Belka and Strelka

No. 6

Vostok-1K No. 6


Vostok-3A No.1


Vostok-3A No. 2


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Vostok prototype lost on reentry

On December 1, 1960, the USSR launched the fourth prototype of the piloteless Vostok spacecraft to prepare the pioneering mission of a human in space. The day-long orbital flight went flawlessly until the time came to return its ball-shaped pilot capsule with two dogs onboard back to Earth.

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Vostok-1 (1K No. 5) mission at a glance:

Spacecraft designation Third Korabl-Sputnik, Vostok-1 (No. 3), 1K No. 5
Launch vehicle 8K72 L1-13 (Vostok)
Spacecraft mass 4,563 kilograms
Launch Site Tyuratam, Site 1
Launch date and time 1960 Dec. 1, 10:30:04.3 Moscow Decree Time
Orbital altitude 187.3 x 265 kilometers
Orbital inclination 64.97 degrees
Orbital period 88.47 minutes
Flight duration 1 day
Landing 1960 December 2 (Descent Module lost)
Crew No


Mission history

The successful return of the dogs Belka and Strelka from orbit demonstrated the safe performance of the Vostok spacecraft in all stages of the flight from launch to landing. In the next step, the engineers at Sergei Korolev's OKB-1 design bureau needed to prove that their triumphant feat in August 1960 was not just a lucky strike. Otherwise, they were getting increasingly confident to predict the first human mission aboard Vostok before the end of 1960.

On September 1, 1960, Dmitry Ustinov, who supervised the Soviet rocket industry, and three other top defense officials sent a note informing the Central Committee of the Communist Party on the planned rocket and space developments for the rest of the year. The document promised to complete the assembly of two fresh Vostok vehicles during the same month and perform their launches in October or November. Moreover, the two remaining vehicles being build within the piloted Vostok program would be launched by the end of 1960, the note said. According to the document, these launches would clear the way to the testing of the Vostok-2 military photo- and radio-reconnaissance satellite in the first quarter of 1961.

Just 10 days later, Ustinov wrote to the Central Committee that the recent success with the launches of the Vostok-1 series gave new reasoning for the timing of the first human flight into space. The note signed (and probably drafted) by Korolev said that "the (latest) work on the planned technical solutions opens the possibility for completing the development of the Vostok-3A spacecraft and resolving the issues of human space flight aboard this vehicle in 1960."

The document reiterated the plans to launch either one or two Vostok-1 prototypes, apparently depending on the performance of the first of those two missions. A pair of Vostok-3A spacecraft, fully configured for piloted missions, but without the cosmonaut onboard, would be performed during the November-December period, followed by the first launch of a human aboard the Vostok-3A variant in December 1960, the note proposed. To free the resources of the industry for this super-ambitious schedule, the document proposed to postpone the development and launches of Elektron scientific satellites, E-7 lunar orbiters, Vostok-2 reconnaissance satellites and E-6 lunar landers. The document was still committing the industry to meeting the launch window to Venus in January 1961.

On September 14, Ivan Serbin, who oversaw the defense industry at the Central Committee, endorsed the plan with the exception of the delay of the Vostok-2 project. In turn, on October 11, 1960, the Central Committee approved the schedule and declared the launch of Vostok-3A with a pilot onboard to be of a special importance. (509) Apparently, the news about the development of the Mercury project in the United States aiming to put a man in space played a role in accelerating the Soviet schedule.

Despite its top priority, the fourth Vostok-1 spacecraft reached the launch pad behind schedule, first of all due to the hectic campaign to send the first pair of robotic probes to Mars in October 1960. Before the end of the same month, the Nedelin disaster delivered another blow to the morale of the personnel at the Tyuratam launch site. (466) The 1K No. 5 spacecraft arrived at Tyuratam for pre-launch processing on November 5, followed by the 8K72 No L1-13 rocket on November 9, 1960.

Flight program for the fourth Vostok mission

Ejection seat

Although pilots were expected to land inside their capsule during Vostok follow-on missions, the ship's bulky ejection seat would still be needed for emergency escape during the launch.

During much of 1960, one of the biggest challenges facing the developers of the Vostok spacecraft was its emergency ejection system allowing cosmonaut to bail out from the failing rocket all the way up to the end of the operation of the first stage. In 1959, the Flight Research Institute, LII, designed a special thermal cacoon and a stablization system to protect the pilot during descent from stratospheric altitudes starting between 60 and 125 kilometers (463), however the concept had never been proven. (52)

By the end of August 1960, Department 9 at OKB-1 proposed Korolev, among other things, to drastically simplify the design of the escape system by limiting the operational altitude of the ejection seat to just four (52) or five kilometers (463). As a result, the pilot could bail out in the open ejection seat protected only by a pressure safety suit. In case of a fatal problem at a higher altitude, the flight control system would have to shut down the rocket's engines, jettison the payload fairing and cut the harness attaching the Descent Module to the Instrument Module. The capsule could then "naturally" separate from the failing vehicle and land according to a nominal flight profile.

