In May 1986, Leonid Kizim and Vladimir Solovyov left the newly opened Mir, crossed 2,500 kilometres to Salyut 7, and returned carrying 350 to 400 kilograms of instruments — the only human voyage ever made from one space station to another

On 5 May 1986, Leonid Kizim and Vladimir Solovyov sealed the hatch of the newest space station in orbit, climbed into Soyuz T-15 and pushed away from Mir with another station waiting roughly 2,500 kilometres ahead.

Twenty-nine hours later, they docked with Salyut 7. They would spend 50 days there, carry out two spacewalks, remove 20 instruments weighing between 350 and 400 kilograms, and then fly back to Mir. According to NASA’s Mir Hardware Heritage, it remains the only crewed flight ever made from one space station to another.

One station was beginning while the other was nearing its end

Mir’s core module had reached orbit only a few weeks earlier, in February 1986. It was the beginning of what would become the first modular space station, gradually enlarged with laboratories and living compartments over the following decade. The European Space Agency’s history of Mir describes the station as a bridge between the earlier Salyut outposts and the much larger International Space Station that followed.

Kizim and Solovyov launched from Baikonur aboard Soyuz T-15 on 13 March and reached Mir two days later. They were the first crew to enter the new station.

Even that first docking required an unusual maneuver. Soyuz T-15 carried the older Igla rendezvous system, which was compatible with Mir’s aft port, while planners wanted to keep that port open for arriving Progress cargo vehicles. After approaching from behind, the cosmonauts shut down the automatic system and manually flew around Mir to dock at its forward port.

For the next seven weeks, the two men activated systems, checked equipment and unloaded the Progress 25 and Progress 26 supply ships. Mir was still only its cylindrical core, without the scientific modules that would later give the station its sprawling, asymmetrical shape.

The crew already knew Salyut 7 by touch

Salyut 7 belonged to an older generation. Launched in April 1982, it had served as the Soviet Union’s main orbital laboratory through a succession of long expeditions, visiting crews and cargo flights.

Kizim and Solovyov were unusually suited to return there. Along with physician Oleg Atkov, they had lived aboard Salyut 7 for 237 days in 1984. When they left on 2 October of that year, they had spent nearly eight months operating its controls, experiments and life-support systems.

The station did suffer a severe power and communications failure in early 1985. Vladimir Dzhanibekov and Viktor Savinykh reached it aboard Soyuz T-13 that June and carried out one of the most difficult repair missions in spaceflight history, restoring power and making the interior habitable again.

But Kizim and Solovyov were not returning to a frozen, tumbling wreck. Salyut 7 had been repaired and occupied again before its final resident crew returned to Earth in November 1985. What remained aboard was unfinished experimental work and equipment that could still be useful on Mir.

The two stations had been placed in compatible orbits

The transfer was possible because Mir and Salyut 7 travelled around Earth at the same orbital inclination of approximately 51.6 degrees. Salyut 7 was in a somewhat lower orbit and several thousand kilometres ahead of Mir along the same general track.

On 4 May, controllers lowered Mir’s orbit by approximately 13 kilometres. The maneuver helped the new station begin closing the distance and reduced the amount of propellant Soyuz T-15 would need to complete the rendezvous.

By the time Kizim and Solovyov undocked on 5 May, the separation had fallen from roughly 4,000 kilometres to about 2,500. A surviving NASA history, also available as a public transcription of the original report, records the transfer as a carefully staged orbital chase rather than a direct flight across a fixed gap.

Soyuz T-15 spent 29 hours in free flight. Kizim and Solovyov docked with Salyut 7 on 6 May, becoming the first people to arrive at a space station after departing from another one.

They spent 50 days finishing work left aboard Salyut 7

The station had been unoccupied for about five and a half months. Once aboard, the cosmonauts reactivated the systems they needed and resumed experiments that the previous expedition had been unable to complete.

Their work included material-science investigations, the retrieval of samples exposed to space and tests involving the large Kosmos 1686 module docked to the station. The Soyuz T-15 mission record lists the Salyut visit as the middle portion of a 125-day flight that began and ended at Mir.

On 28 May, Kizim and Solovyov went outside for three hours and 50 minutes. They retrieved exposure experiments and tested the Ferma-Postroital device, which unfolded a compact cartridge into a metal girder approximately 15 metres long.

They performed a second spacewalk on 31 May. During five hours outside the station, they extended the girder again, attached measuring equipment and used an electron-beam tool to weld several of its joints. The tests explored ways of assembling larger structures in orbit, although the article’s earlier claim of a direct engineering line from this experiment to every later space-station truss went beyond the available evidence.

They carried as much as 400 kilograms back to Mir

Before leaving, Kizim and Solovyov removed 20 instruments and packages from Salyut 7. NASA’s mission history puts their combined mass at approximately 350 to 400 kilograms.

The cargo included experimental apparatus, material samples and scientific instruments, among them a multichannel spectrometer. The equipment was transferred into Soyuz T-15 for the return journey rather than left aboard a station approaching the end of its useful life.

Controllers adjusted Mir’s orbit again on 24 and 25 June to reduce the work required of the Soyuz. Kizim and Solovyov undocked from Salyut 7 on 25 June, leaving the station without a crew for the final time.

The return crossing lasted another 29 hours. Soyuz T-15 redocked with Mir on 26 June, completing a round trip between two separate orbital stations.

The cosmonauts spent another 20 days aboard Mir before returning to Earth on 16 July. Their mission lasted 125 days and closed the operational history of Salyut 7 while opening Mir’s. A later generation of crews would push endurance far further, including Valeri Polyakov’s 437 consecutive days aboard Mir.

The flight has never been repeated

The maneuver was not impossible because the stations happened to be thousands of kilometres apart. Spacecraft routinely close much larger distances while circling Earth. What mattered was that Mir and Salyut 7 shared the same orbital inclination, that both could accept the same Soyuz ferry and that planners had deliberately moved the stations closer before each crossing.

Those conditions have not lined up again for a human crew. Later stations have generally operated alone or in orbital planes that would make a transfer prohibitively expensive in propellant. Soyuz T-15 therefore remains the only mission whose crew entered one space station, flew to a second and then returned to the first.

Salyut 7 was raised to a higher orbit after the cosmonauts left, but it eventually re-entered uncontrollably over South America on 7 February 1991, scattering fragments across parts of Argentina. Mir survived another decade before controllers sent it into the Pacific in March 2001, an ending Space Daily has covered in detail.

Both stations are gone now. What remains is the path Soyuz T-15 traced between them: 29 hours outward, 50 days attached to the older station, 29 hours back, and up to 400 kilograms of instruments arriving inside a Mir that had been empty when the crew returned.