Development of a rubidium frequency standard for the MILSTAR satellite system

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Development of a rubidium frequency standard for the MILSTAR satellite system

McClelland, T. / Pascarn, I. / Meirs, M.

A radiation hardened Rubidium Frequency Standard (RFS) has been developed for the MILSTAR satellite system. Each satellite contains four Rb standards: 1 active, and 3 redundant units. The four RFS units must provide 3-year shelf life plus 10-year operation with a probability of success of 0.9996. This very severe reliability requirement is met by incorporating several key features in the new design. Highest component reliability is obtained by using space qualified hybrid circuitry for over 80 % of the electronics, and survivability is assured through a design which minimizes effects of radiation sensitive parameters such as offset voltages, and incorporates radiation hardened components where necessary. Lamp and resonance cell reliability are assured through quantitative analysis of Rb metal content in each cell using differential scanning calorimetry. In addition, a long term aging program has been established to measure Rb consumption rates in cells, as well as random failure rates. This program represents the first effort to determine quantitative reliability figures for Rb vacuum cells.