Prioritization and Oversubscribed Scheduling for NASA’s Deep Space Network

Caroline Shouraboura, Mark D Johnston, Daniel Tran

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NASA’s Deep Space Network (DSN) is a unique facility responsible for communication and navigation support for over forty NASA and international space missions. For many years, demand on the network has been greater than its capacity, and so a collaborative negotiation process has been developed among the network’s users to resolve contention and come to agreement on the schedule. This process has become strained by increasing demand, to the point that oversubscription is routinely as high as 40% over actual capacity. As a result, DSN has started investigating the possibility of moving to some kind of prioritization scheme to allow for more automated and timely resolution of network contention. Other NASA networks have used strict static mission priorities, but if this were applied in the same way to the DSN, some missions would fall out of the schedule altogether. In this paper we report on analysis and experimentation with several approaches to DSN prioritization. Our objectives include preserving as much of each each mission’s requested contact time as possible, while allowing them to identify which of their specific scheduling requests are of greatest importance to them. We have obtained the most promising results with a variant of Squeaky Wheel Optimization combined with limiting each mission’s input based on historical negotiated reduction levels.