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Enduring mystery of Kosmos-146

In 1967, the USSR secretly inaugurated a "stripped-down" version of the Soyuz spacecraft designated 7K-L1, and later known publicly as Zond, which was intended to fly a pair of Soviet cosmonauts around the Moon. The first test launch of the unmanned L1 test vehicle took place on March 10, 1967, however the details of this historic mission remain murky until this day. What's certain is that after four successful unmanned launches in the first half of 1967, Soviet cosmonauts were to blast off on a mission around the Moon as early as June 26, 1967! However, the flight tests did not go according to plans...

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A visualization of the 7K-L1 spacecraft during its final phase of entering orbit based on available information. The middle section of the payload fairing shown on the left could be released immediately after the separation from the third stage, while still on a ballistic trajectory, or ejected after the first firing of Block D in the initial parking orbit.

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The 7K-L1 No. 2P (Kosmos-146) mission at a glance:

Spacecraft designations 11F91, 7K-L1 No. 2P, 10L, Kosmos-146, 1967-021A, Zond
Launch vehicle 8K82K (UR-500K, Proton-K) No. N10722701 / Block D (11S824) 10L
Launch site Tyuratam, Site 81, "Left" pad
Crew Unmanned
Spacecraft mass 5,017 kilograms
Initial orbit parameters Altitude: 311.6 by 196 kilometers, inclination: 51.49 degrees
Launch date and time 1967 March 10, 14:30:32 Moscow Time
Reentry date 1967 March 11 (?)


Known unknowns of the flight program

The first flight-worthy 7K-L1 spacecraft was designated No. 2P, where "P" most likely stood for "prosteishiy" (simplified -- primarily in terms of the flight control system). (202) The vehicle was designated Number 2, because the 1P prototype was used for ground tests only.

According to the majority of reliable sources, the first two L1 launches had no ambition to fly the vehicle nowhere near the Moon or return it back to Earth, probably because many of the elements of the L1 project, such as ground control network, could not be readied in time. In his diaries as late as February 1967, Vasily Mishin, the head of TsKBEM design bureau, which built the L1 spacecraft, discusses the need to develop the long-range communications system, DRK, which would enable the flight around the Moon. In May 1967, Mishin also blamed delays in the L1 development on problems with the Argon-11 flight control computer, which indicates that this critical component was not available by the beginning of the L1 flight tests in March of 1967.

Most sources agree that the real goal of the first L1 mission was to test the performance of the Block D space tug for the first time. The flight profile apparently included at least two engine firings of Block D, enabling the spacecraft to develop the second cosmic velocity and leave the Earth's gravitational field. Based on the timing of the launch, it is also apparent that the Moon was not targeted. (50) All other details of the flight plan and final orbit parameters planned for the mission remain a mystery half a century later. It is also unknown whether the separation of the L1 spacecraft from Block D and its maneuvering was planned during this first mission.

Interestingly, in the context of the preparations for the first L1 launch, Mishin mentions the self-destruct mechanism, APO. Traditionally for the Soviet space program, the APO would be detonated if a top-secret ship was about to land outside the USSR. If Mishin's note really pertains to the first L1 vehicle, it would indicate that its descent module had a fully functional thermal protection shield designed to withstand the reentry and bring the capsule back to Earth, contradicting popular accounts of the flight program. Mishin also describes fueling of the first L1 spacecraft, which suggests that it was more than a mass dummy and it was supposed to maneuver after the separation from Block D. (774)

Final preparations push back the L1 mission

As of May 6, 1966, the first launch of the L1 spacecraft was scheduled for Oct. 20, 1966, however, as the year progressed, cumulative delays pushed the mission well into 1967.

Mishin's diaries from the period are full of notes about various issues with the L1 project, such as lack of equipment from suppliers and schedule delays with the upgrades to the ground equipment. In order to launch the L1 spacecraft, the "Left" pad at Site 81 in Tyuratam had to accommodate a much taller version of the UR-500 (Proton) rocket, which after the introduction of its two-stage version in 1965 had already become the most powerful Soviet space vehicle. This time, the UR-500 featured a streched second stage, a brand-new third stage and would be topped with the Block D upper stage, which required kerosene fuel and cryogenic liquid oxygen, unlike the three lower stages of the rocket burning hypergolic propellant. The completion of upgrades on the "Left" pad was continuously delayed from August, November and December 1966. The same work at the "Right" pad was another three months behind. Even transporting swelling numbers of workers to and from remote Site 81 in Tyuratam required Mishin's attention. (774)

