Cis-lunar space-the vast region within the Moon's orbit-has become the focus of an evolving international framework whose goal it is to build on the diversity, expansion, and global nature of space activities. The United States has an enormous interest in establishing a leadership role in developing this framework. Significant research and national-security benefits are at stake. As an international leader with a growing dependence on the increasingly busy "littoral zone" of near-Earth space, the United States can help weave together the economic, social, scientific, national security, and civil aspects of space development that have evolved largely in isolation since the space age began.
The launch of the Soviet Sputnik in 1957, Apollo 11's lunar landing 40 years ago, the proliferation of satellites, the Space Shuttle program, and the International Space Station (ISS) constitute the first phase of the space age. The continued development of cis-lunar space, beyond the vibrant areas of near-Earth space, will define the next phase.