The National Aeronautics and Space Administration (NASA ) is an independent agency of the U.S. federal government responsible for the United States' civil space program, as well as research in aeronautics and space. Headquartered in Washington, D.C., NASA operates ten field centers across the US and is organized into three mission directorates: Human Spaceflight, Research and Technology, and Scien During the 1960s, NASA expanded its space science and interplanetary probe program. The Mariner program served as its flagship, launching probes to Venus, Mars, and Mercury throughout the decade. The Jet Propulsion Laboratory became the lead NASA center for robotic interplanetary exploration, facilitating significant discoveries about the inner planets. Despite these early successes, Congress became hesitant to fund further interplanetary missions, and NASA Administrator James Webb suspended all future interplanetary probes to focus the agency's resources on the Apollo program. Following the conclusion of Apollo, NASA resumed launching interplanetary probes and expanded its space science programs. The first planet targeted for intensive exploration was Venus, which shares several similarities to Earth. First visited by the American Mariner 2 spacecraft, Venus was revealed to be a hot and inhospitable planet. Follow-on missions included the Pioneer Venus project in the 1970s and Magellan, which performed extensive radar mapping of Venus's surface in the 1980s and 1990s. Later missions primarily utilized Venus flybys for gravity assists on their way to other destinations in the Solar System. Mars has long been a planet of intense fascination for NASA, being suspected of having potentially harbored life in its past. Mariner 5 was the first NASA spacecraft to fly by Mars, followed by Mariner 6 and Mariner 7. Mariner 9 was the first orbital mission to Mars. Launched in 1975, the Viking program culminated in two successful surface landings on Mars in 1976. Surface exploration w Its science programs focus on Earth observation through the Earth Observing System, heliophysics research, Solar System exploration with robotic missions such as New Horizons and the Perseverance rover, and astrophysics investigations using space-based observatories including the James Webb Space Telescope and the Hubble Space Telescope. The Launch Services Program oversees operations for uncrewed launches. The agency supports the ISS through international partnerships and highly successful commercial initiatives, such as the Commercial Crew Program and Commercial Resupply Services. Development of the Saturn V rocket was led by Wernher von Braun and his team at the Marshall Space Flight Center, deriving it from the Army Ballistic Missile Agency's original Saturn I. The Apollo spacecraft was designed and built by North American Aviation, while the Apollo Lunar Module was designed and built by Grumman. To develop the spaceflight skills and equipment required for a lunar mission, NASA initiated Project Gemini. Using a modified Air Force Titan II launch vehicle, the Gemini capsule could hold two astronauts for flights lasting over two weeks. NASA also returned to Mercury in 2004, with the MESSENGER probe demonstrating the first use of solar sailing techniques for trajectory control. NASA had been launching probes to the outer Solar System since the 1970s. Pioneer 10 became the first probe to visit the outer planets, flying by Jupiter, while Pioneer 11 provided the first close-up view of the system. Both probes eventually became the first artificial objects to leave the Solar System. The Voyager program launched in 1977, executing historic flybys of Jupiter, Saturn, Neptune, and Uranus on a trajectory extending into interstellar space. Launched primarily in the 1990s and early 2000s, the Great Observatories program comprises some of NASA's most powerful astrophysical tools. The Hubble Space Telescope was launched in 1990 via Discovery on STS-31 and proved capable of viewing galaxies 15 billion light-years away. Although a major manufacturing defect in the telescope's primary mirror threatened to cripple the mission, NASA initially compensated using computer enhancement and later flew five Space Shuttle servicing missions to install corrective optics and upgrade components. Discovery enables scientists and engineers to assemble a team to deliver a solution against a defined set of objectives and competitively bid that solution against other candidate programs. Cost caps vary but recent mission selection processes were accomplished using a $500M cost cap for NASA. The Planetary Mission Program Office is based at the NASA Marshall Space Flight Center and manages both the Discovery and New Frontiers missions. The office is part of the Science Mission Directorate. NASA Administrator Bill Nelson announced on June 2, 2021, that the DAVINCI+ and VERITAS missions were selected to launch to Venus in the late 2020s, having beat out competing proposals for missions to Jupiter's volcanic moon Io and Neptune's large moon Triton that were also selected as Discovery program finalists in early 2020. Each mission has an estimated cost of $500 million, with launches expected between 2028 and 2030. Launch contracts will be awarded later in each mission's development. ===== New Frontiers program ===== The New Frontiers program focuses on specific Solar System exploration goals identified as top priorities by the planetary science community. NASA started an annual competition in 2014 named "Cubes in Space". It is jointly organized by NASA and the global education company I Doodle Learning, with the objective of teaching school students aged 11–18 to design and build scientific experiments to be launched into space on a NASA rocket or balloon. On June 21, 2017, the world's smallest satellite, KalamSAT, was launched. === Use of the metric system === US law requires the International System of Units to be used in all US Government programs,