Soyuz 23 was launched October 14, 1976 and was meant to be the second mission to Salyut 5. After the rendzevous system failed once again, the mission had to be aborted and the crew ended up landing in a frozen lake and being submerged for a night.

On board were Valeri Rozhdestvensky and Vyacheslav Zudov. Their callsign for the mission was Radon (Radon).

The mission was completely nominal up until the point when the crew were 40 metres from the station. At this point the Mission Control noticed that the spacecraft was approaching too fast and at the wrong orientation. They therefore overid the automatic system and stop the approach. At this point the crew were on the night side of the Earth and mission rules forbid a docking at night.

The commander, Zudov asked whether he could try a manual docking. This request was denied because another mission rule stated that rookie commanders could not attempt manual dockings. The other factor that came into the decision was that the crew had not spent that much time training in the Soyuz spacecraft. They had enough to fly a nominal mission and various standard problems but had spent much of their training time on the Salyut space station.

It was decided to return the crew to Earth. The retrofire was nominal and the crew were set to land in the standard area. But Mission Control did not send enough commands to the orientation engines meaning that the descent path deviated too much from the standard. This failure came from a mistake in the calculations performed to work out the reentry procedures. Another factor in the off target landing was the very windy conditions that blew the capsule off course even more.

What wasn't realised was the crew were heading for a the frozen Lake Tengiz, 195 km southwest of Tselinograd, Kazakhstan. The standard procedure called for a valve to open at 5 km to equalise the pressure and for the crew not to jettison the parachute on landing. So when the spacecraft landed it broke through the ice crust and went under. The parachute became wet and dragged the capsule underwater and upside down. The valve started to let water into the capsule. The crew quickly closed it when they realised what was happening.

Zudov later said:

"...We had no possibility to get out of the capsule, as we did it before and as we were taught. If we open the hatch, and it was under water, the stream will come onto the cosmonauts, and there would be no chance to get out. Besides – very low temperature on water. Temperature on Lake Tengiz was minus 22°C. To stay in such situation in the spacesuits and do nothing – we would be frozen and die. That's why first we had to do – to get out of spacesuits and to free ourselves of them. We spent an hour and a half to get out, even used knives to cut them. Then we managed to wear our plain sport wear. Started to save electric power. Switched off all sources inside the capsule – left only radio beacon and radio station which we could use in due time – but it failed soon... ...Our work inside the capsule was, as it seems to me, more clearly to my mission engineer – at least he was a diver, submariner..."
The next problem facing the crew was that there was no way for fresh air to get into the capsule so they would have to use the regeneration equipment. This was not designed to operate for longer than a couple of hours. Rozhdestvensy worked out a way to save the equipment:
"...You could feel CO2 (carbon dioxide gas) without any instrumentation, just feel it. When I felt that it at the stage – which we could lose consciousness – then I switched on the regeneration unit. Then, when the mind started to clear, and blue halo we were starting to see disappeared in the eyes – I switched it off. And so on – all the night."
The shoreline of the lake was swampy preventing amphibious vehicles reaching the capsule that had landed 2 km from the shore. It was decided that the only way to rescue the crew was to hook the parachute up to a helicoptor and try to somehow dragged it too shore. This was accomplished by having a diver jump into the freezing lake and hook a line to the capsule. The helicoptor than dragged the capsule for over 5 km to solid land.