Polaris and Transit
I don’t want any damn fool in this laboratory to save money, I only want him to save time. The final result is the only thing that counts, and the criterion is, does it work?
—Merle Tuve, speaking of the development of the proximity fuse as quoted by J. C. Boyce in New Weapons for Air Warfare.
hough Sputnik I was a shock to America, it also furnished the United States with the means to develop a technique that allowed the Polaris submarines to aim their nuclear missiles at Soviet cities with greater accuracy.
This is not what two junior physicists, Bill Guier and George Weif – fenbach, thought they would be doing when they went to their jobs at the Applied Physics Laboratory on the Monday after Sputnik was launched. They tuned into the satellite’s signal out of an interest more akin to Roger Harvey’s and Florence Hazeltine’s than to Fred Whipple’s or Bill Pickering’s. They had no research aims in mind.
Within days their attitudes changed as they tried to characterize the satellite’s orbit as precisely as possible.
Guier and Weiffenbach were among many scientists worldwide who were attempting to determine Sputnik’s orbit. All but Guier and Weiffen – bach calculated the orbit on the traditional basis of finding angles to the orbiting body. The Moonwatchers recorded what they saw through their telescopes; Minitrack allowed angular measurements to be calculated from radio interferometry; and the radar dish at Jodrell bank, which would normally have been trained on radio sources in the galaxy, swiveled to keep the satellite in its focus, thus giving direct angular measurements.
By contrast, Guier and Weiffenbach recorded the way that the radio frequency of the satellite’s transmitter appeared to change as it passed within range of the lab (the Doppler shift). Pickering’s committee at the IGY had considered and dismissed the possibility of calculating orbits from Doppler data, concluding that the results would not be accurate enough. Given the techniques of data analysis the IGY committee envisaged, this conclusion was correct. However, Guier and Weiffenbach were to develop an alternative interpretation of the Doppler data, one that was subtle and that relied heavily on new computational and statistical methods.
Those who break with tradition or with accepted modes of practice often provoke hostility, and Guier and Weiffenbach were no exception. Their methods were ridiculed twice: first when they calculated an orbit for Sputnik, and then when their method served as the basis for unraveling some of the secrets of the earth’s gravitational field.
Fortunately for them, not everyone was skeptical. Among those impressed by their work was their boss, Frank “Mack” McClure, who saw how their methods could provide the basis of a satellite navigational system that would serve the Polaris submarines. That system—Transit—also became the first civilian global satellite navigational system.
Before Transit, the only system of navigation effective worldwide was the one that had been available to Odysseus when he escaped from Calypso and “used his seamanship to keep his boat straight with the steering oar.” Odysseus navigated by the stars, keeping the Great Bear to his left and his “sleepless eyes” on the Pleiades.
During the next three thousand years, with the introduction of increasingly sophisticated mathematics, nautical almanacs, accurate clocks, compasses, and instruments to measure angles to the sun, moon, stars, and planets, celestial navigation grew in sophistication and precision. By 1975, when William Craft (who later became a commander and the director of seamanship and navigation at the U. S. Naval Academy in Annapolis) took sightings from the deck of his cruiser, he could determine with a high probability that his ship was within a given circle of radius two nautical miles. By then, says Craft, the practitioners of celestial navigation had become high priests of a secret sect, performing their rites at dawn, noon, and dusk. Though Craft’s methods were more elaborate than those of Homer’s description, the idea was the same as that which guided Odysseus home—to navigate by the stars.
If Homer had written his epic five hundred years later than he did, Odysseus would have known to calculate his north-south direction from readings of the sun’s altitude at noon. Two hundred years after that, by the second century B. C., Homer could, with some loss of poetry, have described Odysseus’s journey in terms of latitude and longitude, the system then suggested by Hipparchus for defining position on the earth’s surface. However, like mariners of later centuries, Odysseus would have been very unsure of his position when clouds obscured the skies.
Dead reckoning would have helped, particularly in the Mediterranean, where currents are light. Knowing the point of departure, the ship’s initial speed (estimated) and heading, mariners learned from the sixteenth century onwards to calculate a new position relative to their starting point. They estimated (by eye) the effects of wind and current. By repeating the process for every tack, that is, by adding velocities (the speed and direction of every tack), and plotting them on paper, they navigated to their destination, making estimated course corrections as they went. Much easier in the description than in practice.
