## 2 Literature Review  
### Space Sustainability  
In today's broader perspective, sustainability is almost always seen in terms of three dimensions: social, economic, and environmental [11]. However, in the space industry, more focus is given to the environmental aspect of space. For example, as per the UN COPOUS definition on space sustainability stated in the Introduction Section, one can interpret that the focus is placed on \"preserving outer space\". But there are other aspects that should be considered in the \"space sustainability\" definition. According to the Organization for Economic Co-operation and Development (OECD) paper on space sustainability, the concept of \"space sustainability\" encompasses a broader spectrum of considerations beyond the delineation provided by the UN COPOUS. This expanded perspective incorporates environmental, societal, occupational, and economic facets [12; 13]. Space agencies mainly focus on specific aspects of space sustainability. For instance, NASA sustainability efforts are mainly oriented towards the economic aspect [9]. ESA is focusing more on a clean space initiative that covers Eco-design, Cleansat, and active debris removal [14]. Eco-design aims to establish a shared eco-design framework for the European space sector. Cleansat concentrates on the advancement of green technologies to mitigate environmental impacts. Active debris removal targets the development of technologies necessary for managing the end-of-life of space assets [15]. For instance, in alignment with the directives outlined in their National Space Strategy, the United Kingdom (U.K.) is intensifying its initiatives in the domain of space sustainability. This commitment is exemplified by the initiation of two active debris removal phase B mission studies, a collaborative undertaking with Astroscale and ClearSpace, both of which were awarded in September 2022, amounting to a total funding of GBP 4 million. These studies are pivotal in assisting the U.K. Space Agency in determining the most viable mission concept to advance into a comprehensive design and launch phase. The culmination of these efforts is anticipated in 2026, marked by a demonstration showcasing the nation's proficiency in rendezvousing, docking with, and deorbiting two decommissioned U.K. satellites [16]. Hence, we can see private companies' and space agencies' initiatives on specific aspects of sustainability and a lack of integrated decision making considering all aspects of sustainability. In 2018, the World Economic Forum conducted a competitive solicitation for proposals and subsequently selected a consortium consisting of four entities to develop the Space Sustainability Rating [17]. This consortium is comprised of the European Space Agency, Massachusetts Institute of Technology, University of Texas at Austin, and Bryce, Space and Technology. The collaborative efforts of these organizations and the World Economic Forum were instrumental in delineating the technical and programmatic dimensions of the Space Sustainability Rating during the period spanning 2019 to 2021. The Consortium collectively contributes expertise across various domains, encompassing the modeling and assessment of the impact of space debris in Earth orbit, astrodynamics, characterization of space objects, technology policy, space economics, and an understanding of the roles played by emerging countries and private entities within the space sector [18]. The evaluation of these scores is predicated upon a comprehensive assessment of various factors. These encompass but are not limited to satellite and mission design, orbital parameters, post-mission disposal strategy, and collision avoidance strategy [19]. Furthermore, the selection and attributes of the launch provider exert influence on the overall score. Supplementary credit is accorded for the inclusion of discretionary components such as de-orbiting fixtures designed for the active removal of the object upon the fulfillment of its operational lifespan.