There is an increasing need to fly Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS) for missions related to national security, emergency management, science, and commercial applications. NASA wants to integrate UAS in the NAS, and to develop a test environment for validating concepts and technologies for UAS to safely operate in the NAS. Over 90% of future UAS flights are expected to be at low altitude, at less than 6,000 feet above ground level. Conventional air traffic management systems would be ineffective because communication and surveillance coverage are limited at these low altitudes, and communication latencies among the controller, remote pilot, and UAS vehicle will be higher than what controllers are currently used to. NASA is considering developing a low-altitude air traffic control system specifically for UAS flights, called a system for UAS Traffic Management, or UTM. Rules for structuring UTM must be developed, and fundamental requirements defined. An evaluation scheme for proposals for handling such traffic must also be developed. To address this, IAI will develop a Uninhabited Aerial System (UAS) Traffic Manager Evaluator (UTME) targeted at evaluating potential air traffic systems for handling low-altitude UAS flights. The UTME system will be built using non-proprietary hardware with non-proprietary software. It will be useful during the creation of the UTM, as alternatives can be discussed and vetted through UTME in real time. Further, UTME can be integrated with other models, through a plug-and-play interface, to provide the UTM component of an overall ATM simulation. IAI will leverage its computer science expertise in Air Traffic Management (ATM) models, its aeronautics expertise in creating appropriate trajectory generators for UAS aircraft, and its UAS expertise to develop UTME.