Soyuz 18 was launched May 24, 1975
. It was the second time that the Russians had tried to launch Soyuz 18, with the first
ending in a high altitude abort
. The actual Soyuz 18 was the second mission to the Salyut 4
space station, this time for 2 months. The mission ran concurrently with the ASTP
flight, though this had not been planned.
On board were Pyotr Klimuk and Vitali Sevastyanov. Their callsign for the mission was Kavkas (Caucasus).
Salyut 4 was a civilian space station and as such was similar to the American Skylab in the experiments performed. It was primarly an astrophysical observatory and as such 4 telescopes. OST-1 was used for observing the sun in ultraviolet in order to measure its surface temperature. ITS-K was a infrared telescope the studied bright stellar, galatic and solar systems objects. Filin was used in the new field of X-Ray astronomy. These high energy waves cannot penetrate the Earth's atmosphere and so have to be observed from Earth orbit. And finally, RT-4 was a second X-Ray telescope used to measure the 'brightness' of objects.
As well as their astrophysical research, the crew also did biological experiments. There were various closed containers that investigated single celled plant growth, fruit flies, development of eggs of the South African Marsh Frog and changes in animal cell structure. Their was also the Oasis-1M greenhouse that grew several types of plants to see how well they grew in microgravity, principally onion and pea plants.
There was some concern from quarters in the US Congress. These mainly centered around the fact that this mission overlapped with the time when the Apollo and Soyuz spacecraft would be in space for the ASTP. The Soviets assured the Americans that in the case that Salyut 4 and Soyuz 19 were passing over the same tracking station at the same time then Soyuz 19 would be given priority (the chances of this happening were calculated to be minimal by the Americans and if it did in fact occur they would only be over the same tracking station for a maximum of a minute and a half). And the mission control for Soyuz 18/Salyut 4 would be done from the site that had been used prior to Soyuz 12. Soyuz 19's control would be in Kaliningrad.
The capsule landed 56 km north of Arkalyk, Kazakhstan.