A slot architecture is developed for separating satellites in congested Sun-synchronous orbits that are a limited natural resource in low Earth orbit. A key feature of the slot architecture is a phasing rule that provides sufficient separation between slots in the vicinity of their orbital crossing points. Other features involve the discretization of orbital parameters such as semi-major axis and right ascension of the ascending node. The design parameters of the slot architecture were selected with detailed consideration of various operational aspects and orbital perturbations. A preliminary analysis indicates that slotmaintenance requirements are automatically satisfied by maneuvers that are routinely performed by current high-value Earth observation satellites to satisfy their existing mission objectives. A simulation analysis of satellites currently in Sun-synchronous orbit confirms that implementation of the proposed slot architecture would greatly reduce the frequency of close approaches between these satellites.