The Cesium-beam Clock
Dubbed the "flying clock" because it was flown around the world to check worldwide time standards, the atomic clock, based on cesium-beam frequency standards, was designed to maintain accuracy for 3000 years with only one second of error. In 1991, a new version with Cesium II technology was called the world's most precise commercially available time-keeping device. It maintains time consistently to one second in 1.6 million years. Atomic clocks are valuable in time-critical applications such as the space shuttle, airplane collision avoidance systems and telecommunications.
Today, ultimate timing accuracy is determined by the Global Positioning System (GPS), composed of ground reference stations and a constellation of satellites. All of the frequency standards at the individual ground reference sites are HP cesium-beam standards. Many other sites worldwide monitor GPS and virtually all of these use HP cesium standard models.
AICS Research's Text
Navy Navigation Satellite System
The picture above is Guam in the summer of 1964. The van on the left is completely filled with Hewlett-Packard instruments, including an HP clock. The van is so filled that there is room for only one small stool to sit on while you reach in front and behind you to track satellites.
The van on the right was a bit emptier. It was a radio teletype (RTTY) van, built by Collins Radio (now Rockwell), of Cedar Rapids, Iowa. RTTY communications allowed us to establish an early world-wide internet of sorts in the 1960's, where we could all talk to one another, anywhere in the world, relaying messages printed out onto paper tape.
But the far more important van was the one on the left, which in this case was specifically assembled by three friends and myself in New Mexico. Indeed, we assembled three of these vans before we took this one to Guam. These vans were air-transportable (helicopter liftable) to allow us to go anywhere in the world. And over the next several years, 300 close friends and I did travel the world with these vans as a method of earning our way through school.
Although you can't see them in this photograph, the van on the left was filled with HP instruments -- including an HP temperature-stabilized quartz clock. In 1965 and 1966, many of these clocks were exchanged with the new HP cesium beam clocks. The HP clocks allowed every van, anywhere on the surface of the earth, to be synchronized within 10 microseconds of one another.
Maintaining extremely accurate time is essential to determining your location on the global spheroid. These kind of timing constraints generally demand a high-tech solution. But that doesn't mean that low-tech solutions weren't equally crucial. The tie-downs that you see in the picture served two purposes: the first was to keep the vans from simply blowing away in the frequent typhoons that crossed Guam. The second was to keep the vans absolutely stationary on the surface of Guam.
The location of the photograph is at the highest point on Guam, on Halsey Drive, on Nimitz Hill, in an Admiral's backyard. By being as high as possible, a satellite's track against the horizon could be maintained for the longest possible time.
Our purpose on being on Guam (and elsewhere around the world) was twofold: to demonstrate the feasibility of satellite navigation and to participate in geodesy (to measure the shape of the earth).
At the time of the photograph above, in 1964, virtually no one in the geophysical community believed in the theory of contential drift that Alfred Wegener had proposed in the 1920's. Wegener's story is an extraordinary scientific story, one of great personal courage and determination. Wegener had based his theory of continental drift primarily on the "obvious" fit of the continents, the similarity of soil and rock types where the continents should fit together, and the similarity of species of animals (e.g., earthworms) at those points of presumed contact. However, by 1969, five years later, a complete revolution in thought had occurred. Indeed, that revolution in geophysical thought is today often compared by geophysicists to Darwin's impact on biology. And the data generated by these vans proved to be a crucial part of that revolution.
There was a great deal of excitement in all of this. First, of course, satellites were relatively new. But the second was to participate in a profound scientific revolution in human thought. Wegener died on the Greenland ice cap in 1930, long before there was any acceptance of his ideas, while attempting to measure the movement of Greenland by standard surveying techniques against the fixed star field, something we were now easily able to do in comfort in an Admiral's backyard.
However, we weren't alone in demonstrating the reality of continental drift. The other great bit of work that corroborated Wegener's ideas was the work at the Lamont-Doherty Observatory at Columbia University and their finding of a sea-floor spreading associated with an ever-widening mid-Atlantic ridge. This second bit of evidence provided the mechanism by which continents could move, evidence that Wegener never had available to him and was one of the primary reasons that his theories were so roundly condemned during his lifetime.
But the reasons we were so precisely measuring the shape of the earth weren't scientific, per se. Rather, we were doing this to obtain a very accurate map of the gravitational sphere of the earth and very accurately determine our position on it -- so as to accurately locate firing positions for nuclear submarines. If you wished to fire a submarine launched nuclear weapon from anywhere on the surface of the earth and hit a target half a world away, you must know (i) precisely where you are, and (ii) the form of the gravitational anomalies that lie in the path of the missile. The anamolies act very much like "windage." But, by knowing the three-dimensional Fourier components of the earth's gravitational spheroid, that "windage" could be accurately accounted for.
I accidentally learned the extraordinary accuracy that we were able to achieve a year later, when I was on Samoa. I cleaned the stationary attennas on the roof of our permanent building. In doing so, I had to move the entire antenna array approximately two inches. About a week later, I got a very long teletype from the Applied Physics Laboratory of Johns Hopkins University, for whom I worked, asking "What the hell happened? Did you have an earthquake?" Knowing that accuracy level was highly classified at the time, although it is fairly common knowledge now. But if there was anything truly surprising about obtaining this level of geodetic accuracy from satellites, it was the era. The United States, as a country, was only about four years into the space business in 1964. But clearly all of the theory for satellite geodesy was well deduced before the first satellites flew.
The van on the left was also filled with computers, but they were all analog. Digital computers still consumed large rooms in the early 1960s. The most elaborate of these analog computers was the Refraction Correction Unit which accounted for the dispersion and index of refraction bending of the radio signals coming from the satellites by the ionosphere (which would have otherwise given a false impression of the exact location of the satellite in three-dimensional space).
I had previously worked for RCA Service Company and NBC from 1959 to 1963 and had never heard of Hewlett-Packard during that time. Thus, when I first began work for the Applied Physics Lab/Johns Hopkins University/Physical Science Lab/New Mexico State University in 1963, the quality of the HP instruments that I now had at my disposal was a great revelation to me. The differences in the quality of the instruments that I was now using and those that I had been accustomed to was simply startling -- and that initial impression of such extraordinary quality, I have no doubt, continues to underlie much of the reason that I have been proud to have had a life-long association with Hewlett-Packard.