Researchers at The University of Manchester have developed a new method for designing Earth-observation satellite missions. This innovative approach aims to protect the space environment while continuing to provide crucial data for global challenges such as climate change, food production, and environmental degradation.
Earth-observation satellites are vital for supporting the United Nations' 17 Sustainable Development Goals by offering data on land use, urban development, ecosystems, and disaster response. However, the rapid increase in satellite missions is making Earth's orbits more congested and hazardous, raising the risk of collisions and the generation of long-lasting space debris. Current predictions suggest the number of active satellites could grow from around 11,800 to over 100,000 by the end of the decade.
Addressing the Space Sustainability Paradox
The new model, detailed in the journal Advances in Space Research, integrates satellite mission objectives with collision risk during the initial stages of mission design. Lead author John Mackintosh states this research addresses a "space sustainability paradox":
The potential for satellites used to solve Earth's environmental and social issues to ultimately undermine the long-term sustainability of space itself.
Achieving very high-resolution satellite imagery, crucial for many applications supporting the SDGs, often requires satellites to operate at lower altitudes, which limits their field of view. Alternatively, they can operate at higher altitudes but must be larger and heavier to carry bigger optical systems. Both scenarios increase exposure to space debris and the likelihood of damaging collisions.
New Modelling Framework and Key Findings
The new framework allows satellite performance requirements and collision risk to be evaluated concurrently during mission design. It links mission requirements, such as image resolution and coverage, with estimates of satellite size, mass, the number of satellites in a constellation, and the density of debris in various regions of low Earth orbit.
Using this model, the researchers observed that collision risk is influenced significantly by satellite size, not just debris concentration. For instance, a satellite designed for 0.5-meter resolution imagery showed the highest collision probability between 850 and 950 kilometers above Earth, approximately 50 kilometers higher than the peak debris density.
The study also indicated that while higher orbits require fewer satellites for coverage, these satellites carry a greater individual collision risk due to their larger size. Conversely, lower orbits necessitate more satellites, but each can be smaller and thus less hazardous.
Future Implications
Dr. Ciara McGrath notes that this method offers a practical approach to maintaining a safe, sustainable, and usable space environment for future generations, while still providing essential data for global challenges. Professor Katharine Smith added that the method could be adapted for different Earth-observation systems and expanded to include more detailed impacts on the space environment, such as debris fragment longevity, collision probability, and the environmental effects of satellite re-entry, allowing for a comprehensive evaluation of sustainability trade-offs.