section_path: Human Moon landings (1969–1972)/Apollo missions
section_name: Apollo missions
paragraph_text: Apollo missions
  
  In total, twenty-four U.S. astronauts have traveled to the Moon. Three have made the trip twice, and twelve have walked on its surface. Apollo 8 was a lunar-orbit-only mission, Apollo 10 included undocking and Descent Orbit Insertion (DOI), followed by LM staging to CSM redocking, while Apollo 13, originally scheduled as a landing, ended up as a lunar fly-by, by means of free return trajectory; thus, none of these missions made landings. Apollo 7 and Apollo 9 were Earth-orbit-only missions. Apart from the inherent dangers of crewed Moon expeditions as seen with Apollo 13, one reason for their cessation according to astronaut Alan Bean is the cost it imposes in government subsidies.