Analysis of Satellite Performance Requirements for Orbital Slot Maintenance

In the coming years the number of satellites is expected to further increase, due to reusable launch vehicles and the growing interest in space of public and private actors which are also deploying large constellations. The risk of overexploitation of the Earth's orbital environment, with the consequent increase in potential collisions, is shifting attention to the need for regulated access to space. In this context, Space Traffic Management (STM), intended as the set of means and rules to access, conduct activities in, and return from outer space safely, sustainably, and securely, becomes essential. Indeed, space has a finite capacity, despite its size, and overloading must be avoided. The problem of space environment congestion can be addressed using orbital design approaches, such as orbital slotting, aiming to minimize the risk of conjunction and the operational burden associated with planning and coordinating collision avoidance maneuvers. Indeed, the advent of large satellite constellations, especially in LEO, makes orbital slotting necessary. Orbital coordination enables the use of designed slots, optimizing orbital occupancy. Orbital slotting can involve satellites within the same orbital shell (intra-shell orbital slotting) or different orbital shells (inter-shell orbital slotting). Some techniques have been proposed in literature for both cases such as those based on 2D Lattice Flower Constellations (intra-shell slotting) and those based on frozen orbits (inter-shell slotting). However, while the intra-shell slotting usually involves satellites belonging to the same constellation, the inter-shell slotting requires coordination among satellites of different missions, making it more complex. In this regard, some concepts adopted in Air Traffic Management, such as Required Navigation Performance (RNP) can be extended to the Near-Earth orbital environment. In particular, this paper focuses on the performance requirements, mainly in terms of navigation and orbital control, which ensure that each satellite maintains its position within a defined corridor or "slot" to avoid interference with adjacent satellites. Analogous to the RNP criteria used in aircraft navigation, the concept defines a containment limit that must be met for a specified percentage of the operational period to stay within the designated slot, thus minimizing the collision risks and optimizing capacity. Any deviation beyond this tolerance could lead to potential collision risks and reduced orbital capacity. This work aims also to assess the control action needed for slotting maintenance, thus exploring the trade-off between orbital capacity and performance requirements at satellite and at STM system level.