The rapid growth in satellite deployments, particularly with the emergence of large constellations, has amplified concerns over the sustainability of the orbital environment. Space mission operators can utilize different mechanisms during the design and operation of their missions to adhere to space sustainability best practices. This paper presents the Space Sustainability Rating (SSR), a novel initiative developed to incentivize satellite operators to adopt sustainable practices throughout mission lifecycles, and provides an overview of its history, design, and implementation. The SSR is a composite indicator that evaluates missions across multiple dimensions, including debris mitigation, collision avoidance, and data-sharing practices, providing operators with actionable feedback and recognition for their contributions to space sustainability. Drawing on methodologies from successful sustainability rating systems in other industries, such as LEED, the SSR combines simulations, questionnaires, and evidence verification to assess compliance with best sustainable practices. The rating framework is structured into six main modules, complemented by an overarching verification module, and is applicable across all mission phases. This paper discusses the challenges addressed by the SSR, its alignment with international debris mitigation guidelines, and its role in fostering voluntary sustainable behavior among space operators.