Mid-Altitude Navigation Satellites ,” stated, “After considering both lower and higher altitudes the mid-altitude (approximately one earth’s diameter) polar circular satellite constellation has been selected as a prime possibility for an accurate, all weather, always available, three dimension, U.S. based navigation system. ” Later in the paper he stated, “The minimum number of satellites necessary to have three visible [from] anywhere on the earth’s surface is approximately twelve. ” He then added that more satellites were desirable since while having three in sight is enough for navigation, a fourth is occasionally required to correct the receiver’s clock.
Air Force Space Command senior historian Rick Sturdevant has written, “As early as 1969–1970, Aerospace Corporation president and GPS pioneer Ivan Getting had suggested to Lee DuBridge, President Richard Nixon’s science advisor, that a presidential commission be created to review how satellite navigation ought to proceed, because there were so many potential users. After thinking about it for several weeks, DuBridge concluded that execution of Getting’s proposal would be too difficult. He told Getting, ‘there are too many people, too many bureaucracies, too much politics, and too many agencies involved. Why don’t you just have the Air Force develop it the way we always did?’ ”8
Sonnemann comments, “It was our responsibility to arrive at a consensus with regard to the elements of the system, including the orbits of the satellites, the signal structure best suited for the project etc., etc., as well as management issues. ”9 This was challenging due to the different objectives of the services. The Air Force focused on precision targeting of munitions, whereas the Navy needed worldwide navigation for its ships, including missile submarines near the North Pole, and for airplanes based on aircraft carriers.
NRL’S Ron Beard, who was the second successor to Easton as branch head, has written that “from 1968 through 1970 the Timation concept grew from a Category 6.2 exploratory development project into navigation satellite techniques to a Category 6.3 development system concept. ”10 One requirement for a Category 6.3 program was writing a development plan. Consequently, the assertion sometimes made that Timation was just a study plan is incorrect.11 The March 1971 Timation Development Plan states, “The satellites provide the necessary data for the navigator to determine his latitude, longitude, altitude, and time. Not all navigators need to determine all these parameters. The user with the most stringent requirements will use four satellites in view and the equipment to receive signals from all four satellites; reduced requirements will result in one or more of the four signals being ignored by user’s equipment. This system was configured within the JCS [Joint Chiefs of Staff] navigation accuracy requirements. ”12
Figure 4.2, from the same page of the plan, shows an airplane receiving signals from four satellites. This illustrates the most stringent requirement of three-dimensional position and time transfer. This is one of many primary source documents that refute the myth that Timation was a two-dimensional system that required an atomic clock in the receiver. Some people continue to assert the myth today.13
NRL’S James Buisson, a physicist, and Thomas McCaskill, a mathematician, studied the optimal Timation configurations for the number of orbital planes, number of satellites, and orbital altitude. An important consideration was the placement of ground stations. For security purposes, the plan was to locate them only in the United Sates or secure U.S territories. Easton commented, “NRL found that the critical item in a satellite navigational system for unbelievable accuracies is the ground station location. The ground station location surprisingly determines the next item, the satellite constellation. ”14 As mentioned earlier, a problem with Project 621B was its European constellation ground station. The U.S.-based restriction on Timation ground stations created a gap in the Indian Ocean where no station was available to update the satellites. A problem the people developing Timation faced was uncertainty about when atomic clocks would be developed that were sufficient to replace crystal oscillators (quartz clocks) in navigation satellites.15 Timation I and II had crystal oscillators, and Timation III, scheduled to be launched in 1974, carried them in addition to two experimental rubidium atomic clocks made by the German company Efratom. Midaltitude satellite orbits, as is true for all orbits up to geosynchronous altitude, have the trade-off that higher altitudes give greater coverage whereas satellites at lower altitudes orbit more rapidly, permitting more frequent ground station updates. The June 1972 constellation study by Buisson and McCaskill proposed a three-by-nine constellation (three orbital planes with nine satellites each) at eight-hour orbits with evenly spaced planes.
Fig. 4.2. Illustration of an airplane using Timation signals. This sketch from page 10 of the Timation Development Plan shows users on land, at sea, and in the air. The system was configured to provide position (three dimensions) and velocity accuracy to within fifty feet for strategic and tactical aircraft, when using four satellites. (Courtesy Naval Research Laboratory)
In April 1973 Deputy Secretary of Defense William P. Clements issued a memorandum creating the Defense Navigation Satellite Development Plan (DNSDP), a joint Army, Navy, Marine Corps, and Air Force program. He designated the Air Force as the executive service and directed it to assign a program manager and establish a joint program office (JPO). He listed the following guidelines for the program. Clements directed the Air Force to deploy during 1977 a constellation of four synchronous repeater navigation experimental satellites (NES). This was a 621B constellation. He directed the Navy to launch in 1974 the medium-altitude Navigation T
echnology Satellite #1 (renamed NTS-1; this was the satellite formerly designated Timation III). The secretary’s memo requested a decision coordinating paper, a formal system design plan, by August 1973.
Navy captain David C. Holmes, a friend of John Glenn’s, joined the Naval Research Laboratory in early 1973 as a consultant working on Space Surveillance and Timation. His important role in developing GPS has been largely ignored. A humorous story Holmes told gives one the sense of NRL’S ethos:
They tell a great story about Dr. [A. Hoyt] Taylor [an electrical engineer who made important contributions to the development of radar] back in the early days of World War II. There was a rule at the laboratory that if you were the last person out of the laboratory you had to sweep up, and this applied to everybody. Dr. Taylor was sweeping up the laboratory one night in the early days of World War II when a young fellow came in… . He went in and saw this fellow sweeping out the place and asked him what kind of projects were done there. Then Dr. Taylor started telling him about the interferometers and various radar devices and things like that. He spent quite a bit of time explaining all these things. The young man went out talking to himself and saying, as he told the story later, “I certainly can’t contribute to a place like that. Even the janitor knows more than I’ll ever learn! ” The young man’s name was Arthur Godfrey [who later became a prominent radio and television broadcaster].16
GPS Declassified Page 8
