The proliferation of counterspace weapons across the globe often calls into question what can be done to best protect satellites from attack. This analysis from the CSIS Aerospace Security Project addresses different methods and technologies that can be used by the United States government, and others, to deter adversaries from attack. A wide range of active and passive defenses are available to protect space systems and the ground infrastructure they depend upon from different types of threats. This report captures a range of active and passive defenses that are theoretically possible and discusses the advantages and limitations of each. A group of technical space and national security experts supported the analysis by working through several plausible scenarios that explore a range of defenses that may be needed, concepts for employing different types of defenses, and how defensive actions in space may be perceived by others. These scenarios and the findings that resulted from subsequent conversations with experts are reported in the penultimate chapter of the report. Finally, the CSIS Aerospace Security Project team offers conclusions drawn from the analysis, actionable recommendations for policymakers, and additional research topics to be explored in future work.

This overview aims to inform the public discussion of space-based weapons by examining their characteristics, potential attributes, limitations, legality, and utility. The authors do not argue for or against space weapons, nor do they estimate the potential costs and performance of specific programs, but instead sort through the realities and myths surrounding space weapons in order to ensure that debates and discussions are based on fact.

At the requests of the House Armed Services Committee and the Senate Foreign Relations Committee, OTA undertook an assessment of the opportunities and risks involved in an accelerated program of research on new ballistic missile defense technologies, including those that might lead to deployment of weapons in space. The resulting report, 'Ballistic Missile Defense Technologies', is being published concurrently with this volume. This report on 'Anti-Satellite Weapons, Countermeasures, and Arms Control' discusses additional implications of the same or similar technologies. Closely related to BMD technology, system survivability, and arms control issues are questions about the development and deployment of anti-satellite weapons. Whether or not the United States decides to deploy BMD systems in space, other military uses of space will continue to grow in importance. How can the United States respond to the potential threat to its military capabilities posed now and in the future both by Soviet military satellites and by Soviet anti-satellite weapons (ASAT)? This report examines U.S. options for countering Soviet military satellite capabilities and explores both unilateral and cooperative measures for limiting the ASAT threat. Possible unilateral steps include active and passive countermeasures as well as deterrence; possible cooperative steps include a variety of arms control agreements. The report examines the pros and cons of several illustrative "arms control regimes" for space weapons, ranging from lesser to greater limitations than now exist. It suggests that some combinations of unilateral and cooperative measures might provide more military security than either type alone. It should be recognized that the relative roles of anti-satellite weapons, countermeasures, and arms control will be strongly affected by the course followed in the development and deploymen.