On December 10, Mishin chaired a meeting of the Chief Designers Council, which reviewed preparations for a dual launch of the the Soyuz 7K-OK No. 3 and No. 4 spacecraft and the parallel work on the 7K-L1 No. 2P mission. At the time, the first L1 spacecraft was still lacking the payload fairing built at TsKBEM's Branch 3 in Kuibyshev (now Samara), as well as the 11N6110 ground diagnostics system, which was necessary for pre-launch tests. Only on December 14, Mishin got a word from Dmitry Kozlov, the head of Branch 3, that the fairing would be delivered by December 25. (774) At the time, the L1 processing schedule looked as following:

  • 1967 Jan. 1: Completion of autonomous tests of all systems for the L1 No. 2P spacecraft;
  • 1967 Jan. 20: Completion of integrated tests and the delivery of the spacecraft for fueling;
  • 1967 Jan. 25: Launch.

The first Block D for the mission was shipped to Tyuratam in the wee hours of December 14, 1966.

However before the flight-worthy L1 spacecraft could roll out to the pad, it had to be preceded by a 1M1 mockup rocket with the L1 No. 1P prototype spacecraft to do fit checks and fueling tests at the launch facility. On December 19, right after Mishin and Minister of General Machine-building, MOM, Sergei Afanasiev toured Site 81, Mishin wrote down the following timeline for the tests on the pad:

  • 1967 Jan. 8: The 1M1-L1 vehicle is ready for rollout to the launch pad;
  • 1967 Jan. 9 - 18: Testing of the flight control system (on the pad);
  • 1967 Jan. 18 - 23: Test fueling of the 1M1 mockup rocket (on the pad).

On December 20, Mishin compiled the following pre-launch processing schedule for the L1 No. 2P mission:

  • 1966 Dec. 22: Completion of all component deliveries;
  • 1966 Dec. 25: Payload fairing delivery;
  • 1966 Dec. 26: Readiness for integrated tests;
  • 1966 Dec. 27: Readiness for shake tests and polarity checks;
  • 1966 Dec. 28: Readiness for mechanical assembly of spacecraft modules;
  • 1966 Dec. 31: The completion of the spacecraft assembly;
  • 1967 Jan. 4: The completion of integrated tests;
  • 1967 Jan. 7: Final integration (of the payload section);
  • 1967 Jan. 9: Readiness for fueling;
  • 1967 Jan. 9: Readiness of the payload fairing for electric tests and test activation (postponed from Dec. 25);
  • 1967 Jan. 10: Arrival (of the spacecraft) to Processing Area No. 2 (Site 92?).

As late as December 23, 1966, Mishin pondered whether to remove the emergency escape system from unmanned L1 vehicles, probably in an effort to save time in preparation for early tests. For the same reason, he apparently looked at the possibility of skipping the installation of solar attitude control avionics, ASO, into the aggregate compartment of the L1 spacecraft. He also explored whether it would be possible to fly the L1 spacecraft without the support of a telemetry tracking ship in the Atlantic.

State Commission begins work

Sometimes in 1966, Georgy Tyulin, the veteran of the Soviet rocket industry, was appointed head of the State Commission tasked with overseeing the flight testing of the 7K-L1 system, as well as other Moon-bound spacecraft, which would be relying on the upgraded four-stage UR-500K rocket. At the time, Tyulin held the position of the First Deputy Minister of General Machine-building, MOM. The head of the OKB-52 design bureau Vladimir Chelomei, who developed Proton but lost his bid to build the circumlunar spacecraft for it to Vasily Mishin's team, did not want to play second fiddle in the commission. Instead, Chelomei delegated his deputy Yuri Trufanov, who was the leading designer of the UR-500, to sit at its meetings. Within the commission, Trufanov was appointed Deputy Technical Head. (650)


Members of the State Commission and military officers overseeing flight testing of the UR-500 (Proton) rocket in Tyuratam. Left to right: Valentin Glushko, Yuri Trufanov, Georgy Tyulin, Leonid Kaidalov, Vladimir Barmin, Ivan Pruglo, Aleksandr Konopatov, Aleksandr Kurushin, Vladimir Chelomei, Mikhail Druzhinin.

On Dec. 30, 1966, right before the New Year's Eve of 1966, Tyulin convened the State Commission to review preparations for the first L1 launch. Most of its members reported readiness to fly between 15th and 20th of January 1967, upon the completion of upgrades to the launch complex.

