F.T.S. Cesium-Beam Frequency Standard

This was the first in a series of cesium pre-production frequency standards developed in the 1970s by Frequency & Time Systems Inc. (FTS), Danvers, Mass. Two cesium clocks based on this early instrument, or “brassboard,” were aboard NTS-2, the second of the Navigation Technology Satellites (NTS) launched to validate the key concepts and hardware for the Global Positioning System (GPS). Built at the Naval Research Laboratory, Washington, D.C., NTS-2 was launched in June 1977.
FTS was founded in Danvers, Mass., in 1971 and later became a subsidiary of Datum Inc. Symmetricom acquired Datum in 2002.
Martin W. Levine, “Performance of a Preproduction Model Cesium Beam Frequency Standards for Spacecraft Applications,” Proc. of the 10th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting, 1978, 169-193.
Brief description of an atomic clock
Electromagnetic waves of very specific and consistent frequencies can induce atoms to fluctuate between two energy states, and by measuring that frequency we can determine the “tick” of an atomic clock. A second in a cesium clock, for example, is defined as 9,192,631,770.0 cycles of the frequency that causes the cesium atom to jump between those states. Different atoms “tick” at different rates – strontium atoms tick about 10,000 times faster than cesium atoms – but all atoms of a given element tick at the same rate, making atomic clocks much more consistent than clocks based on macroscopic objects such as pendulums or quartz crystals.
Steven Jefferts, physicist, National Institute of Standards and Technology.
For additional background information go to:
Object Name
F.T.S. cesium-beam frequency standard
Frequency & Time Systems Inc.
Physical Description
metal (overall material)
plastic (overall material)
overall: 8 5/16 in x 10 in x 16 in; 21.11375 cm x 25.4 cm x 40.64 cm
cover: 5 1/16 in x 10 in x 16 in; 12.85875 cm x 25.4 cm x 40.64 cm
place made
United States: Massachusetts, Danvers
ID Number
catalog number
accession number
Measuring & Mapping
Time and Navigation
Science & Mathematics
Modern Physics
Science & Scientific Instruments
See more items in
Medicine and Science: Modern Physics
Time and Navigation
Time and Navigation, National Air and Space Museum
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Naval Research Laboratory
Additional Media

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