A high performance frequency standard and distribution system for Cassini Ka-band experiment

This paper provides an overview and update of a specialized frequency reference system for the NASA Deep Space Network (DSN) to support Ka-band radio science experiments with the Cassini spacecraft, currently orbiting Saturn. Three major components, a hydrogen maser, stabilized fiber-optic distribution assembly (SFODA), and 10 Kelvin cryocooled sapphire oscillator (10K CSO) and frequency-lock-loop, are integrated to achieve the very high performance, ground based frequency reference at a remote antenna site located 16 km from the hydrogen maser. Typical measured Allan deviation is 1.6times10^-14 at 1 second and 1.7times10^-15 at 1000 seconds averaging intervals. Recently two 10K CSOs have been compared in situ while operating at the remote DSN site DSS-25. The CSO references were used operationally to downconvert the Ka band downlink received from the Cassini spacecraft in a series of occultation measurements performed over a 78 day period from March to June 2005