Armstrong J W
Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 238-725, 4800 Oak Grove Dr., Pasadena, CA 91109-8001 USA.
Living Rev Relativ. 2006;9(1):1. doi: 10.12942/lrr-2006-1. Epub 2006 Jan 24.
This paper discusses spacecraft Doppler tracking, the current-generation detector technology used in the low-frequency (∼millihertz) gravitational wave band. In the Doppler method the earth and a distant spacecraft act as free test masses with a ground-based precision Doppler tracking system continuously monitoring the earth-spacecraft relative dimensionless velocity 2Δ = Δ, where is the Doppler shift and is the radio link carrier frequency. A gravitational wave having strain amplitude incident on the earth-spacecraft system causes perturbations of order h in the time series of . Unlike other detectors, the ∼ 1-10 AU earth-spacecraft separation makes the detector large compared with millihertz-band gravitational wavelengths, and thus times-of-flight of signals and radio waves through the apparatus are important. A burst signal, for example, is time-resolved into a characteristic signature: three discrete events in the Doppler time series. I discuss here the principles of operation of this detector (emphasizing transfer functions of gravitational wave signals and the principal noises to the Doppler time series), some data analysis techniques, experiments to date, and illustrations of sensitivity and current detector performance. I conclude with a discussion of how gravitational wave sensitivity can be improved in the low-frequency band.
本文讨论了航天器多普勒跟踪技术，这是一种用于低频（约毫赫兹）引力波频段的当代探测器技术。在多普勒方法中，地球和一个遥远的航天器充当自由测试质量，一个基于地面的精密多普勒跟踪系统持续监测地球与航天器之间的相对无量纲速度(2\Delta v = \Delta f/f_0)，其中(\Delta f)是多普勒频移，(f_0)是无线电链路载波频率。应变幅度为(h)的引力波入射到地球 - 航天器系统上会在(\Delta v)的时间序列中引起量级为(h)的扰动。与其他探测器不同，地球与航天器约1 - 10天文单位的间距使得该探测器与毫赫兹频段的引力波波长相比很大，因此信号和无线电波在仪器中的飞行时间很重要。例如，一个突发信号在时间上被解析为一个特征信号：多普勒时间序列中的三个离散事件。我在此讨论该探测器的工作原理（重点是引力波信号和主要噪声到多普勒时间序列的传递函数）、一些数据分析技术、迄今为止的实验以及灵敏度和当前探测器性能的示例。最后，我讨论了如何在低频段提高引力波灵敏度。
