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Kosmos-154: Just one little mistake

In April 1967, the heat of the Moon Race turned up a notch. At a secret Soviet test site in Kazakhstan, military officers were gearing up for the second attempt to launch their largest rocket -- the UR-500K -- with a prototype of the L1 circumlunar spacecraft, while a few miles away, another team was prepping a pair of Soyuz 7K-OK spacecraft to resume Soviet manned missions after a two-year hiatus...

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A human error likely led to the premature jettisoning of thruster pods from 7K-L1 No. 3P spacecraft on April 8, 1967, stranding the vehicle in the low Earth's orbit.

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The 7K-L1 No. 3P (Kosmos-154) mission at a glance:

Spacecraft designations 11F91, 7K-L1 No. 3P, Kosmos-154, 1967-032A, B, C; Payload section: 11S824. "Zond"
Launch vehicle 8K82K (UR-500K, Proton-K) No. N10722801 / Block D No. 11L
Launch site Tyuratam, Site 81, "Left" pad
Crew Unmanned
Spacecraft mass 5,017 kilograms
Initial orbit parameters Altitude: 186 by 232 kilometers, inclination: 51.6 degrees
Launch date and time 1967 April 8, 12:00:33 Moscow Time
Reentry date 1967 April 10


Flight program for the 7K-L1 No. 3P spacecraft

Like the first mission of the 7K-L1 spacecraft in March 1967, the exact flight program and the timeline of the 7K-L1 No. 3P vehicle are still unknown. According to Boris Chertok, a key witness of the project, the second flight in the 7K-L1 project called for a flight around the Moon aimed at training mission control in navigating the spacecraft along a circumlunar trajectory. (466) Nikolai Kamanin, the head of cosmonaut training center, also made a similar claim in his diary.

However, the timing of the actual launch contradicts both of these statements. The 3P mission was scheduled to lift off well outside of a window, during which it would be practically possible to enter a trans-lunar trajectory, as shown in the analysis by Sven Grahn.

The official history of RKK Energia clearly states that the two first missions of the L1 program were limited to low Earth's orbit. The working notes of Vasily Mishin, the head of the L1 program, also hint that the two first flights were in the Earth's orbit, and, in contrast with his records regarding follow-on missions, the initial two launches are not described as planned for return back to Earth. (774)

Possibly, Chertok and Kamanin conflated the launch of Vehicle No. 3P with later missions within the L1 project.

Most sources agree that the timeline of the 3P mission was expected to repeat the first flight. Following liftoff from Site 81, the first, second and third stages of the UR-500K (Proton) rocket would accelerate the payload section 11S824, consisting of a Block D space tug and the L1 No. 3P spacecraft, to a suborbital velocity. The Block D would then conduct its first engine firing, entering an initial Earth's orbit. The second maneuver was planned for 24 hours later, either sending the spacecraft on an Earth escape trajectory or into a highly elliptical orbit.

There are no signs of preparations for the return to Earth during this mission.

Vehicle No. 3P prepares for flight

In his notes in July 1966, Vasily Mishin, indicated that the 2P and 3P spacecraft were to be ready for shipment to the launch site before the end of October 1966; however both vehicles were apparently still at their checkout and testing station in Podlipki, near Moscow, as late as December 4, 1966. But, during the same month, while the first L1 spacecraft was shipped to Tyuratam, the second vehicle (No. 3P) had entered its final testing at the assembly plant.

During preparations in Tyuratam for the first mission of the L1 program on March 9, 1967, the second vehicle was already inside the processing building at Site 31 ready for final assembly and testing. (774) Mishin's deputy Yevgeny Shabarov oversaw the work at the launch site. On the morning of April 6, Mishin and his associated flew to Tyuratam to supervise the final preparations for the mission. The State Commission met on April 7, 1967, at 16:00 Moscow Time and cleared the spacecraft for launch.

