7K-L1: Soyuz for circumlunar mission
In 1964, the USSR started a new program aimed to fly two cosmonauts around the Moon. It had a purely political goal of denying the US the most ambitious achievement in space short of the actual landing on the lunar surface. In order to meet mass restrictions for a flight toward the Moon on the UR-500 (Proton) rocket, the Soyuz had lose all its unessential systems, resulting in the 7K-L1 variant.
The unmanned version of the L1 spacecraft, officially known as Zond. Credit: RKK Energia
Key components of the 7K-L1 spacecraft and its payload section designated 11S824: 1) 7K-L1 spacecraft; 2) Block D space tug; 3) Payload fairing; 4) Launch vehicle adapter; 5) Emergency escape system; 6) The 8K82K (Proton) launch vehicle; 7) Support cone.
Known specifications of the 7K-L1 spacecraft:
The L1 was essentially a two-seat Soyuz spacecraft stripped of its habitation module to bring its mass down to as low as five tons. The spacecraft also lacked a backup parachute container, which was apparently replaced with an entrance hatch!
Because the development of the 7K-L1 variant trailed the work on the original Soyuz 7K-OK spacecraft, Korolev's engineers had a chance to integrate a number of new systems into the L1, which were not present on the Earth-orbiting Soyuz. For example, the L1 would be equipped with the first Soviet flight control computer -- Argon-11s.
The Block D (11S824) upper stage had minimal changes compared to its original design developed for the N1 rocket. A spherical oxygen tank had a cylindrical insert, which increased its volume. It also had a two-section payload fairing. (84)
The official "basic specifications" of the L1 upper composite (11S824) were approved on Dec. 31, 1965. This document listed following key development activities and upgrades within the 7K-L1 project:
The same basic specifications also planned activities on the 7K-L1 spacecraft:
At the time, the spacecraft was expected to have following specifications:
At the time, a provisional flight of the L1 spacecraft was expected to last from eight to 10 days, or up to two times longer than the maximum flight duration achieved by the USSR during the Vostok-5 mission in 1963.
For the L1 missions, the descent modules would be equipped with new, more extensive heat shield than the one developed for the Soyuz
L1 propulsion system
The L1 spacecraft would be equipped with a KTDU-53 propulsion system (also known as the S5.53 engine) developed at Isaev's design bureau.
Flight profile for the L1 project
1) Initial orbit insertion; 2) Initial parking orbit; 3) Trans-lunar insertion maneuver; 4) Trans-lunar trajectory correction; 5) Lunar flyby; 6) Second trajectory correction; 7) Third trajectory correction; 8) Separation between the descent module and the aggregate compartment; 9) Reentry and landing
During a typical L1 mission, the three-stage 8K82K rocket (a.k.a. UR-500K Proton) lifts off from Tyuratam. The payload fairing would be jettisoned with the help of small solid propellant motors during the firing of the second stage.
After the separation of the third stage, Block D (11S824) would make its first of two firings with its 11D58 engine lasting 140 seconds to enter a 205-kilometer parking orbit, with an inclination 51.5 degrees toward the Equator. (52)
After a passive flight, Block-D fires again to insert the 7K-L1 spacecraft into a trans-lunar trajectory. The 7K-L1 would then separate from Block D as it speeded toward the Moon. After the ship's actual trajectory was carefully measured against the planned parameters, the spacecraft would have an opportunity to make a correction with its own engine at a distance of around 250,000 kilometers from Earth. It would then swing behind the Moon at a minimal distance of around 2,000 kilometers conducting photography and remote-sensing experiments.
The spacecraft would head back to Earth and make another trajectory correction maneuver at a distance of around 150,000 kilometers from the home planet. The descent module with the crew would then separate and make an aerodynamic reentry into the Earth's atmosphere to land on the Soviet territory between seven or eight days after launch.
Missions of the 7K-L1 spacecraft:
Scale model of the launch complex for the Proton rocket with the L1 spacecraft in Tyuratam. Copyright © 2002 Anatoly Zak
Testing of the emergency escape system, apparently for the L1 (Zond) version of the Soyuz spacecraft. Credit: 152
A 7K-L1 spacecraft used a descent vehicle identical to the Soyuz 7K-OK spacecraft.
A 7K-L1 spacecraft, is ready for integration with its Proton launch vehicle, in preparation for the Zond-5 mission. Credit: RKK Energia
The Proton rocket with the L1 spacecraft for the circumlunar mission is poised for launch in Baikonur on Nov. 22, 1967.
The L1 spacecraft separates from the third stage of the UR-500K rocket during its ascent to orbit. This version of the flight scenario illustrates ejection of the lower and middle sections of the payload fairing immediately after the separation of the third stage. Copyright © 2017 Anatoly Zak
Block D fires its BOZ thrusters before igniting its main engine. Copyright © 2017 Anatoly Zak
Cosmonaut Aleksei Eliseev, a veteran of the Soyuz-4 and -5 mission, works inside the 7K-L1 simulator.
The Salyut-1 computer and its control panel developed specifically for the L1 project.
The RD-58 engine propelled the Block D stage during L1 missions.
L1 spacecraft during pre-launch processing.
A night launch of an UR-500K rocket with a 7K-L1 spacecraft. Credit: RKK Energia
A still from the Soviet era animation showing the trajectory of the Zond spacecraft. Click to enlarge. Credit: Roskosmos