The flight performance of the Galileo orbiter USO

Abstract

Results are presented in this article from an analysis of radio metric data received by the DSN stations from the Galileo spacecraft using an Ultrastable Oscillator (USO) as a signal source. These results allow the health and performance of the Galileo USO to be evaluated, and are used to calibrate this Radio Science instrument and the data acquired for Radio Science experiments such as the Redshift Observation, Solar Conjunction, and Jovian occultations. Estimates for the USO-referenced, spacecraft-transmitted frequency and frequency stability were made for 82 data acquisition passes conducted between launch (Oct. 1989) and Nov. 1991. Analyses of the spacecraft-transmitted frequencies show that the USO is behaving as expected. The USO was powered off and then back on in Aug. 1991 with no adverse effect on its performance. The frequency stabilities measured by Allan deviation are consistent with expected values due to thermal wideband noise and the USO itself at the appropriate time intervals. The Galileo USO appears to be healthy and functioning normally in a reasonable manner