Autonomous Navigation for Satellite Formations
Advancing Missions Beyond Earth with Inter-satellite Radio Tracking
E. Turan (TU Delft - Space Systems Egineering)
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Abstract
Over recent years, there has been a growing interest in deep space missions involving small satellites. These missions have not only demonstrated their potential through remarkable achievements but have also spotlighted the critical role they will play in future space explorations. Simultaneously, satellite formations have gained popularity, opening up new possibilities for deep space exploration. Traditionally, these missions have relied heavily on ground-based radiometric tracking for navigation. However, ground-based operations pose several challenges, including limited tracking resources due to the increasing number of missions and high operational costs. In response to these challenges, autonomous operations, with minimal or no human intervention, emerge as a beneficial strategy, and navigation stands as a key area that could greatly benefit from autonomous operations.
In this context, various autonomous navigation strategies exist, and one of them stands out as a promising approach: Crosslink navigation, using existing systems to provide navigation solutions based on inter-satellite measurements, which primarily offers relative navigation solutions but can also facilitate absolute navigation solutions when integrated with ground-based tracking. However, absolute state knowledge, crucial for tasks such as station-keeping, often relies on ground-based commands, limiting autonomy. Alternatively, Satellite-to-Satellite Tracking (SST) data can be used for absolute state estimation, where an on-board navigation filter estimates spacecraft position and velocity, i.e. with respect to a fixed reference frame. Previous studies have shown that depending on the orbital dynamics, SST-data can provide absolute state estimation. However, this is not always straightforward, especially when inter-satellite measurements are not accurate or the observation geometry is not optimal. Since inter-satellite measurements cannot always be collected due to operational constraints, careful planning of optimal tracking windows is required. This planning can be challenging when considering possibly conflicting operational needs, such as commanding. Moreover, since radio frequency measurement techniques are used to derive navigation data, system performances must be investigated, considering varying systematic and random errors. It remained a significant challenge to determine which types of navigation data—range, range-rate, or angle—yield the most effective navigation solutions across different deep space scenarios. Since real-time navigation solutions may be needed, designing a robust on-board estimation filter can be challenging, including decisions on which parameters to be estimated or neglected.
Given these complexities, this research investigated SST-based autonomous orbit determination for satellite formations, consisting of small spacecraft, aiming to enhance current methodologies and explore new capabilities in both cislunar and deep space environments.