As the journey progresses, the errors add up. If you are wrong in your first estimate of speed and position, clearly you will be even more wrong after the next tack. You might, of course, be lucky and have the errors cancel one another. But how would you know? In clear weather on calm seas, one of the high priests of celestial navigation could check the position estimated by dead reckoning against a position fixed with reference to the stars. By the 1950s, sextants fitted with infrared filters permitted readings through light cloud cover of the sun’s position at noon. Nevertheless, sightings were not always possible. Navigators have stories of many days passing during which they could not get a celestial fix. In that time dead reckoning could lead a ship far off course, making steering an optimum course across the oceans difficult and adding danger and cost to the journey.
In the second half of the twentieth century, radar improved navigation in coastal waters. Since the early 1980s, a system known as Omega has provided worldwide accuracies akin to those of celestial navigation, if one knows one’s position roughly to start with. But in 1957, when out of range of coastal radar, navigation still came down to dead reckoning and celestial navigation. Not a good system if for some reason you need to know your position as accurately as possible at any time of the day or night, fair weather or foul.
Yet an accurate position fix was exactly what the Polaris submarines would need should the order come to fire, and it was exactly what the submarines did not have. Thus the Polaris development, as a select few members of senior staff at the Applied Physics Laboratory knew, was vulnerable to critics both within the Navy and in other branches of the armed services.
Polaris carried intermediate-range ballistic missiles, capable of travelling 1,200 to 1,500 miles, and was part of the U. S.’s strategic triad of land – based and submarine missiles and long-range bombers. The submarines were deployed in the Arctic and were intended to deter the Soviet Union from launching its own nuclear missiles, the idea being that the United States would always have the capacity for massive retaliation, thus nullifying the traditional military benefits of a surprise attack. Amidst widespread and intended publicity, consistent with the Eisenhower administrations “New Look” strategy, the first Polaris missile was fired from the USS George Washington in July I960.
To achieve its aim, the Navy (specifically, the Special Projects Office of the Navy, later Strategic Systems Projects Office) needed to be certain that its missiles would land within a particular radial distance of the target.
The missiles followed ballistic trajectories. Like bullets from a gun, they were carried to their destination by momentum and gravity. Slight course corrections were possible during the ascent while the solid rockets fired, but these corrections were like those needed to steer down a particular road; they did not permit you to change roads. Accurate positioning and targeting were crucial for getting on the right road.
Although the submarines needed an accurate reckoning of their position, their strength was (and is) in their stealth, constantly moving underwater, prepared to fire at any time and to move away. As long as they remain underwater they are virtually undetectable, and their nuclear fuel permits them to stay submerged without refueling for many months. A force of such submarines is practically invulnerable to a first strike. In this scheme of things, sitting on the surface taking a position fix from the Sun, Moon and stars was not an option.
The Special Project Office’s initial solution was that Polaris would carry what was then the comparatively new technology of inertial navigation systems. These, effectively, are automated dead reckoners. They were originally mechanical and are now electronic. They compute from measured accelerations the actual course of a ship, submarine, or missile. They do not refer to anything outside themselves but measure the accelerations experienced in each of three dimensions on the parts they are constructed from. As such, if the errors can be kept to a minimum, they are ideal for submarines, which may be out of port for some time and rarely surface.
Like dead reckoning, though, inertial navigators accumulate errors. It is difficult to say what those early errors were in Polaris because the targeting and positioning errors of the system are still classified, even though the American Polaris submarines came out of service in the mid 1970s (the last of the British Polaris submarines was decommissioned in 1996). The errors were probably less than those of an inertial navigator on a surface ship, where waves would add to the measured accelerations.
Some of an inertial navigation system’s errors were a consequence of the difficulty of manufacturing the mechanical versions with sufficient precision. However, within the Polaris program, anything that money and expertise could have done to improve manufacturing techniques would have been done or attempted, because Polaris (and by extension Transit) carried the naval designation “Brickbat-01,” signifying that the project had a high procurement priority. If a computer was waiting to be shipped to someone else and a Brickbat-01 project needed it, the Brickbat-01 project got the computer.