During the same meeting, Mikhail Ryazansky, who led the development of the flight control systems for the project, reported that an additional 100 million rubles would be required for the upgrades to the ground control network in order to communicate with L1 ships at lunar distances. Along with launch facilities, mission control was one of the issues pushing the project behind its ambitious schedule. When one month later, Nikolai Kamanin, the head of cosmonaut training, reviewed the timeline for the L1 processing, it called for the first L1 launch on Feb. 25, 1967.

On February 9, 1967, the US spy satellite Key Hole-7 (Gambit) passed over Tyuratam and snapped images of the largest Soviet rocket to date towering over the launch pad. Probably, it was the 1M1 mockup rocket with the L1 No. 1P simplified spacecraft finally delivered to the launch pad for final fit checks and fueling tests with the upgraded equipment. During tests, the mockup rocket was filled with kerosene and the alcohol-water mixture. (400)

As late as February 14, Mishin noted in his diary that flight assignment for the first two L1 vehicles was still absent. (774)

On February 16, 1967, from 15:00 to 19:30, an expanded session of the Chief Designers Council was held at the TsKBEM design bureau in Podlipki, just outside Moscow. As usual for the past year, the hectic gathering had to multi-task, first discussing the status of the Soyuz 7K-OK project, in particular the preparations for the first manned launch of Soyuz, followed by a review of the upcoming 7K-L1 missions. Despite all the pressure from the Kremlin, by that time, the launch of the first L1 spacecraft had already slipped to the end of February or beginning of March 1967.

Four days later, Kamanin got a phone call from Tyulin, who told him to plan a trip to Tyuratam on February 24 for the launch of the L1 spacecraft. However by the next day, that schedule was pushed back by three or four days, probably by last-minute technical problems. (804) In the end, top managers did not leave Moscow until March 7, 1967. The team was led personally by Vasily Mishin, Chief Designer at TsKBEM.

After its delivery to Tyuratam, the first L1 spacecraft was assembled at Site 31 on the east side of the space center and then moved to a processing building at Site 92, on the opposite end of the facility, where it was attached to the UR-500K rocket and finally rolled out to the just completed "Left" launch pad at Site 81.

On March 9, 1967, at 16:00 Moscow Time, the State Commission convened at the command post at Site 82. Just 1.5 kilometers away, the first UR-500K/L1 No. 2P vehicle was undergoing final preparations for liftoff. After reviewing the status of all systems, officials gave the green light to launch the next day. (774)

First L1 lifts off

The UR-500K (Proton) rocket carrying the 7K-L1 No. 2P spacecraft lifted off from the "Left" launch pad at Site 81 on March 10, 1967, at 14:30:33 Moscow Time. It was the fifth launch for the Proton rocket, but its first flight with the Block D fourth stage and the L1 spacecraft.

After the first three stages of the rocket accelerated its payload to a near-orbital velocity, the Block D No. 10L separated and performed a 109-second engine firing, entering an initial Earth's orbit. The third stage, lacking orbital speed, reentered the atmosphere and its remnants fell into the Pacific Ocean, east of Japan. In the meantime, a nearly 19-ton stack comprised of the L1 spacecraft and the Block D stage became the largest, heaviest Soviet spacecraft entering orbit to date.

After a period of an unpowered flight, lasting from 10 to 22 orbits, another maneuver was probably aimed to accelerate the spacecraft to a second cosmic speed of around 11 kilometers per second. According to Kamanin, the vehicle headed in the direction of the Moon. (804) However the timing of the mission did not match any convenient window for entering a trans-lunar trajectory, because the Moon was too far away from the orbital plane of the mission. (A flight to the Moon was theoretically possible but at a much greater expense of propellant and corresponding loss of payload than it would be under a favorable position of the Moon.)

According to the official history of RKK Energia, during the mission, both firings of the Block D upper stage worked as planned and all systems onboard the L1 spacecraft functioned well, with the exception of the RDM-3 radio beacon and the Thermal Control System, STR.

Due to a design error, the deactivation setup of the RDM-3 beacon was wired to a ground support network and, as a result, it could not be turned off on schedule after 40 minutes of functioning. Instead, the device kept going non-stop for 42 hours without any problems. However, the thermal control system exhibited a fall of pressure. (52)

Mysteries and confusions

Following the successful orbital insertion of the 7K-L1 No. P2 spacecraft, the Soviet press announced the mission as Kosmos-146. Two objects associated with this launch, one of which received the international designation 1967-021A, were detected by NORAD in a 190 by 310-kilometer orbit with an inclination 51.5 degrees toward the Equator. Mishin listed two similar orbital parameters in his notes for the two initial revolutions of the flight:

Orbital parameters of the 7K L1 spacecraft: (774)

Planned orbit
Orbit 1
Orbit 2
Orbital period
88.31 minutes
89.2 minutes
89.2 minutes
51.51 degrees
51.49 degrees
51.54 degrees
316 kilometers
311.6 kilometers
307.7 kilometers
189 kilometers
189 kilometers
191.5 kilometers

One can speculate that the first object was the L1/Block D stack itself, while the second could be the middle section of the payload fairing for some reason carried into orbit, instead of being ejected immediately after the separation of the third stage, which would save Block D some propellant during its first firing.