Second L1 mission lifts off

The second UR-500K (Proton) rocket carrying the 7K-L1 No. 3P spacecraft lifted off on April 8, 1967, at 12:00:33 Moscow Time (14:00 local time) from the "Left" launch pad at Site 81. Like in the previous launch, the first three stages of the Proton worked according to plan, releasing the Block-D upper stage and its payload into a suborbital trajectory. And once again, the Block D fourth stage successfully conducted its first firing, accelerating to the first cosmic velocity and entering an initial parking orbit just slightly lower than planned. (466) Mishin recorded the following orbit parameters for Vehicle 3P:

Planned orbit
Actual orbit 1
Actual orbit 2
Orbital period
89.1 minutes
88.5 minutes
189 kilometers
189.7 kilometers
188.6 kilometers
296 kilometers
232 kilometers
232.6 kilometers
Inclination toward the Equator
51.5 degrees
51.31 degrees

In the anticipation of the second maneuver on April 9, which was to be initiated by a tele-command from the NIP-16 ground station near Yevpatoria, (466) Mishin departed Tyuratam for Crimea at 16:00. However the critical firing of the main engine onboard Block D never took place, stranding the mission in its original parking orbit.

In his notes on April 9, Mishin recorded that a pair of thruster pods had been erroneously ejected from the Block D stage just 75 seconds after the completion of the first engine firing, making its second ignition impossible. (774, 231) Known as SOZ for the Russian "Ignition-providing system," the two self-contained clusters of small rocket engines were designed to keep the vehicle in the correct attitude in space and give it initial acceleration to ensure a normal flow of propellant toward the main engine in weightlessness. In a nominal flight, they were supposed to separate shortly after the main engine of the Block D had initiated its final firing of the mission.

In his diary, Kamanin blamed Mishin for not implementing a personal order from Georgy Tyulin, the head of the State Commission supervising the L1 project, to turn off the device responsible for the ejection of the SOZ thrusters after the first firing. Kamanin explained that order from Tyulin by a decision to introduce the second firing of the Block D during the latest flight. (804) That obviously can not be true, because, Block D had already fired twice during the first L1 flight.

However, Chertok does remember Tyulin calling via government line to Crimea and spilling an angry tirade at Mishin, who only mumbled in response. Chertok and Mishin could only guess that Tyulin had likely echoed a verbal assault from his own boss Dmitry Ustinov, who supervised the program for the Kremlin. (466)

According to Chertok, a human error during some upgrades in the automated control component responsible for the second firing of Block D was a culprit in the accidental release of SOZ pods. Perhaps, these upgrades themselves had been prompted by problems in the previous L1 mission.

Interestingly, in what appeared to be a to-do list dated April 9, Mishin wrote down to find out whether it would be possible to fire an engine on Block D as late as four or seven days into the flight, depending on the availability of electric power. That is close to the time period which would be required for Block D to function during a typical lunar expedition as proposed for the N1/L3 project, then still in development. (774)

The outcome

The Soviet press announced the ill-fated launch of the 7K-L1 spacecraft as Kosmos-154, obviously without much fanfare or any real details on the nature of the flight. (466) According to NORAD, the spacecraft was in a 186 by 232-kilometer orbit, with an inclination 51.6 degrees toward the Equator, where it remained for two days before reentering the Earth's atmosphere on April 10. (231)

With it, the TsKBEM design bureau exhausted its cache of simplified prototypes of 7K-L1 spacecraft. Next, Soviet engineers had to fly fully equipped L1 spacecraft, even though initially without a crew. But first, the management at the TsKBEM design bureau had to switch its full attention to the first manned launch of the 7K-OK spacecraft, which would finally resume Soviet piloted flights after a long, politically sensitive break.

On April 10, Mishin, Chertok and other officials returned to Moscow, along with the hope that all their pains and disappointments of the previous two years would soon be paid off with the headline-grabbing rendezvous mission of two Soyuz spacecraft. The team had only four days at home, marked with a celebration of the Cosmonautics Day on April 12, before heading back to Tyuratam on April 14 for the fateful launch of Soyuz-1. (466)

To be continued

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

Page editor: Alain Chabot, Last edit: April 8, 2017

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An UR-500K rocket with the 7K-L1 spacecraft on the launch pad in Tyuratam.


Block D fires its SOZ thrusters before igniting its main engine. Copyright © 2017 Anatoly Zak


The RD-58 engine propelled the Block D stage during L1 missions.


Yevgeny Shabarov, deputy to Vasily Mishin, led preparations for the launch of L1 No. 3P vehicle.