Nevertheless, the accuracy of the inertial navigation system was not good enough. In one day, they accumulated errors that were far greater than those specified for Polaris’s positioning accuracy. Since the submarines were on station for months at a time, this was a problem. What was needed was an external reference system that minimized the submarines’ exposure; something that would correct inertial guidance errors in the same way that a celestial fix corrects errors in dead reckoning. Such a system was the raison d’etre for the Transit satellites and was made possible by the techniques developed by Guier and Weiffenbach.
Transit was important to the Department of Defense for two reasons: first, for navigation; second, because the satellite orbits revealed details of the earth’s gravitational field and thus the shape and structure of the earth and the relative positions between geographic locations. It was this second aspect of the Transit program that led at times to a high security classification. By learning about the gravitational field, military planners knew both the position of Moscow, say, with greater accuracy as well as which course to select to the target and what course corrections were needed, and they didn’t want anyone else to know how much they knew.
Given that the Polaris submarines were to be deployed in the Arctic, the best orbit for a navigation satellite was one passing over the poles. In this orbit, a satellite would be visible to the submarines every time the spacecraft passed over the north pole, once every ninety-six minutes for a four-hundred-mile-high orbit. From the beginning of 1964, there was always at least one operational Transit satellite aloft. Transit’s appeal was that it worked in any weather and the submarine need only approach the surface once at night and deploy its antenna for ten minutes at most. An important attribute of these antennas was their low radar profile, which was important because radars capable of detecting a periscope’s wake were then being developed. The system was passive, and thus the submarine did not need to broadcast a betraying signal in order to get a fix.
Within a few years, when more satellites had been launched, it was possible to get a position fix anywhere in the world at least once every three hours, sometimes as often as once every ninety minutes. For the first time ever, navigators could fix their position with greater accuracy than was possible with celestial navigation and could do so more frequently and in any weather.
The original Polaris system specification called for satellites that would locate position to within a tenth of a nautical mile, or about six hundred feet. APL’s scientists say this accuracy was available from December 1963, after the first operational satellite was launched. That accuracy improved by the mid 1980s to twenty-five feet. Accuracies of sixteen hundred feet were more typical for cheaper Transit receivers, while surveyors located position to within a few feet with observations of more than one
As a navigational aid at sea, Transit was a marked departure from the
past. First, it relied on frequency rather than angle measurements, and second, it made a psychological break with the long past of celestial navigation (radar navigation in coastal waters was also contributing to the change). Instead of wielding sextant, charts, and nautical almanacs, the navigator need only look at the value of latitude and longitude calculated by Transit’s shipboard computer from the signals transmitted by the satellite.
Once the Department of Defense made Transit available to civilians in 1967, oceanographers and offshore oil prospectors became the first to use the system, followed by merchant fleets and fishing vessels, and finally pleasure boats.
These developments—both technical and marketing—took some time. The U. S. Navy’s surface fleet did not make widespread use of the system until the late 1970s. Aircraft carriers were among the first to be equipped; on cruisers such as that on which Commander Craft served, Transit was installed later. Even when Transit was widely available, naval navigators continued to check its output with position fixes calculated by traditional methods.
The first experimental Transit went into orbit on April 13, 1960. Tom Stansill, an early Transit participant who later joined Magnavox, which manufactured receiving equipment, recalls that the very first receivers on Polaris submarines occupied four racks and cost (in today’s dollars) somewhere between $250,000 and $500,000. Typically a rack of electronics was six feet high, two feet wide, one and a half feet deep, and held more equipment than one man could lift. By the late 1960s, when sales opened to civilians, a receiver occupied about half a rack and cost between $50,000 and $70,000. There was a breakthrough in receiver technology in the mid 1970s, and the equipment came down in size and in price to $25,000 and has decreased steadily since then.
Now, of course, the Global Positioning System (GPS) of navigation satellites, which is available every minute of the day, has taken over from Transit. The last operational Transit satellite was scheduled to be switched off at the end of 1996. GPS is so accurate that it can detect the sag on an aircraft’s wing. Almost daily, it seems, another unconventional use is found for the system, one of the most recent being as an aid to golfers negotiating the perils of golf courses. Ships can carry electronic charts that GPS updates continuously, and the automation is opening the way to the controversial practice of ship bridges operated by one person. As with Transit, civilian users outnumber the military for whom it was intended, and GPS products are becoming major business opportunities.