Interestingly, both initial objects in the Kosmos-146 mission disappeared on March 11, or less than 24 hours later, which could mean a reentry or a sudden maneuver to a drastically new orbit.

Around 24 hours later, another pair of objects apparently related to the same mission was detected in a slightly higher orbit with an altitude of 185 by 339 kilometers, before reentering eight or nine days later. (50)

It is well known, that the flight profile of the L1 mission, like many other spacecraft relying on Block D, called for the separation of two ullage motors from the space tug, soon after they had provided proper orientation of the stack and the beginning of the final firing of the main engine. Therefore, the two objects accompanying the Kosmos-146 mission were likely those small thruster pods ejected at the beginning of the second maneuver. What is strange is that in future L1 missions (as in most similar flights), the second firing of the Block D and the separation of the thruster pods would take place just after one revolution around the Earth, while Kosmos-146 waited for about 24 hours before the second firing. It has been long suggested that perhaps the Kosmos-146 mission simulated a potential two-launch scenario, which had been considered at the time for future manned circumlunar missions. Under such a provisional plan, the L1 spacecraft would be launched unmanned to avoid putting cosmonauts on the unproven UR-500K rocket. In case of a successful orbital insertion, the crew would follow into Earth's orbit on the 7K-OK spacecraft boosted by a more reliable Soyuz launcher. The crew would then dock with the L1 and board it for a subsequent departure toward the Moon with the help of Block D. This two-launch scenario still remained on the table at the time of the Kosmos-146 mission, before being shelved later in 1967, in favor of the one-launch flight profile.

According to Sven Grahn, a veteran space observer and a space radio expert, back on Earth, a number of radio monitors believed that they had picked short-wave signals coming from at least one object associated with Kosmos-146. Grahn explained the use of a short-wave radio (capable of sending signals globally beyond the direct line of sight of the spacecraft) by the need to keep Block D operational much longer than one orbit, which otherwise could be monitored by a tracking ship deployed in the Atlantic within a direct view of the powered portion of the flight. However, another reason could be an attempt to fly Kosmos-146 without the support of a tracking ship, exactly like Mishin had discussed in his notes at the time.

In any case, it is safe to assume that Kosmos-146 did at least begin its push away from Earth and into deep space.

In his notes, Mishin characterized the first L1 launch as "normalno" or normal, rather than success or failure, implying that the mission had gone largely OK, but could have some minor problems. In another note, he qualifies two first launches of the 7K-L1 spacecraft as successful, including the operations of Block D stages, which we now know, were not exactly flawless. (774)

For many years, it has remained unclear whether the L1 No. 2P spacecraft ended up in a highly elliptical orbit around the Earth or actually succeeded in leaving the gravitational field of our planet. A number of Soviet publications edited by Valentin Glushko in the 1980s listed Kosmos-146 among the missions reaching the second cosmic speed, though not disclosing any further details of the flight or its final orbital parameters. (2)

To add to the confusion, according to the NORAD data, not one but two objects (1967-021A and 021C) launched on March 10, appeared to be making a slight maneuver bumping their perigees from 180 to around 184 kilometers, one of which then disappeared on March 11, while another (identified as the main spacecraft) continued lingering in low orbit until March 18. The same database also shows Object 1967-021B, originating on March 12, slowly spiraling down in low Earth's orbit until March 19. Most likely, this utterly confusing picture conflates data from different objects, as it is known to be the case with a few other missions in the NORAD database.

After the end of the Cold War, newly released sources said that the second Block D maneuver aiming to accelerate Kosmos-146 to the second cosmic speed had been cut shortly before the completion of the planned 474-second burn by a command from the ground due to problems in the flight control system, which led to a deviation from the prescribed trajectory. (231) As a result, the spacecraft reentered the atmosphere and apparently burned up on March 11. (227) Why this fact was seemingly ignored by Mishin, Kamanin, Chertok and Glushko is difficult to explain. It is also unclear what happened to the descent module, which apparently had an operational reentry system. Moreover, the official history of RKK Energia claiming that the radio beacon of the spacecraft was beeping for 42 hours, also points toward a much longer mission of Kosmos-146 than its reentry on March 11.

