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L1 No. 13L launch: Beyond hope

On Jan. 20, 1969, the USSR fired an unmanned version of the L1 spacecraft intended to loop behind the Moon and return to Earth. However, as in the three previous attempts, the mission failed before reaching an initial orbit around the Earth, further emphasizing the still unreliable performance of the UR-500K launch vehicle, later known as Proton.

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Rollout of the UR-500K-7K-L1 complex to the launch pad.

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The L1 No. 13 L mission at a glance:

Spacecraft designations 7K-L1/D2 (11F91) No. 13L
Launch vehicle 8K82K UR-500K (Proton-K) Ya10723701 / Block D
Launch site Tyuratam, Site 81 "Left"
Crew Unmanned
Launch date and time 1969 Jan. 20, 07:14:36 Moscow Time
Mission results Launch failure during the operation of the second and third stages

Flight program

Vehicle 7K-L1 No. 13L (or simply 13L) was expected to follow the standard flight scenario of the L1 project with a flyby of the Moon and a return to the USSR using the so-called skip-reentry trajectory. That mission profile had already been demonstrated during the Zond-6 mission in November 1968, but, the same flight had also revealed serious technical problems at landing, therefore failing to complete the entire mission. Nor had the UR-500K rocket prove to be reliable, after failing in two attempts to reach an initial parking orbit out of eight previous launch attempts in the L1 program. More test launches with unmanned prototypes were required, if the UR-500K-7K-L1 system was ever to be certified for carrying a crew around the Moon.

Vehicle No. 13L for the latest test mission was built using the Descent Module from the L1 No. 7L spacecraft, which had never made it to orbit during another botched launch in April 1968, due to an errant activation of its escape rockets. However, the crew capsule had landed in good-enough shape to be reused for another launch attempt. (820)

The assembly of Vehicle No. 13L was near completion in August 1968, waiting for a few components, most likely those for the flight control system developed at the NII AP enterprise in Moscow. By August 15, the spacecraft was scheduled to enter integrated testing at TsKBEM's Checkout and Control Station, KIS, in Podlipki near Moscow. (774)

Final preparations

After the successful flight of NASA's Apollo-8 spacecraft in orbit around the Moon in December 1968, the political goal of the L1 project was gone. However, the already available capabilities of the L1 spacecraft could still deliver important technical benefits for the continuing, though also lagging behind the Americans, L3 lunar landing effort. At the very least, successful L1 launches could help rehabilitate the checkered performance of the UR-500K rocket, which was becoming increasingly critical for the emerging robotic lunar exploration effort. At the time, an UR-500K was already being prepared in Tyuratam for the launch of the first E8 robotic rover to the surface of the Moon.

With this backdrop, Vehicle No. 13L reached the launch pad in January 1969 to become the 10th launch campaign in the L1 program. Final preparations for the liftoff were going on just two days after the completion of the high-profile joint flight of the Soyuz-4 and Soyuz-5 spacecraft, leaving the upcoming unmanned launch without much attention from the top industry managers. As the head of cosmonaut training Nikolai Kamanin put it: the launch of Vehicle No. 13L was supervised by deputies of the deputies.

On January 20, Kamanin himself and the group of officers, as well as cosmonauts Andriyan Nikolaev and Valery Bykovsky, who supported the rehabilitation of the Soyuz-4 and -5 crews in Tyuratam, got up at 5 a.m. in the morning Moscow Time (7 a.m. local) and drove to Site 81, where Vehicle No. 13L was undergoing its final countdown for liftoff. There, they met Georgy Tyulin, who chaired the State Commission responsible for L1 flight testing, Yevgeny Shabarov, a leading test specialist from TsKBEM design bureau, and Aleksandr Kurushin, who supervised launch operations. According to Kamanin, Tyulin was confident in the success of the mission. (820)


The UR-500K/Block D rocket carrying the L1 No. 13L spacecraft lifted off from "Left" launch pad at Site 81 in Tyuratam on Jan. 20, 1969, at 07:14:36 Moscow Time.

