![]() NRL funded the development of the buffer-gas-cooled mercury ion frequency standard at Hewlett-Packard. Navy involvement has also been vital to the development of the most advanced laboratory atomic standards and the technology that will produce our next generation of high-performance atomic clocks. These three clock types-the cesium atomic beam, the rubidium gas cell, and the hydrogen maser-make up the totality of our commercially available atomic clock technology. Forty years later, this clock technology still produces the best short- to medium-term clock stability commercially available. Subsequently, with funding and technical support from NRL, the hydrogen maser clock was brought into semicommercial production. In 1960, with ONR funding, Ramsey developed the hydrogen maser. This rubidium clock technology is the workhorse of our space-based clocks today. It was tested in collaboration with NRL, using NRL’s Atomichron and a classified NRL microwave synthesizer that NBS researchers were not allowed to examine. In the late 1950s the rubidium cell clock was developed at NBS. The NRL took delivery of the first unit produced. In a remarkable effort led by Jerrold Zacharias of the Massachusetts Institute of Technology and partially funded by ONR, in 1955 the technology of the cesium atomic beam clock was transformed into a commercial product, the Atomichron, at the National Company. The result of this measurement now defines the fundamental unit of time, the second. NPL then teamed with William Markowitz of the USNO to measure the frequency of the cesium transition relative to Ephemeris Time. The National Physical Laboratory of Britain (NPL) had developed this cesium beam standard into an operable clock by 1955. ![]() (Ramsey received the Nobel Prize for this work in 1989.) This cavity design and the interrogation method developed with it have proven so essential to high-accuracy atomic clocks that they remain part of all advanced clocks today. At the heart of this device, brought into operation at the NBS in 1951, was a microwave cavity design developed in 1948 by Norman Ramsey of Harvard University, with funding from the ONR nuclear physics branch. Because its stability was no better than that of high-quality quartz oscillators, the ammonia system was quickly abandoned for the greater potential accuracy of the cesium atomic beam device. This clock was based on the measurement of a spectroscopic absorption line in ammonia. The Radio Propagation Laboratory developed the world’s first atomic clock in 1948. Radio Propagation Laboratory at the National Bureau of Standards (NBS), now the National Institute of Standards and Technology (NIST). The discussion that follows highlights those events in the history of PTTI that have had significant Navy support. Navy has maintained its leadership role in the field. Although the defense applications of PTTI now go well beyond navigation, the U.S. ![]() Naval Observatory (USNO), the Naval Research Laboratory (NRL) and, after World War II, the Office of Naval Research (ONR) were important players in the development of the technology that makes up the current state of the art in PTTI. Navy took an ever more active role in the development of emerging PTTI technologies. 1įollowing World War I and the development of the electronic oscillator and radio communications, the U.S. This device was so amazingly workable that it remained in use unchanged in its essential elements until the electronic era of the early 20th century. In the early 18th century, the Longitude Prize offered by Britain led to the development of the ship’s chronometer. Heads of several seafaring nations offered great prizes for a solution to the problem of longitude. No shipboard clocks could determine time to an accuracy sufficient for navigational purposes. Determining longitude required comparing the time at the current location with the time at a known location, say the Greenwich meridian. In the Age of Exploration, the inability to determine longitude accurately made navigation on the open seas difficult and treacherous. Naval operations and commercial shipping have been drivers for many technological developments in precision time and time interval science and technology (PTTI). ![]()
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