The USSR sends a probe 4,400 kilometers up

On Oct. 12, 1967, the USSR launched a unique experiment to study the near Earth's space. A rocket topped with an acorn-shaped probe called VKZ shot straight up to an altitude of 4,400 kilometers before plunging back to Earth while taking highly precise measurements of our planet's ionosphere.


The VKZ mission at a glance:

Launch date
1967 Oct. 12
Maximum altitude reached
4,400 kilometers
Spacecraft mass
310 kilograms
Scientific payload mass
35 kilograms
Time of operation
52 minutes (3,120 seconds)
Launch vehicle
Launch site
Tyuratam, Site 41, Pad 15


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Probing the ionosphere

The Vertical Space Probe, or Vertikalny Kosmichesky Zond, VKZ, became one of the first Soviet efforts in the early Space Age designed to understand the ionosphere, which in 1967, was still a relatively little known region of the near-Earth's space beginning at an altitude of 50 kilometers and extending as high as 25,000 kilometers.

Because the ionosphere reflects radio waves and changes their properties, its study had wide-ranging implications for many practical fields of science and technology.

In the VKZ experiment, the USSR's Academy of Sciences hoped to draw a vertical profile for the distribution of atomic and molecular ions in the upper atmosphere and precisely measure the intensity of cosmic particles at various altitudes. The experiment also aimed to measure levels of radiation in near Earth's space and test several types of anti-radiation shielding at altitudes between 3,000 and 4,000 kilometers. Finally, the VKZ probe was designed to measure the density of neutral atomic hydrogen in the region.

Instead of launching a traditional sounding rocket, the authors of the VKZ experiment wanted to separate the capsule with instruments from the main rocket in order to keep their measurements super pristine. Most of the studies planned for the project would be conducted for the first time and expected to play an important role in the planning of future space flight and the development of space technology.

VKZ design

The Academy of Sciences assigned the development of the VKZ probe to the KB PM design bureau (today ISS Reshetnev) based in the Siberian city of Zheleznogorsk. It became the first purely scientific vehicle for this organization, which until then had specialized in military and civilian application satellites. Inside KB PM, Department 32 took charge of the overall design, with young engineer Aleksandr Barinov coordinating the entire project and engineers Rafael Rabinovich and Viktor Martazov playing leading roles. Department 30 developed the new power supply system for the probe.

The 310-kilogram VKZ probe was designed as a pressurized container holding the scientific instruments and all the supporting gear, which included the gyroscopic stabilization system, the trajectory measuring system, the radio and telemetry-transmission system, the timer/programming sequencer and the device for automated control of the onboard equipment during the flight. On its exterior, the probe carried sensors for the scientific instruments, attitude control sensors and radio antennas.

Because the sensitive scientific instruments of the VKZ probe had very strict requirements against interference and contamination, the spacecraft could not be ejected from the rocket in the traditional way using pyrotechnics. Instead, Department 4 at KB PM developed a brand new spring-loaded separation mechanism which was guaranteed not to contaminate ongoing measurements and designed to exert minimum disturbances on the motion of the probe. In the meantime, Department 31 led by Vladimir Bartenev programmed the second stage of the rocket to turn and fire its thrusters immediately after the separation to significantly increase its distance from the probe, also to minimize its interference with sensitive measurements.

For the same reason, the VKZ vehicle was built out of materials which minimized gaseous emissions during the flight.

VKZ lifts off

When the rocket with the VKZ probe under its payload fairing had already rolled out to the launch pad, engineers going through the processing log discovered a signature meant to confirm the removal of a protective cover from one of the sensors was missing. If the cover really remained on the spacecraft, it would render the launch useless. Barinov and Deputy Designer General for Testing Anatoly Ushakov climbed to the top of the vehicle on the pad, where Barinov stuck his upper torso into a small hatch in the fairing, while Ushakov held him by his feet. Balancing in this difficult (and probably dangerous) position, Barinov was able to reach the instrument in question and confirm that the cover had indeed been removed. At the same time, he noticed a flaw in the attachment of the capsule's thermal blankets, which he was able to fix in place. (819)

An 11K65 (Kosmos-3) rocket carrying the VKZ probe lifted off from Site 41 in Tyuratam on Oct. 12, 1967. Unlike traditional launches, which begin arching toward the horizon after a short vertical ascent, the VKZ vehicle continued climbing almost vertically until the separation of the spacecraft. At that point, its trajectory reached only an 88-degree angle toward a local horizon.

The scientific payload of the probe was activated shortly before it separated from the second stage of the launch vehicle. The VKZ then continued a passive ascent up to an altitude of 4,400 kilometers before the Earth's gravity pulled it back.

During a 52-minute flight, the VKZ was recording data during both the ascent and descent phases of the flight. The vehicle transmitted its data to ground stations before it plunged back into the Earth's atmosphere and burned up.

The scientific data from the VKZ mission is known to have gone to several Soviet research centers:

  • Moscow and Irkutsk divisions of Institute for Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, IZMIRAN;
  • The Cosmo-physical Studies and Aeronomy Institute within the Yakutsk Branch of the Siberian Section of the Academy of Sciences;
  • The Nuclear Physics Institute of the Moscow State University, MGU. (818, 819)

Second VKZ launch

Another copy of the VKZ probe was launched from the same pad in Tyuratam on the follow-on Kosmos-3 rocket on March 28, 1968, and apparently went as scheduled.


Because the VKZ program was considered purely scientific, the Ministry of General Machine-building, MOM, made the decision to declassify the probe and bring its copy to the Paris Air and Space Show in Le Bourget in 1969. The probe was also displayed at the Kosmos Pavilion within the Exhibit of Economic Achievements, VDNKhA, in Moscow, the most high-profile exhibit venue in the former USSR. (819)


The article and photography: Anatoly Zak; Last update: August 29, 2023

Page editor: Alain Chabot; Last edit: October 21, 2017

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insider content



The flight profile for the VKZ probe.


A Soviet-era photo of the VKZ probe.


The VKZ probe during assembly at NPO PM in Zheleznogorsk, USSR, around 1967. Credit: ISS Reshetnev


A Kosmos-3 rocket on the launch pad in Tyuratam. Credit: PO Polyot


During the Soviet period, a full-scale replica of the VKZ probe was displayed at the VDNKhA exhibit in Moscow. Credit: ISS Reshetnev


A replica of the VKZ probe. Credit: ISS Reshetnev