In the wake of the Soyuz 11 tragedy, the spacecraft was redesigned to accommodate two cosmonauts who would wear pressure suits at all times during launch, docking, undocking, and reentry.

Finally, the 7K-T, being intended purely as a space station ferry, had no solar panels, instead sporting two large whip antennas in their place.

Then on 2 September 1972, an attempted launch of a Zenit reconnaissance satellite failed to orbit due to a malfunction of the vernier engines on the Blok A stage.

The existing stock of Soyuz boosters had to be modified to prevent a recurrence of this failure mode on a crewed mission, which delayed the next test until almost a year later when Kosmos 573 launched on 15 June 1973 and spent two days in space.

This featured the ability to remote control the space station and a new parachute system and other still classified and unknown changes.