The purpose of this reference text is to provide information about space systems and their use for US Army and joint military operations. The intended primary users are US Army Command and General Staff College students, although military commanders, staff officers, Noncommissioned Officers, instructors, and anyone else applying space-based systems for military purposes may also find it useful. Military space operations are truly joint in their nature. There are many references to policies, programs, operations, and applications from many US Government organizations, the military services, and commercial entities. The format and contents provide a central reference regarding the environment of space, the capabilities and limitations of US satellite systems, space applications that support the military strategic, operational, and tactical levels, and space support planning considerations. In addition, the text provides a cursory background in space law, space policy, orbital mechanics, and threats to US dominance of space. The scope of this book provides a fundamental knowledge of space and space systems. The intent is for this to be a single reference source. Primary information is on space systems used by the US military. Because of the proliferation of space systems, information about other nations' systems is included on a limited basis. This reference excludes classified information to allow wider dissemination and access.