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Currently, there are roughly 35,000 monitored human-made items in orbit around our planet. Among these, only about one-third comprise active payloads: scientific and communication satellites, research initiatives, and other useful technological implementations. The remainder is classified as debris — inactive satellites, discarded rocket stages, and the remnants from numerous collisions, explosions, planned launch vehicle separations, and other “fragmentation incidents” that have transpired over humanity’s 67 years of space exploration.
The challenge of space debris is extensively documented, and it is poised to escalate in the near future as launch frequencies rise and fragmentation incidents increase correspondingly. The accumulation of debris — which encompasses an estimated 1 million items larger than 1 centimeter, in addition to the monitored objects — frequently inflicts damage on satellites, necessitates the repositioning of the International Space Station, and holds the potential to cause catastrophic collisions with increasing regularity.
To confront this challenge, in 2019, the World Economic Forum appointed a team co-led by MIT Associate Professor Danielle Wood’s Space Enabled Research Group at the MIT Media Lab to formulate a system for evaluating space mission operators based on their launch and de-orbit strategies, collision-avoidance tactics, debris generation, and data sharing, among other aspects that would facilitate enhanced coordination and upkeep of space objects. The team has devised a framework termed the Space Sustainability Rating (SSR), which was launched in 2021 as an independent nonprofit entity.
“Satellites deliver essential services that affect everyone globally by enabling us to comprehend the environment, communicate worldwide, navigate, and manage our modern infrastructure. As innovative new missions are proposed that deploy thousands of satellites, a fresh strategy is necessary to implement space traffic management. National governments and space operators must devise coordination strategies to minimize the risk of losing access to valuable satellite missions,” states Wood, who is jointly assigned to the Program in Media Arts and Sciences and the Department of Aeronautics and Astronautics (AeroAstro). “The Space Sustainability Rating contributes by assembling internationally acknowledged responsible on-orbit practices and recognizing space actors that apply them.”
France-based Eutelsat Group, a geostationary Earth orbit and low Earth orbit satellite operator, became the inaugural constellation operator with a significant deployment of satellites to receive a rating. Eutelsat submitted a mission to SSR for evaluation and was scored on a tiered rating system based on six performance modules. Eutelsat achieved a platinum rating with a score surpassing 80 percent, indicating that the mission showcased outstanding sustainability in design, operations, and disposal practices.
As of December 2024, SSR has also awarded ratings to operators such as OHB Sweden AB, Stellar, and TU Delft.
In a new open-access article published in Acta Astronautica, lead author Minoo Rathnasabapathy, Wood, and the SSR team outline the comprehensive history, motivations, and design of the Space Sustainability Rating as an incentive system that assigns a score to space operators based on their efforts to mitigate space debris and collision risks. The researchers include AeroAstro alumnus Miles Lifson SM ’20, PhD ’24; University of Texas at Austin professor and former MIT MLK Scholar Moriba Jah; and collaborators from the European Space Agency, BryceTech, and the Swiss Institute of Technology of Lausanne Space Center (eSpace).
The paper provides clarity about the inception of SSR as a cross-institutional collaboration and its evolution into a composite indicator that assesses missions across various measurable factors. The aim of SSR is to offer actionable feedback and a score that acknowledges operators’ contributions to the space sustainability cause. The paper also discusses the challenges SSR encounters in adoption and implementation, as well as its alignment with multiple international space debris mitigation directives.
SSR leverages tried and tested rating methodologies from different industries, notably Leadership in Energy and Environmental Design (LEED) in the construction and manufacturing sectors, Sustainability Assessment of Food and Agriculture systems (SAFA) in the agricultural field, and Sustainability Tracking, Assessment and Rating System (STARS) in the education sector.
“By anchoring SSR in measurable metrics and testing it across diverse mission profiles, we established a rating system that acknowledges sustainable choices and operations by satellite operators, in accordance with international guidelines and industry best practices,” remarks Rathnasabapathy.
The Space Sustainability Rating represents a non-governmental initiative to encourage space mission operators to undertake responsible measures to minimize space debris and collision risks. The paper emphasizes the roles of private sector space operators and public sector space regulators in establishing protocols to ensure that such responsible actions are carried out.
The Space Enabled Research Group continues to conduct academic research that showcases the advantages of space missions and the need for governmental oversight bodies to enforce sustainable and safe practices in space. Future efforts will highlight the necessity of a sustainability focus as practices such as satellite servicing and in-space manufacturing begin to gain prevalence.
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