The Luna programme (from the Russian word "Luna" meaning "Moon"), occasionally called Lunik or Lunnik, was a series of robotic spacecraft missions sent to the Moon by the Soviet Union between 1959 and 1976. Fifteen were successful, each designed as either an orbiter or lander, and accomplished many firsts in space exploration. They also performed many experiments, studying the Moon's chemical composition, gravity, temperature, and radiation. Twenty-four spacecraft were formally given the Luna designation, although more were launched. Those which failed to reach orbit were not publicly acknowledged at the time and not assigned a Luna number and ones which failed in low Earth orbit were usually given Cosmos designations. The estimated cost of Luna Program was about $4.5 billion.