Artist's impression of the Soyuz 7K-L1 en route to the Moon.
An L1 lunar complex with Proton booster top stage is being prepared in the assembly hangar
Proton booster with L1 spacecraft rollout
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 manned moon-flyby program in the Moon race. It was based on the Soyuz 7K-OK with several components stripped out to reduce the vehicle weight. The most notable modifications included the removal of the orbital module (the orbital module was replaced by a support cone and a high gain parabolic antenna) and 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. In the beginning there were serious reliability problems with both the new Proton rocket, the Proton 7K-L1, and the similar new Soyuz spacecraft. With the first four unmanned test starts (see below) being partially successful or unsuccessful, including two under 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 US Apollo 8 manned flight around the Moon, the Soviet manned moon-flyby missions lost political motivation. The first manned flight of the L1/Zond spacecraft with Alexey Leonov and Valery Bykovsky planned for the end of 1970 was cancelled.
All L1/Zond spacecraft made only unmanned automatic flights from 1967–1970, 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 the failed guidance. One direct descent re-entry was performed on a steep ballistic trajectory with 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 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 afterwards.
Two modifications of main Soyuz 7K-L1 "Zond" version were created: the powered (up to 7 tonn 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.
Despite of closest readyness for primary goal, no official open name for manned 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 manned primary goal. The intended manned use of L1/Zond spacecraft was documented in official Soviet sources at 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 sources (Big Soviet Encyclopedia's Yearbook, Kosmonavtika small encyclopedia) sporadically referred to Zond's as tests of space ships for lunar missions (omitting but meaning words manned - in difference to term space apparate used by Soviets for non-manned spacecraft).
4L -Unmanned lunar flyby -May 67 (actually launched on September 27, 1967, booster failure)
5L -Unmanned lunar flyby -Jun 67 (actually launched on November 22, 1967, booster failure)
6L -Manned lunar flyby -Jun or Jul 67
7L&8L -Manned lunar flybys -Aug 67 (7L actually launched on April 23, 1968 as Zond 1968A, booster failure; 8L actually launched on July 21, 1968, booster explosion)
9L&10L -Manned lunar flybys -Sep 67 (10L planned to launch as Zond 9, cancelled)
11L&12L -Manned lunar flybys -Oct 67
13L -Reserve spacecraft (actually launched on January 20, 1969 as Zond 1969A, booster failure;)
In July 1968 it was proposed that L1 spacecraft would be launched every month, and the first manned mission would be in December 1968 or January 1969 after 3-4 successful unmanned flights. In December 1969 dates for three manned L1 missions were set to March, May, and July 1969. Finally, in September 1969 one manned L1 mission was formally set for April 1970.