Korolev signed off on that risky scheme but asked to provide a backup for the Vostok's braking engine – another potential Achilles' heel in the mission return scenario. Fitting another propulsion system into the Vostok that late in the project was clearly out of the question, but a ballistic specialist named Zubko completed a study of an alternative return method without any hardware changes. (463) If the spacecraft could be put into orbit low enough relative to the upper atmosphere, it would decay naturally as a result of friction with the rarified air. (52) Experts plotted an elliptical orbit whose perigee (lowest point) would cause the vehicle to reenter after 10 days or less, for which Vostok could provide adequate life support to its passenger.

The plans for the new flight trajectory were ready ahead of the fourth mission of the Vostok prototype in the Fall of 1960. At the time, Korolev actively "positioned" the development of the piloted Vostok-3A variant as the ultimate military reconnaissance vehicle capable of delivering superior data, compared with robotic versions of the Vostok spacecraft and with the known American military satellites, such as Samos. The Chief Designer drove that point home (or rather to the Central Committee) on November 16 in a secret letter, as usually signed by Ustinov and other Korolev's superiors. The document said that the upcoming launch of the Vostok-1 prototype would test key parameters of the follow-on Vostok-3A variant, first of all its capability to function in an elliptical orbit with a perigee (lowest point) of around 180 kilometers. Korolev also promised to test solar orientation of the spacecraft allowing a controlled braking maneuver and deorbiting of the capsule with commands from the ground, followed with a ballistic descent and landing at the projected landing site. (A switch to solar orientation as the primary method of attitude control was made in the wake of failures of the original infra-red system in previous flights.)

The nominal mission of the latest Vostok prototype was expected to last one day, but in case of a failure to reenter, the spacecraft would self-destruct after 60 hours in orbit, the document said. The November 16 letter detailing the flight plan was supplemented with the draft of a public statement to be approved by the Central Committee and to be released after a successful launch. All these documents were approved by the Kremlin on November 24.

For the fourth Vostok launch, a pair of four-year old, light-colored female dogs named Mushka (little fly) and Pchelka (little bee) were placed into the ejectable GKZh container inside the Descent Module. (52) As before, a pair of Seliger TV cameras was installed to image a profile of one dog and the front of another. Key physiological parameters of the dogs were measured with a set of sensors, capable of transmitting their data to ground stations during multiple passes of the spacecraft over the Soviet territory.

As usual, the group of live creatures aboard the Descent Module was complemented with guinea pigs, mice and flies, as well as various biological specimens such as plant seeds, bacteria, viruses and even rabbit's bone marrow. The Bios experiment aboard the spacecraft was designed to attempt the first insemination in space by using fish eggs and sperm mixing during the flight inside an automated chamber.

Fourth Vostok enters orbit

The fourth Vostok spacecraft lifted of from Tyuratam on December 1, 1960, at 10:30 Moscow Time, and reached a nominal orbit less than nine minutes later. As originally planned, the 187 by 265-kilometer orbit was calculated to be low enough to ensure the possibility for a natural reentry of the spacecraft within 10 days. (According to another source, the spacecraft entered a 180 by 249-kilometer orbit with an orbital period of 88.47 minutes). (84) In any case, the fact of the lower orbit than the one used in the previous launches, and the resulting shorter orbital period did not go unnoticed in the West, even though its purpose was not explained publicly at the time. (50)

The official Soviet press announced the mission as the Tretiy Korabl- Sputnik or Third Spacecraft-Satellite. (2) It was sometimes referred to as Sputnik-6 in the West, based on the number of known Soviet space launches at the time. The Soviet Pravda daily also quoted the Reuters news agency in London as saying that its radio stations had received signals from the sputnik.

Behind the scene, ground controllers reported smooth operations of all systems aboard the spacecraft. (466) A total of 12 communications sessions had been conducted between the Vostok and the Soviet ground stations during a day-long flight. (781)

Fatal landing

On December 2, 1960, as the Vostok-1K No. 5 was making its 17th revolution around the Earth and starting its second day in space, ground controllers issued commands for the return to Earth during the 18th orbit of the mission. At the time of the braking maneuver, the Signal-Yupiter ground station in Tyuratam, capable of receiving telemetry from the onboard Signal transmitters at distances exceeding 10,000 kilometers (463), was able to downlink information from the spacecraft. Telemetry officers Starlychanov and Shlyapnikov immediately deciphered the fresh data, revealing that despite the activation of the braking engine, the subsequent separation of the Descent Module and the Instrument Module had not taken place. Next, ground controllers registered the activation of the APO self-destruct mechanism, followed by the abrupt disappearance of radio signals from the spacecraft. Given the gravity of the situation, Vladimir Poroshkov, the commanding officer at the Signal-Yupiter facility, asked his telemetry experts to re-check their interpretation of the data. They expressed their absolute confidence in what they were seeing. Poroshkov then rushed to the ZAS telegraph station located at the SEV building located almost a kilometer away. In his presence, the telegram with the devastating news was sent to the NII-4 institute in Bolshevo, the nerve center of the mission.

