Third, while space-based ASAT weapons would also generally be less costly to acquire and support than space-based ballistic missile defense systems, there does not appear to be a compelling need, on either cost or effectiveness grounds, to acquire a dedicated space-based ASAT capability—in part, because the US military already possesses or is acquiring a range of terrestrial-based weapons with significant inherent ASAT capabilities.Fourth, space-based defensive (“bodyguard”) satellites would, to a great extent, be indistinguishable from space-based ASAT weapons. Thus, such systems would likely have similar costs. In addition, their deployment would presumably have similar implications for sparking or accelerating an arms race in space. These weapons would also be incapable of protecting against some of the ASAT threats most likely to emerge in coming years. A more effective and cost-effective approach might be to rely on a range of passive countermeasures. Strengthening US space surveillance and tracking capabilities could also offer an important means of improving the security of US satellites.Fifth, although space-based weapons designed to strike terrestrial based targets, conduct ASAT attacks, or intercept enemy ASAT weapons appear to be neither necessary, nor, generally, as cost effective as terrestrial-based alternatives, in a few instances—unlike space-based ballistic missile defense systems—they appear to be relatively affordable and may even represent cost-effective options.In these cases, non-budgetary considerations, such the perceived strategic importance of the capability and the potential arms race implications of moving ahead with such a system, will have to play the dominant role in shaping programmatic and policy choices.The following discussion provides a more in-depth summary of this report’s findings concerning each of the four types of space-based weapons that the US military might consider acquiring and deploying over the next two decades.