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.