An Adaptive Method for Improving the Metrological Performance of an Onboard Time Scale Based on 87Rb and 133Cs Atomic Frequency Standards for Satellite Applications

An adaptive method is proposed for synthesizing an onboard time scale from an ensemble comprising two 87Rb and two 133Cs atomic frequency standards. The weighting coefficients are updated using diagnostic parameters, including a detector signal used as a proxy for the signal-to-noise ratio, the drift rate of the automatic frequency-control voltage, and the temperature of a critical component in each clock. Redundant pairwise phase comparisons are used to reconstruct the relative phases of the four clocks and to detect inconsistent behavior of individual standards. A two-level thermal-control architecture combining individual temperature regulation of each clock, a common heat-removal path, and precision thermostatic control of a critical internal component was developed. Laboratory tests of the precision thermostat reduced the fractional-frequency temperature coefficient from 3.28⋅10−14 to 4.9⋅10−15 K−1. The use of the developed two-level temperature stabilization system and the adaptive signal processing and synthesis system in the group frequency standard makes it possible to improve the Allan deviation by 14 % to a value of 9.011⋅10−15 at τ = 105 s. The long-term frequency stability of the onboard time scale output signal of the group frequency standard is improved by more than 15 %. Laboratory experiments demonstrated improved frequency stability, whereas simulations indicated reduced sensitivity of the ensemble to gradual degradation of an individual standard.