The Soviet crewed lunar programs were a series of programs pursued by the Soviet Union to land humans on the Moon, in competition with the United States Apollo program. The Soviet government publicly denied participating in such a competition, but secretly pursued two programs in the 1960s: crewed lunar flyby missions using Soyuz 7K-L1 (Zond) spacecraft launched with the Proton-K rocket, and a crewed lunar landing using Soyuz 7K-LOK and LK spacecraft launched with the N1 rocket. Following the dual American successes of the first crewed lunar orbit on 24–25 December 1968 (Apollo 8) and the first Moon landing on July 20, 1969 (Apollo 11), and a series of catastrophic N1 failures, both Soviet programs were eventually brought to an end. The Proton-based Zond program was canceled in 1970, and the N1-L3 program was de facto terminated in 1974 and officially canceled in 1976. Details of both Soviet programs were kept secret until 1990 when the government allowed them to be published under the policy of glasnost. Soviet cosmonauts neither orbited nor landed on the Moon.
Early concepts
As early as 1961, the Soviet leadership had made public pronouncements about landing a man on the Moon and establishing a lunar base; however, serious plans were not made until several years later. Sergei Korolev, the senior Soviet rocket engineer, was more interested in launching a heavy orbital station and in crewed flights to Mars and Venus. With this in mind, Korolev began the development of the super-heavy N-1 rocket with a 75-ton payload.
Soyuz-A-B-C and N1
In its preliminary Moon plans, Korolev's design bureau initially promoted the Soyuz A-B-C circumlunar complex (A-B-V in Russian) concept under which a two-person spacecraft would dock with other components in Earth orbit to assemble a lunar flyby excursion vehicle. The components would then be delivered by the proven middle-sized R-7 rocket. While developing the N1, since 1963, Korolev began to plan a Moon landing mission using three launches and docking. Later Korolev managed to increase the payload of the N1 to 92-93 tons (by lightening some components, adjusting the parking orbit, and increasing the number of engines in its first stage from 24 to 30), providing enough power to accomplish the mission with a single launch. There were also other improvements planned to improve the N1 for later missions, primarily by switching to liquid hydrogen in the upper stage(s).
UR-500K / LK-1 and UR-700 / LK-3 Another main space design bureau, headed by Vladimir Chelomei, proposed a competing cislunar orbiting mission using a heavy UR-500K rocket (later renamed the Proton rocket) and a two-crew LK-1 spacecraft. Later, Chelomei also proposed a Moon landing program with a super-heavy UR-700 rocket, an LK-700 lunar lander, and an LK-3 spacecraft.
R-56 The R-56 which was developed between April 1962 and June 1964 was considered for involvement with the lunar program.
Reaction to Apollo In the early stage of the Soviet and US crewed lunar programs, U.S. President John F. Kennedy proposed before the United Nations a joint Moon program, a proposal which was considered by Nikita Khrushchev. The proposal disappeared with Kennedy's assassination two months later, but nevertheless foreshadowed the Apollo-Soyuz mission, which enabled subsequently the Shuttle-Mir program and the ISS. The Soviet government issued a response to the American Apollo challenge after three years. According to the first government decree about the Soviet crewed Moon programs (Decree 655-268, ' On Work on the Exploration of the Moon and Mastery of Space '), adopted in August 1964, Chelomei was instructed to develop a Moon flyby program with a projected first flight by the end of 1966, and Korolev was instructed to develop the Moon landing program with a first flight by the end of 1967. Following the change in Soviet leadership from Khrushchev to Leonid Brezhnev in 1964, the Soviet government in September 1965 assigned the flyby program to Korolev, who redesigned the cislunar mission to use his own Soyuz 7K-L1 spacecraft and Chelomei's Proton rocket. Korolev organized full-scale development of both programs, but died after surgery in January 1966. According to a government decree of February 1967, the first crewed flyby was scheduled for mid-1967, and the first crewed landing for the end of 1968.
Moon flyby UR-500K(Proton)/L1(Zond) program
Launched by a 3-staged Proton rocket, the L1 (Zond) was a spacecraft from the Soyuz family and consisted of two or three modified modules of the main craft Soyuz 7K-OK with a total weight of 5.5 tons. The Apollo orbital spacecraft (command ship) for the lunar flyby also had two modules (command and service) but was five times heavier, carried a crew of three and entered lunar orbit, whereas the L1 (Zond) performed a flight around the Moon and came back on a return trajectory. In September 1968 Zond 5 carried the first Earth lifeforms, including two tortoises, to travel around the Moon and return safely. Planned for 8 December 1968 for priority over the US, a first crewed mission of the L1 (Zond) was canceled due to the insufficient readiness of the capsule and rocket. After Apollo 8 won the first (lunar orbit) phase of the Moon Race at the end of 1968, the Soviet leadership lost political interest in the L1 (Zond) program. A few reserve units of L1 (Zond) made unpiloted flights, but by the end of 1970, this program was canceled.
Moon landing N1/L3 program
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