Soyuz TM-8 was a spacecraft used to launch and land the crew of the fitfh long duration crew to the Soviet Space Station Mir. It was part of the Soyuz TM-5 series of spacecraft, which were the fourth generation of the Soviet Soyuz. Soyuz TM-8 was the eighth manned spaceflight to Mir, and spent 166 days in orbit.

The Soyuz-U2 rocket was painted with advertisements. During the Soyuz Spacecraft's final approach to Mir (4 metre distance), the Kurs rendezvous and docking system malfunctioned, so Viktorenko took over manual control and withdrew to 20 metres, and then docked manually. The spacecraft spent 166 days attached to Mir, for the duration of the expedition Mir EO-5.

Soyuz TM-8 arrived at Mir after five months during which the station was uninhabited. The Kvant2 and Kristall modules were now ready for launch, and the station began its second period of expansion. On September 29, 1989 the cosmonauts installed equipment in the docking system in preparation for the arrival of Kvant2, the first of Mir's 20-ton add-on modules. Solar storm warnings reached the cosmonauts. On September 30, 1989 a powerful flare burst out on the Sun. Initial predictions indicated that the cosmonauts could receive many times the maximum permissible level of radiation. In the event, the cosmonauts received only about as much radiation as they would normally receive in two weeks of flight.

It was announced on October 10, 1989 that problems with a batch of computer chips pushed back the launch of Mir's second add-on module by at least 40 days from the planned October 16, 1989 launch date. The major focus of Aleksandr Viktorenko and Aleksandr Serebrov's mission was to receive, check out, and activate the module, so their schedule underwent heavy revision.

On December 12, 1989 the crew flew Soyuz TM-8 from the aft port of Mir and docked to the forward port now cleared of the Kvant2 module. Progress M-2 arrived at Mir and remained docked to the aft port from December 22, 1989 - February 09, 1990.

The new guidance control computer for Mir, the Salyut 5B system delivered by Kvant2, needed star sensors more capable than those in place on Kvant.

The cosmonauts performed the first EVA on January 08, 1990 (2h 56m). Aleksandr Viktorenko and Aleksandr Serebrov opened one of the three free docking node hatches, transferred the twin 80-kg sensor packages outside, and installed them on Kvant. The start of the EVA was delayed 1 hour by a depressurization problem in Soyuz TM-8 when the cosmonauts lowered pressure in the docking node, an improperly set valve released air from the spacecraft as well.