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arXiv 0812.2581gr-qc
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利用星载原子钟改进航天器无线电科学:应用于引力波搜索

Improved spacecraft radio science using an on-board atomic clock: application to gravitational wave searches

Massimo Tinto, George J. Dick, John D. Prestage, J. W. Armstrong

摘要:

空间用原子钟的最新进展(低质量、低功耗、频率稳定性可与地面时钟相比)可使行星际航天器无线电科学实验达到前所未有的多普勒灵敏度。增加一个机载数字接收器将允许分别测量上行链路和下行链路多普勒频率。这种单独的高质量测量允许最佳的数据组合,抑制当前主要的噪声源:来自地球大气层的相位闪烁噪声和地面天线机械振动引起的多普勒噪声。在这里,我们提供了一个一般的表达地面和机载多普勒数据的最佳组合,并计算这样的系统将有低频引力波(GW)的灵敏度。假设等离子体闪烁噪声校准与已经用多链路CASSINI无线电系统证明的校准相当,空间时钟/数字接收器仪器增强将使GW应变灵敏度为$2.0 \times 10^{-17}$,用于低频带二十倍频程($\sim0.0001-0.01$ Hz)区域内的随机极化单色GW信号。这比目前用传统的双向相干多普勒实验实现的要好一个数量级。最佳地组合同时的上行链路和下行链路观测的效用不限于GW搜索。这里讨论的多普勒跟踪技术可以以最小的增支成本进行,也可以改进未来行星际飞行任务的其他无线电科学实验(即相对论重力测试、行星和卫星重力场测量、大气和环掩星)。

英文摘要:

Recent advances in space-qualified atomic clocks (low-mass, low power-consumption, frequency stability comparable to that of ground-based clocks) can enable interplanetary spacecraft radio science experiments at unprecedented Doppler sensitivities. The addition of an on-board digital receiver would allow the up- and down-link Doppler frequencies to be measured separately. Such separate, high-quality measurements allow optimal data combinations that suppress the currently-leading noise sources: phase scintillation noise from the Earth's atmosphere and Doppler noise caused by mechanical vibrations of the ground antenna. Here we provide a general expression for the optimal combination of ground and on-board Doppler data and compute the sensitivity such a system would have to low-frequency gravitational waves (GWs). Assuming a plasma scintillation noise calibration comparable to that already demonstrated with the multi-link CASSINI radio system, the space-clock/digital-receiver instrumentation enhancements would give GW strain sensitivity of $2.0 \times 10^{-17}$ for randomly polarized, monochromatic GW signals over a two-decade ($\sim0.0001-0.01$ Hz) region of the low-frequency band. This is about an order of magnitude better than currently achieved with traditional two-way coherent Doppler experiments. The utility of optimally combining simultaneous up- and down-link observations is not limited to GW searches. The Doppler tracking technique discussed here could be performed at minimal incremental cost to also improve other radio science experiments (i.e. tests of relativistic gravity, planetary and satellite gravity field measurements, atmospheric and ring occultations) on future interplanetary missions.

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