The National Aeronautics and Space Administration is an independent agency of the U.S. federal government responsible for the United States' civil space program and for research in aeronautics and space. Headquartered in Washington, D.C., NASA operates ten field centers across the U.S. and is organized into three mission directorates: Human Spaceflight, Research and Technology, and Science. Established in 1958, NASA succeeded the National Advisory Committee for Aeronautics (NACA) to give the U.S. space program a distinct civilian orientation focused on peaceful applications. Since then, it has led most American spaceflight programs, including Project Mercury, Project Gemini, the Apollo program, Skylab, the Space Shuttle, the International Space Station (ISS) and the ongoing multi-national Artemis program.