The National Aeronautics and Space Administration (NASA, pronounced /ˈnæsə/) is an Executive Branch agency of the United States government, responsible for the nation's civilian space program and aeronautics and aerospace research. Since February 2006 NASA's self-described mission statement is to "pioneer the future in space exploration, scientific discovery, and aeronautics research." NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for Aeronautics (NACA). The agency became operational on October 1, 1958. NASA has led U.S. efforts for space exploration ever since, resulting in the Apollo missions to the Moon, the Skylab space station, and later the Space Shuttle. Currently NASA is supporting the International Space Station and is developing a new manned spacecraft called Orion. NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate's Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories and associated programs. NASA shares data with various national and international organizations such as from the Greenhouse Gases Observing Satellite.