Passive Hydrogen Maser for Space Applications

Research and development programs on the passive hydrogen maser (PHM) have been undertaken in a number of firms, government agencies, and university laboratories. In the first years of development, the PHM was cumbersome and very difficult to transport. The new generation of PHM, which is comparable in size, weight and power to the commercially available cesium standards exhibit excellent frequency stability and timekeeping ability. The frequency stability of a passive hydrogen maser is essential and exceedingly suitable as a space-based atomic clock. BENEFIT: The keys to miniaturization of the passive hydrogen maser are mainly determined by the oscillatory system. The passive hydrogen maser does not have an oscillation threshold, instead operating essentially as a very narrow microwave filter. The lack of a threshold reduces requirements on overall design, particularly regarding cavity Q, making possible a significant reduction in size, at the expense, however, of overall performance. Commercial units about half the size of an active hydrogen maser are available with fractional frequency stability of the order of a few in 10-12 at an averaging time of 1 second.