Poroshkov had barely returned to his post, when a call from the telegraph station relayed a demand from NII-4 to re-confirm his report. To Poroshkov such a request meant that either his data did not match that received by other ground stations or his facility was the only one which was able to receive the (post-braking maneuver) signals. The only other explanation for the doubts in his data that Poroshkov could come with was that officials at NII-4 were looking for an excuse to drag their feet with delivering terrible news about the mission up the chain of command. Poroshkov once again asked his onboard telemetry specialists to re-check all the data, which they begrudgingly did despite being confident it would not change the result. Poroshkov himself pored over the graphs and came to the same conclusion. Yet, he then got a call from the command post at the IP-1 ground station in Tyuratam informing him that Kama antennas at IP-1 and IP-1B sites (in Tyuratam) were still receiving signals from the spacecraft! Poroshkov responded that it was impossible since the spacecraft had self-destructed, but the caller on the other end of the line insisted that Kamas had "seen" the vehicle. Poroshkov's team then requested the exact azimuth for the signal direction and after some pause, the caller apologetically admitted that the two Kama stations (at IP-1 and IP-1B sites separated by 23 kilometers) were simply bouncing request and respond signals from each other! This news was met with great laughter at the Yupiter-Signal station, but others involved in the mission were not laughing. (537)

The subsequent analysis apparently revealed that due to a problem with the flight control system, the attitude control thrusters failed to place the vehicle in the correct orientation against the direction of the flight for a braking maneuver. As a result, the TDU braking engine failed to deliver enough push for the planned reentry, leaving the spacecraft on a shallow descent trajectory with an unpredictable landing point.

According to one source, the spacecraft made an additional half orbit around the Earth before reentering beyond the range of Soviet tracking assets. (649) According to Korolev's summary of Vostok missions presented to the State Commission on March 29, 1961, the spacecraft made 1.5 orbit after its braking maneuver. (781) The same report also claimed that the separation between Descent and Instrument Modules had gone as planned and there was one more communications session with the Instrument Module before it finally plunged into the atmosphere. (84) (One might wonder whether that interpretation of events was a result of the confusion with the antenna guidance in Tyuratam).

Korolev's deputy Boris Chertok, responsible for flight control systems, remembered one of the ballistic experts named Svyatoslav Lavrov quickly plotting a graph showing the descent trajectory terminating in Eastern China, though Chertok did not clarify whether it would happen during the planned landing orbit or after an extra loop around the planet. According to Chertok, the situation prompted a frantic discussion among flight managers gathered at Site 2 in Tyuratam on the further course of actions. In his memoirs, Chertok remembered expressing confidence that the spacecraft would self-destruct leaving only small debris to reach the ground. Indeed, the word soon came from a ground station in Ussuriisk in the Soviet Far East that radio-transmission from the spacecraft ceased suddenly before it could reach the atmosphere. (466)

To prevent the landing of top-secret capsules beyond the Soviet territory, all unpiloted Vostoks were equipped with the self-destruct mechanism, APO, whose timer was activated simultaneously with the firing of the braking engine.

During the flight of Vostok 1K No. 5, the APO was automatically triggered after the flight control system missed the required time marker for the atmospheric entry measured by a g-force sensor. (231) Though unplanned, the APO system test proved its deadly efficiency for future operations aboard Soviet reconnaissance satellites, which closely resembled the piloted Vostok spacecraft. Obviously, such a "successful" validation cost two dogs their lives.

On December 2, the official Soviet press published an update on the mission, saying that by 12:00 Moscow Time, the spacecraft continued its orbital flight, but all planned tests had been completed. The release also said that TV equipment aboard the spacecraft had provided ground control with observations of the animals who were in good shape. The statement concluded that "upon the reception of the necessary data, a command was issued for the descent of the spacecraft-satellite back to Earth. Due to a descent along a non-nominal trajectory, the spacecraft-satellite ceased to exist during the entry into the Earth's atmosphere."


Page author: Anatoly Zak; Last update: March 25, 2021

Page editor: Alain Chabot; Last edit: December 1, 2020

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insider content



1K spacecraft under assembly in Tyuratam.


The Seliger TV camera similar to the one which was likely installed on early Vostok spacecraft.



TV images of dogs captured during training a few months before the launch of the third Vostok-1K spacecraft. Credit: Roskosmos



Publicly released "official" photos of dogs Pchelka (top) and Mushka launched aboard the Third Spacecraft Satellite. Credit: Roskosmos


Several decades after it was used for tracking early launches, the Kama relay antenna stands as a monument at Site 18 in Baikonur. Copyright © 2001 Anatoly Zak








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