Non-communication satellite systems include a variety of non-communication applications such as navigation services, weather monitoring, earth observation, and imaging. While it would be desirable to develop a set of spectrum efficiency metrics for non-communication satellite systems similar to what has been done for communication satellite systems, in fact, non-communication satellite systems are so unique that it is the Working Group’s current opinion that it is not practical to identify a spectrum efficiency metric that would be meaningfully extensible beyond any individual non-communication service or system. Across service types, it is not practical to identify a common spectrum efficiency metric that would apply, for example, to navigation satellites, weather monitoring satellites, earth observation satellites, and imaging satellites, because these applications are so fundamentally different. Within each non-communication service type, the service definition of each system will have great impact on the service capabilities and corresponding spectrum usage. For example, in a navigation satellite system, the spectrum usage will be driven by the location precision required, specification of the cold-start acquisition time of the receivers, and the incorporation of ancillary information such as absolute time and/or frequency references. Because of the vast range of specifications that is possible for each navigation service definition, a spectrum efficiency metric for a “generic” navigation satellite system would also not be meaningful or useful. As a specific example, the service definitions for the existing and planned navigation satellite systems (GPS, Galileo, GLONASS, and BeiDou) are so different that any metric including “total spectrum consumed” is not meaningful in a comparative sense because of the differing service capabilities. The Working Group recommends, therefore, that in the case of non-communication satellite systems, the designers and implementers of these systems should be encouraged to develop an appropriate spectrum efficiency metric for their particular system and use it as a guideline in the system design and license application processes with the objective of using spectrum efficiently. The spectrum efficiency metrics developed for each particular system can also be used to provide benchmarking against appropriate commercial standards and to allow for tracking of improvements over time. These spectrum efficiency metrics should consider including both transmitter and receiver characteristics. The Working Group is also very interested in any university research that might provide further illumination in this area.