Collision risk from performance requirements in Earth observation mission design

This paper presents a methodology to assess the collision risk of modelled Earth Observation (EO) satellites or constellations as a function of performance requirements and orbit selection. The rapid growth of the space industry over the past decade has led to an increase in the use of space data to assist with international sustainability goals, such as the use of EO to monitor indicators for the United Nations’ 17 Sustainable Development Goals (SDGs). EO committees have given recommended data parameters for various indicators including spatial resolution requirements, often requiring very high resolution data (VHR). On the contrary, the increase of satellites in space, even those whose purpose is linked to Earth-based sustainability goals, leads to higher risk of orbital satellite congestion, satellite-on-debris collision and debris generation. This presents a paradoxical situation in which the use of space data to support SDGs could become unsustainable from the perspective of operations in space. Future mission designs must consider responsible use of space whilst benefiting from its unique capabilities. The aim of the work is to provide a method of assessing and designing environmentally responsible satellite missions for Earth monitoring. Using a performance based system modelling approach, the presented method uses identified performance requirements in combination with debris flux data to concurrently estimate system mass, cross-sectional area and collision probability for a satellite or constellation at various altitudes and inclinations in LEO. This allows trends to be identified over a range of orbit regimes. Alternatively, the method can be applied to a single mission as an early design tool. Results show that for a modelled 0.5 m resolution single satellite system, collision probability peaks between 850 - 950 km, and at 80 and 120◦ inclination; this is 50 km higher than the corresponding peak in debris flux due to the consideration of the increased altitude on the system size. The emission potential for fragmentation peaks even higher around 1000 km, as the cross-sectional area and mass of the spacecraft increases with altitude and affects both the collision probability and number of fragments generated. When analysing constellations for a set coverage requirement, results show collision risk increases significantly at higher altitudes, despite requiring fewer satellites. For 2024 reference data, an increase in debris flux is seen around 550 km altitude, however the trends in collision probability relative to debris flux remain consistent. These findings show the importance of considering collision risk concurrently as part of the early design process using a method such as the one proposed in this study.