Unlike Transit, GPS was designed to include aircraft navigation. To get an accurate position including altitude with Transit, two satellite passes were needed, with interpolation of these fixes by an inertial navigation unit. Transit was initially used in this manner by radar picket planes that remained in the air for many hours. However, a high-speed jet needs a much faster acquisition of navigational information. The great advantage of GPS for aircraft is that its radar imaging technique allows aircraft to get a three-dimensional fix without an inertial navigation unit.
But it was Transit that was the first to provide a worldwide, space- based system of navigation in any weather. And it was the Transit team that first encountered the unknowns of designing a navigational system for space.
The Applied Physics Laboratory, which masterminded the project, was well suited to the task. The lab started out in 1942 as an independent contractor for the Navy. It became part of the Johns Hopkins University after World War II, though the university was not initially keen to embrace a laboratory focusing on defense work.
Merle Tuve, one of the scientists who expressed most doubt about whether satellites should be a part of the IGY, was the laboratory’s first head. He had been an advisor to Robert Goddard and was an expert on the ionosphere. He was also among those eating the 21-layered chocolate cake at Van Allen’s home in 1950.
Tuve’s watchwords as head of the lab during wartime were those at the front of this chapter. To some extent, that ethos still pervaded APL in the mid to late 1950s. One of APL’s most important wartime developments for the Navy—a proximity fuze—proved valuable for Transit’s development. The fuze was a significant advance for surface-to-air artillery, because it detonated a shell when it was closest to the target rather than on impact, thus increasing the artillery’s effectiveness. The development was prompted by the difficulty the Allies had in hitting fast moving aircraft and the Vis and V2s.
More than a decade later when Guier and Weiffenbach decided to determine Sputnik’s orbit, they turned first to concepts underlying proximity fuses. And when the Transit development began, the skill acquired by engineers building vacuum circuits for artillery proved, Weiffenbach says, invaluable in building components able to withstand launches.
In 1947, APL formed a research center to work on problems in basic research uncovered during the war years. Many of these were centered on aspects of the upper atmosphere that might affect missiles, and the lab was given some of the captured V2s for its work. In tandem with Princeton University, APL became one of the member institutions of the Upper Atmosphere Research Panel, and James Van Allen was the lab’s representative until he left to concentrate on basic rather than military research.
After the war, two men joined APL who were to play an important role in the conception and development of Transit. They were Frank McClure and Richard Kershner. Like Ralph Gibson, who would become head of APL, they came from the Allegany Ballistics Laboratory. McClure, who was to have the idea for Transit, became the research center’s first head in 1947. Kershner would become the deeply respected team leader who brought the Transit system to fruition.
In early October 1957, when Guier and WeifFenbach tuned in to Sputnik, McClure was spending half of his time at the Navy’s Special Projects Office. Kershner, too, worked with Special Projects and was later made responsible for APL’s consultative services to Special Projects. Both McClure and Kershner had a close relationship with Captain (later Rear Admiral) Levering Smith, then the deputy technical director of Special Projects. McClure was thus ideally placed to know of Polaris’s need for improved position fixing.
By 1957, Gibson had become head of the lab. Having been sounded out as a potential director of Defense Research and Engineering, he was well placed politically to further plans for a navigation satellite. Gibson had not wanted the job, which was the number three civilian position at the Pentagon, but he clearly had influence and contacts which doubtless were exercised in favor of Transit.
Transit was to encompass a truly formidable array of physics (most branches, including, eventually, quantum mechanics), mathematics, computing and technology. Often the whole Transit system was being designed in the expectation, maybe even blind faith, that when needed, the required new technologies (transistors, battery technology, solar cells, etc) would be in place. It was an approach with which Kershner and Levering Smith were comfortable, and which, in the end, proved successful. For more than thirty years Transit satellites have been in orbit. Now, as the twentieth century closes, GPS has taken over.
It is still only 1957.
It is the Monday after the Friday (October 4) when Sergei Korolev watched Sputnik ascend. Korolev is preparing Sputnik II. Fred Whipple’s orbital determination programs are being debugged. John Mengel is supervising frantic modifications to the Minitrack stations. The police will soon catch Roger Harvey speeding. Bill Pickering has returned to the Jet Propulsion Laboratory, where he is plotting deeply with Wernher von Braun. There is no such thing as Transit. Not even a whisper, nor will there be for another five and a half months. First, there are some important steps to be taken.