NASA is undertaking a trio of closely-related programs to continue human space exploration beyond low-Earth orbit: the SLS vehicle; the Orion capsule, which will launch atop the SLS and carry astronauts; and the supporting ground systems. As a whole, the efforts represent NASA's largest exploration investment over the next decade, potentially as much as $22 billion, to demonstrate initial capabilities. Beyond 2021, NASA plans to incrementally develop progressively more-capable SLS launch vehicles complemented by Orion capsules and ground systems. This book examines the scope of NASA's preliminary cost estimates for the three programs. It examines the SLS program's progress toward and risks for its first test flight in 2017; and the extent to which the SLS program has plans in place to achieve its long-term goals and promote affordability.