A Xylophone Detector in Space

We discuss spacecraft Doppler tracking for detecting gravitational waves in which Doppler data recorded on the ground are linearly combined with Doppler measurements made on board a spacecraft. By using the four-link radio system first proposed by Vessot and Levine we derive a new method for removing from the combined data the frequency fluctuations due to the Earth's troposphere, ionosphere, and mechanical vibrations of the antenna on the ground.