spacecraft-Doppler gravity-wave detection. II. Results

Results are presented from an experiment to detect very-low-frequency-band gravitational waves by Doppler tracking the Voyager I spacecraft at its solar oppositions in January, 1979 and March, 1980. Searches were performed for both coherent pulses and an incoherent background. No gravity-wave pulses were seen with amplitudes greater than 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ at 500-sec sample times, and no gravity-wave background was detected with an amplitude power spectral density given by ${S}_{h}={10}^{\ensuremath{-}27}{f}^{\ensuremath{-}1}$(${\mathrm{Hz}}^{\ensuremath{-}1}$), where $f$ is the Fourier frequency. The limits to sensitivity come from plasma scintillation at low Fourier frequencies and thermal system noise at high frequencies, though there appears to be tentative evidence also for a detectable level of some other low-frequency noise source, probably troposphere scintillation. Methods of getting around these limits in the future are also discussed.