Pioneer 10 search for gravitational waves - Limits on a possible isotropic cosmic background of radiation in the microhertz region

The nature of the response of the Doppler tracking system to a stochastic background of gravitational radiation is discussed. Using data acquired in 1981 by the Deep Space Network with the Pioneer 10 spacecraft, the authors place upper limits on the energy density of the background in three frequency bands extending from 7×10⁻⁷ to 10⁻⁴Hz, a region that has been inaccessible previously by any technique.