The Cassini Ka-band gravitational wave experiments

Cassini, a joint American/European interplanetary scientific mission to Saturn, will be continuously and coherently tracked for 40 days during its solar oppositions in the next three years, starting on 26 November 2001. Doppler tracking searches for gravitational waves in the millihertz frequency band will be performed by using newly implemented Ka-band (approximate to32 GHz) microwave capabilities on the ground and onboard the spacecraft, Use of the Ka-band coherent microwave link will suppress solar plasma scintillations to levels below those identified by remaining instrumental noise sources, making the Cassini Doppler tracking experiments the most sensitive searches for gravitational waves ever attempted in the millihertz frequency band. This paper provides a short review of the Doppler response to gravitational radiation, the noise sources and their transfer functions into the Doppler observable and estimates of the anticipated Cassini Doppler tracking sensitivities to gravitational radiation.