Developments Toward a Disciplined Timekeeping System for Lunar and Planetary Navigation

Abstract

The future of both lunar and planetary missions will involve the use of an increasing number of orbiters, landers and robotic rovers with ever expanding objectives over greater land area range. The coordination of these individual assets into a system capable of supporting complex exploration activities will necessarily require a local timekeeping system able to directly assist navigation, event synchronization and trunk communication back to Earth. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has derived a method for disciplining quartz Ultra-stable Oscillators (USO) to extend its superior frequency stability from 10 seconds to nearly 30 days of operating time. This is accomplished through a Kalman estimator that optimally removes the drift of the free running USO. The accuracy of the estimator is improved by periodically comparing the frequency of the USO to an atomic reference, typically located on the Earth, and transferring its accuracy to the timekeeping system via periodic uplink sessions. This is a method most frequently known as 'disciplining an oscillator'. JHU/APL will report on the accuracy of a disciplined USO that maintains better than plusmn1.5 mu seconds over 30 days and describe our roadmap toward a robust, timekeeping system capable of providing both short-term and long-term frequency stability for lunar and planetary navigation infrastructure and timekeeping.