Because of its global range and large payload of approximately five tons, the reliable R-7 was not only effective as a strategic delivery system for nuclear warheads, but also as an excellent basis for a space vehicle. The United States' announcement in July 1955 of its plan to launch a satellite during the International Geophysical Year greatly benefited Korolev in persuading Soviet leader Nikita Khrushchev to support his plans. In a letter addressed to Khrushchev, Korolev stressed the necessity of launching a "simple satellite" in order to compete with the American space effort. Plans were approved for Earth-orbiting satellites ("Sputnik") to gain knowledge of space, and four uncrewed military reconnaissance satellites, Zenit. Further planned developments called for a crewed Earth orbit flight by 1964 and an uncrewed lunar mission at an earlier date.