Unlike the American space program, which had NASA as a single coordinating structure directed by its administrator, James Webb through most of the 1960s, the USSR's program was split between several competing design groups. Despite the remarkable successes of the Sputniks between 1957 and 1961 and Vostoks between 1961 and 1964, after 1958 Korolev's OKB-1 design bureau faced increasing competition from his rival chief designers, Mikhail Yangel, Valentin Glushko, and Vladimir Chelomei. Korolev planned to move forward with the Soyuz craft and N-1 heavy booster that would be the basis of a permanent crewed space station and crewed exploration of the Moon. However, Dmitry Ustinov directed him to focus on near-Earth missions using the very reliable Voskhod spacecraft, a modified Vostok, as well as on interplanetary uncrewed missions to nearby planets Venus and Mars.