Characteristics of the space-borne rubidium atomic clocks for the BeiDou III navigation satellite system

Abstract

<p indent=0mm>In this paper, we describe the characteristics and performance of space-borne rubidium atomic clocks for the BeiDou III navigation satellite system. The frequency stability of a rubidium atomic clock depends mainly on the signal-to-noise ratio (SNR) of the rubidium atomic transition signal, the noise of the interrogating microwave, and the physics environmental effects of the atomic system. To enhance the SNR, in the design of the physics package, we use a slotted-tube microwave cavity with a field-orientation factor higher than 0.9 and a rubidium spectral lamp with Xe as the starter gas. The light emitted from the lamp is filtered through both optical and isotope filters. We employ a low-phase-noise microwave chain, and the influence of the noise of the interrogating microwave is controlled to within 4.9<x content-type=symbol>´</x>10⁻¹³/τ^1/2. By optimizing the operating parameters, the influence of the physics environmental effects on the long-term frequency stability is reduced to a level below 3 <x content-type=symbol>´</x> 10⁻¹⁵. Two versions of the space-borne rubidium clock were produced. Version 1 has a typical performance of 1.5<x content-type=symbol>´</x>10⁻¹²/τ^1/2 for short-term stability, and 1.3<x content-type=symbol>´</x>10⁻¹⁴ and 9.4<x content-type=symbol>´</x>10⁻¹⁵ for <sc>10⁴ s</sc> and one day stabilities. For version 2, the typical frequency stabilities are 6.1 <x content-type=symbol>´</x> 10⁻¹³/τ^1/2 for short-term, 7.1 <x content-type=symbol>´</x> 10⁻¹⁵ for <sc>10⁴ s</sc> and 3.9 <x content-type=symbol>´</x> 10⁻¹⁵ for one day. Based on the current progress, we anticipate that the performance of the rubidium clocks can be further improved.