The liftoff and ascent of the rocket as far as the eye could see looked normal and Kamanin got back into the car and drove to the command center at Site 2, where he learned that the mission had failed 501 seconds into the flight. Tyulin and Kurushin appeared at the center a few minutes later, just in time for a report from General Kutasin that the Krug radio system was picking up signals from the Descent Module of the L1 spacecraft from a region southwest of the Siberian city of Irkutsk... but on Mongolian territory.

By 08:20 Moscow Time, General Gorin delivered film with telemetry recordings from the doomed launch. The analysis of the data showed that Engine No. 4 on the second stage of the rocket had shut down 25 seconds prematurely, but that the third stage still fired and successfully separated from the second.

In his diary Kamanin claimed that the third stage had a chance to accelerate the spacecraft to the required velocity and altitude if not for the flight control system that activated the Vehicle Safety System, SBN, after it had registered an engine failure on the second stage. In turn, the SBN triggered the Emergency Escape System, SAS, prompting the separation of the Descent Module, whose landing site was then narrowed down to a point 350 kilometers from Irkutsk.

Search and rescue teams spent more than three hours to get to the spacecraft, which landed in a narrow valley surrounded by mountains up to 3,000 meters high near the border with Mongolia. (820)

However, further investigation apparently showed that the UR-500K rocket was hit with two engine failures.

First at T+313.66 seconds (or slightly more than five minutes into the flight), the 8D411K engine No. 4 (one of four engines on the second stage) shut down prematurely. That failure was attributed to an imbalance in the bearings of the turbo-pump, which caused the breakage of the turbine seal and a fire in the pump.

Still, the flight continued with three remaining engines of the second stage and the engines were cut off nominally at T+338 seconds, as the third stage took over the powered flight.

However, at T+500.03 seconds, the RD-0212 (8D48) main engine on the third stage also shut down, due to the disintegration of the fuel line leading to the pre-burner gas generator of the engine. The four-nozzle steering engine of the third stage continued firing until its nominal cutoff time at T+595 seconds, however, its thrust was far not enough to compensate for the loss of the main engine.

At T+608 seconds, the emergency escape system was activated and the Descent Module of the L1 spacecraft was separated from the rest of the stack. (231) The Descent Module then made the successful reentry into the atmosphere and safely parachuted back to Earth. (52)

The aftermath

The failure of Vehicle No. 13L delivered yet another blow to the reliability of the UR-500K rocket, which, according to Kamanin, statistically fell to 0.75. It was the 14th mission for the UR-500 rocket family since its introduction in 1965, four of which had failed. One failure was blamed on the first stage, two on the second stage and the latest accident was attributed to the third stage.

In combination with the multiple technical problems of the L1 spacecraft, the Block D space tug and their associated systems, the UR-500K-7K-L1 system was clearly too unreliable for carrying the crew. Not surprisingly, after the political rational behind the L1 project had evaporated by the success of Apollo-8, the number of opponents of the circumlunar effort inside the Soviet leadership multiplied. (820)

On Feb. 1, 1969, Kamanin quoted members of the cosmonaut group citing plans by the head of TsKBEM design bureau Vasily Mishin to kill the L1 project.

"The majority of our leaders believes it is necessary to cancel the program of the circumlunar flight aboard the L1 spacecraft," Kamanin wrote in the immediate aftermath of the Vehicle No. 13L failure. Contrary to that now overwhelming opinion, Kamanin argued that the cancellation of the L1 would throw back the Soviet lunar program by some five years. (820) Clearly in the winter of 1969, he could not yet imagine the complete failure of the USSR to put cosmonauts on the Moon.

Next chapter: Zond-7 mission

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The article by Anatoly Zak; Last update: October 24, 2020

Page editor: Alain Chabot, Last edit: January 20, 2019

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A night launch of an UR-500K rocket with a 7K-L1 spacecraft. Credit: RKK Energia


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