From Mercury to Pluto: A common approach to mission timekeeping

The successful launch of the New Horizons spacecraft for a rendezvous with Pluto and Charon and the continuing progress of the MESSENGER spacecraft toward Mercury now positions mankind to unlock mysteries of our solar system from Mercury to Pluto and beyond. Both missions, though very different in concept, use the same generic timekeeping system design. This paper explores how we maintain time on these spacecraft and how we establish on the ground the correlation between spacecraft time and Earth time. It further reviews the sub-millisecond correlation accuracy that has been demonstrated for the MESSENGER mission and the time accuracy we expect to achieve for that mission at Mercury and for the New Horizons mission at Pluto-Charon.