Spacecraft gravitational wave experiments

Doppler tracking of distant spacecraft is discussed, with emphasis on use in broadband (frequencies ~10^-4-10^-1 Hz) searches for low-frequency gravitational radiation. A short review is given of ideas about astrophysical sources, radiation times scales, and associated gravitational wave amplitudes at the Earth. The current and near-future space-based detection approaches and sensitivities are then summarized, along with a discussion of the major noise sources in space-based experiments. Finally, possible improvements in space-based detectors, including approaches that depart significantly from the current prototype systems, are briefly discussed