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A low power timing system has been developed that can achieve the following performance: Power ConsumptionFrom 5 to 41 mW Timing AccuracyWithin 5 to 70 milliseconds in 24 hours Size Less than 3 cubic Operating Temperature Range -55 to +85"C.inches

A radiation hardened Rubidium Frequency Standard (RFS) has been developed f o r t h e MILSTAR s a t e l l i t e system. Each s a t e l l i t e c o n t a i n s f o u r Rb standards: 1 a c t i v e , 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 i s met by incorporating several key features in the new design.Highest component r e l i a b i l i t y i s o b t a i n e d by using space qualified hybrid circuitry for over 80% o f the e l e c t r o n i c s , and survivability is assured through a design which minimizes e f f e c t s of radiation senqitive 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 c e l l using differential scanning calorimetry.I n addition, a long term aging program has been estab1 ished to measure Rb consumption r a t e s i n c e l l s , as well as random f a i l u r e r a t e s . T h i s program r e p r e s e n t s t h e f i r s t e f f o r t t o determine quantitative reliability figures for Rb vacuum c e l l s.

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