Satellite swarms are an emerging mission architecture which offer a flexible, robust alternative to traditional space missions. Drawing inspiration from naturally occurring swarms such as honey bees or ant colonies, satellite swarms consist of individual satellite agents working cooperatively towards a common goal. Distributed multi-agent space systems are, however, inherently problematic from the point of view of space sustainability. Given the increasingly likely prospect of operational satellite swarms, and considering that mitigating the build up of space debris is necessary to preserve our access to space and space-enabled services, the question of how to sustainably operate satellite swarms requires answering. This report presents two projects to explore how satellite swarms could be made more sustainable. In the first project we explored cooperative localisation in a satellite swarm. Using the well-studied Starlink satellite internet mega-constellation as a model swarm, we established the potential performance of cooperative localisation between 1584 Starlink satellites and 87 ground stations by calculating the Cramér-Rao Bound (CRB) at 573 simulated time steps. Our results show that the average Root Mean Square Error for localising the Starlink satellites has a constant value of approximately 10.15 m and varies between a maximum of 36.5 m and a minimum of around 2m. This result is determined primarily by the geometry of the Starlink mega-constellation and the characteristics of the inter satellite links, and gives values comparable to GNSS hardware currently on satellites. The values are also in agreement with previous research. In the second project, we introduce a satellite health indicator, a composite indicator capturing the health of a swarm satellite. We also present ongoing research modelling swarm satellites with Markov chains using CubeSat subsystems as a basis for the subsystems of swarm satellites. We also present an analysis of historical CubeSat failures using data from the CGEE CubeSat database, which shows that 18.1% of all CubeSats launched currently present a risk to space sustainability. We conclude both projects with a discussion of next steps and future research in these emerging topics.

Satellite swarms offer a high-capability mission architecture with a variety of potential applications in space exploration and discovery. Swarm-based architectures -which comprise multiple agents operating collectively as a distributed system- have been proposed for Earth observation, astronomy, planetary exploration, and heliophysics. Some of the key technology demonstration missions have already successfully flown in the past decades. The increasing interest in satellite swarms suggests that this innovative architecture will be adopted in a variety of future missions in the coming years, raising the question of how to dispose of satellite swarms at the end of their operational lifetimes. Mega-constellations or swarms comprising of numerous small satellites are difficult to track by Earth-based networks. They also increase the risk of collisions, particularly during end-of-life when these small satellites cannot be maneuvered to avoid collisions with functional satellite systems. Previously, distributed small satellite missions such as KickSat-2 and SpaceBEES 1-4 were designed to passively deorbit and burn up during atmospheric re-entry at the end of their lifetimes. However, disposing of satellite swarms outside low LEO (Low-Earth Orbit) has no trivial solution which both meets space situational awareness requirements and aligns with the philosophy of space sustainability. The distributed functionality which makes swarm missions so flexible and adaptable also means that many individual swarm agents have to be disposed of at end-of-life, rendering traditional approaches such as migration to the GEO (Geosynchronous Earth Orbit) graveyard orbit problematic. The challenges of disposing satellite swarms are as varied as the environments they could operate in - swarms used for planetary exploration will have to respect planetary protection policies while swarms engaged in Earth observation missions will have to be safely deorbited amidst an increasingly crowded LEO environment. In this paper we explore how the autonomy and distributed nature of swarms both complicates end-of-life disposal and simultaneously enables novel solutions to post-mission disposal. We then survey existing end-of-life scenarios for satellite swarms and propose a novel research approach to swarm disposal that could comply with both legal requirements and the philosophy of space sustainability.@en