The past, present, and future of atomic time and frequency

Article Abstract:

Magnetic resonance experiments with molecular beams first measured the interactions of nuclear magnetic moments with external magnetic fields in 1938. The possibility of atomic clocks was first envisioned in 1939. The separated oscillatory field method, invented in 1949, provided narrower resonances, eliminated first order Doppler shifts and was usable at higher frequencies. Initial work on a separated oscillatory field atomic cesium clock was begun in 1952, the first atomic beam apparatus used as a frequency standard was built in 1955. Several other atomic and molecular clocks were developed, along with microwave absorption devices that use molecular resonances. Kleppner and Ramsey invented the atomic hydrogen maser, Townes and Schawlow discovered the possibility of applying maser principles to infrared and light frequencies. The first successful laser was made by Maiman.

Standard, Standardization, Time measurement, History, Lasers, Technical, Laser, Frequency

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Fixed satellite service frequency allocations and orbit assignment procedures for commercial satellite systems

Article Abstract:

The International Telecommunication Union, a United Nations agency, allots radio spectrum for radio services, sets procedures to coordinate use of frequency assignments, and registers radio frequency assignments to avoid harmful interference between radio stations belonging to different countries. The ITU WARC on Space Radio Services (ORB-88) improves the regulatory procedures and sets up an allotment plan for frequency bands used by commercial satellite operations. ORB-88 will impact the US's ability to satisfy US domestic satellite requirements, but the impact will be minimal in the short-term. The development of some multiple frequency band, multiple service satellites may be constrained by the international regulatory burden that must be assumed when implementing several frequency bands and radio services on the same spacecraft.

Satellite communications, Space Craft, Radio Frequency, International Organizations, technical, Radio Frequency Interference

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