THE IN-FLIGHT FREQUENCY BEHAVIOR OF TWO ULTRA-STABLE OSCILLATORS ONBOARD THE NEW HORIZONS SPACECRAFT

摘要

The New Horizons spacecraft has been on its extensive journey to Pluto, Charon, and the Kuiper Belt since January 2006. New Horizons uses two ultra-stable quartz oscillators as onboard references for radio science and the communications transceiver. One USO is configured as primary and the other is maintained in a "warm-boot" backup mode. The implementation of the transceiver for noncoherent navigation provides the opportunity for precise determination of the intrinsic USO frequency behavior during travel through deep space. In this paper, we report on the frequency behavior observed since launch. We show the effects of general and special relativity, including the Shapiro delay, and present the differences in the spacecraft reference frequency history when observed from different frames of reference. Both USO frequency behaviors demonstrated distinct interaction with Jupiter's radiation belt during the period prior to closest approach in February 2007. The frequency drifts are -1.33 × 10~(-11)/ day and +0.98 × 10~(-11)/day, with each USO demonstrating a slight decrease in drift rate from that determined immediately after launch.