|Country of origin||Soviet Union|
|Applications||Carry cosmonauts around the Moon and back to Earth|
|Derived from||Soyuz 7K-OK|
|Derivatives||Soyuz 7K-LOK|
The Soyuz 7K-L1 "Zond" spacecraft was designed to launch men from the Earth to circle the Moon without going into lunar orbit in the context of the Soviet crewed Moon-flyby program in the Moon race. It was based on the Soyuz 7K-OK. Several modifications reduced vehicle mass and increased circumlunar capability. The most notable modifications were the replacement of the orbital module with a support cone and a high-gain parabolic antenna, the removal of a reserve parachute, and the addition of the gyro platform and star navigation sensors for the far space navigation. The spacecraft was capable of carrying two cosmonauts. At the start of flight testing, there were serious reliability problems with the new Proton rocket, the 7K-L1, and the Soyuz 7K-OK that the L1 was based on.
Chief Designer Sergei Korolev had originally envisioned a crewed lunar spacecraft launched in pieces by R-7 boosters and assembled in Earth orbit. The development of Vladimir Chelomei's large UR-500 booster theoretically made it possible to do the job in a single launch. However, Chelomei also proposed his own, competing for lunar spacecraft, the LK-1, and Soviet premier Nikita Khrushchev gave his approval in August 1964. Two months later, Khrushchev was expelled from power and Chelomei lost his principal patron. At the end of the year, Korolev revived his proposal for the Soyuz spacecraft but concealed his true intentions by billing it as an Earth orbital vehicle for testing rendezvous and docking maneuvers. In October 1965, a mere three months before his death, Korolev was granted official approval for developing a crewed lunar spacecraft, which would be a modified Soyuz. This would be launched towards the Moon on a UR-500 topped with the Blok D stage under development by the OKB-1 Bureau.
Korolev originally intended to piece together the lunar Soyuz in Earth orbit because he did not believe the UR-500 was powerful enough to launch the full vehicle or that it wouldn't be safe for the crew. However, when he died in January 1966, his successor as head of OKB-1, Vasily Mishin, argued that it was definitely possible to strip down the Soyuz enough to launch it with the UR-500.
With the first four uncrewed test starts (see below) being partially successful or unsuccessful, including two under the common open name "Kosmos" as for any Soviet test spacecraft, the mission of 2–7 March 1968 and subsequent ones were the flights of the L1 spacecraft under the open designation "Zond" that were given by Soviets for test missions to far space.
After the successful United States Apollo 8 crewed flight around the Moon, the Soviet crewed Moon-flyby missions lost political motivation. The first crewed flight of the L1/Zond spacecraft with Alexei Leonov and Valery Bykovsky planned for the end of 1970 was cancelled. In addition, the Proton booster was far from being human-rated and its poor launch record made it undesirable for crewed flights.
All L1/Zond spacecraft made only uncrewed flights from 1967 to 1970, from (Zond 4 to Zond 8), and four of these five Zond flights suffered malfunctions. Test flights conducted around the Moon showed problems using their star sensors for navigation. These problems caused ballistic reentry due to failed guidance. One direct descent re-entry was performed on a steep ballistic trajectory with a deceleration of up to 20 Gs and splashed down in the Indian Ocean. Three others performed a maneuver known as "skip reentry" to shed velocity. One of those also performed an unsafe (for humans) descent of up to 20 Gs of deceleration, the other suffered main parachute failure, and only one flight - Zond 7 - would have been safe for cosmonauts.
Instrumentation flown on these missions gathered data on micrometeor flux, solar and cosmic rays, magnetic fields, radio emissions, and solar wind. Many photographs were taken and biological payloads were also flown. Zond 5 was the first spacecraft to carry a group of terrestrial creatures (tortoises being the most complex) on a circumlunar flight and return them relatively safely to Earth. Zond 5 splashed down in the Indian Ocean after descending steeply with a 20 G deceleration rate. Although unsafe for humans, these high Gs apparently didn't affect the tortoises' health, and they were reportedly able to breed afterward.
Two modifications of main Soyuz 7K-L1 "Zond" version was created: the powered (up to 7000 kg mass) Soyuz 7K-L1S "Zond-M" that were failed attempted to launch for Moon flyby on N1 rocket two times due to Soyuz 7K-LOK orbital ship-module of L3 lunar expedition complex was not ready; the Soyuz 7K-L1E "Zond-LOK" as dummy mockup of Soyuz 7K-LOK and were successfully launched on Low Earth Orbit on Proton rocket as Kosmos 382 and failed launched for Moon orbiting on third N1 rocket.
No official name for crewed Soyuz 7K-L1 "Zond" was adopted. According to Mishin's and Kamanin's memoirs, the names "Rodina" (motherland), "Ural" (Ural mountains), "Akademik Korolyov" (academician Korolyov). Also, "Zarya" (dawn) and "Znamya" (banner) were proposed for both lunar Soyuz 7K-L1 flyby and Soyuz 7K-LOK orbital ships. The information display systems (IDS) on the L1 was called "Saturn" and featured some differences from the standard 7K-OK "Sirius-7K" IDS.
Along with the remaining 7K-L1S, the Soviet Moon-flyby program was closed in 1970 without the achievement of its crewed primary goal. The intended crewed use of L1/Zond spacecraft was documented in official Soviet sources for the first time but from 1968 until 1989 this and the Moon-landing N1-L3 programs were classified and the Soviet government denied the existence of both. Near 1968 a rare open Soviet source (Big Soviet Encyclopedia's Yearbook, Kosmonavtika small encyclopedia) sporadically referred to Zonds as tests of space ships for lunar missions in contrast to the space apparate term used by the Soviets for spacecraft not capable of carrying a crew.
As of 1967, the Soyuz 7K-L1 launch schedule was:
In July 1968, it was proposed that L1 spacecraft would be launched every month, and the first crewed mission would be in December 1968 or January 1969 after 3 or 4 successful uncrewed flights. In December 1968, dates for three crewed L1 missions were set to March, May, and July 1969. Finally, in September 1969 one crewed L1 mission was formally set for April 1970.
Fifteen Soyuz 7K-L1 were built:
Main article: Moon Race § Soviet circumlunar loop flights (1967–1970)