What did they know and when did they know it?

Despite all the secrecy surrounding Kosmos-146, the US intelligence quickly sorted out some key aspects of the mission. According to a document dated March 17, 1967, (just a week after the launch) and obtained by a space historian Peter Pesavento, Kosmos-146 was immediately suspected of testing "propulsion and payload systems for manned circumlunar flight." Moreover, the document correctly deduced that a Soviet flight around the Moon had been planned during the same year.

The US intelligence had also established that the SL-9 rocket (the US name for the UR-500 Proton) which had lifted Kosmos-146, was equipped with a new upper stage for the first time, even though US experts confused the third and fourth stages. "After injection into orbit, the 3rd stage remained attached to the payload for the first 16 revolutions," the report said. A still-classified portion of the document seemingly says that US intelligence sources indicated that the second firing of what we now know was Block D had taken place during the 17th orbit of the mission. The radar then lost track of the spacecraft, suggesting that it could either have reentered the Earth's atmosphere at high speed to test the heat shield or entered a highly elliptical and even deep-space trajectory. Based on the tracking of two spherical objects estimated at three and four feet in diameter in a slightly higher orbit than that of Kosmos-146, the authors of the report favor the deep-space-trajectory hypothesis.

The US analysis also established a link between Kosmos-146 and the previous two Soyuz 7K-OK missions, at the time identified only as Kosmos-133 and Kosmos-140. However, the design of either 7K-OK or 7K-L1 spacecraft was apparently still unknown to the US intelligence at the time, because the report speculates that "the SL-9 propulsion system with an optimized third stage would be adequate to launch a modified Voskhod weighing approximately 14,000 lbs with two men aboard into a circumlunar flight."

The conclusion of the report is startling in its accuracy: "The recent acceleration in tempo of testing of systems which seem to be related to a forthcoming manned circumlunar flight suggest that the Soviets are strenuously seeking to solve remaining problems as rapidly as possible, with a view to executing this prestige-laden mission some time this year, to mark the 50th year of Communism in the USSR." (807)


Components of the RTS-9 communications system aboard the UR-500K rocket launching 7K-L1 No. 2P spacecraft:

  • Stage I: BR-9A, BR-91G-1;
  • Stage II: BR-91G-2;
  • Stage III: BR-91D;
  • 7K-L1P: BR-9L1P (two transmitters).


Ground stations supporting the 7K-L1 No. 2P mission:

  • IP-1 (Tyuratam): Stations R-11, -12, -15, -17, -18;
  • IP-2: R-21, 22;
  • IP-3: R-31-34;
  • Calculation center (VTs) Site 10: R-101, -102;
  • MIK-94: R-941;
  • IP-8: R-81-84, Railway IP -ZhIP (near Barnaul) R-61; -62;
  • NIP-3, -4, -12, Military unit, v/ch 03080.


State Commission overseeing the launch of the 7K-L1 No. 2P spacecraft as of Dec. 24, 1966 (774):

  • Georgy Tyulin (chairman)
  • Mstislav Keldysh
  • Rudenko
  • A.G. Mrykin
  • Vasily Mishin
  • Ya.I. Tregub
  • Vladimir Chelomei
  • Yuri Trufanov
  • A.G. Karas
  • Igor Yurasov
  • V.A. Kasatonov
  • Bulychev
  • Aleksandr Kurushin
  • Nikolai Kamanin
  • Ivan I. Spitsa
  • Lobov
  • Kazakov
  • G.P. Melnikov
  • N.N. Gurovsky
  • N.K. Mordasov
  • Yuri Mozhorin


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

Page editor: Alain Chabot, Last edit: March 14, 2017

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Vasily Mishin, Designer General at TsKBEM design bureau, led the flight testing of the L1 spacecraft. Credit: RKK Energia


Leading designer of the UR-500K (Proton) rocket Yuri Trufanov led its preparations for test launches with the 7K-L1 spacecraft. Credit: GKNPTs Khrunichev


Testing of the emergency escape system for the 7K-L1 spacecraft. Credit: 152


Scale model of the launch complex for the Proton rocket with the L1 spacecraft in Tyuratam. Copyright © 2002 Anatoly Zak


A four-stage Proton rocket with the Block D space tug and the 7K-L1 spacecraft shortly before liftoff.


The L1 spacecraft separates from the third stage of the UR-500K rocket during ascent to orbit. This version of the flight scenario illustrates immediate separation of the lower and middle sections of the payload fairing. Copyright © 2017 Anatoly Zak