Mir EO-4 (also called Principal Expedition 4) was the fourth long-duration expedition to the Soviet space station Mir. The expedition began in November 1988, when crew members Commander Aleksandr Volkov and Flight Engineer Sergei Krikalev arrived at the station via the spacecraft Soyuz TM-7. The third crew member of EO-4, Valeri Polyakov, was already aboard Mir, having arrived in August 1988 part way through the previous expedition, Mir EO-3. The expedition lasted for five months, and at its conclusion Mir was left unmanned until the launch of Mir EO-5 in September 1989. This ended a continuous habitation of the space station which began in February 1987, with the arrival of the crew of Mir EO-2. Background The previous long-duration expedition to Mir, EO-3, was intended to break the record for spaceflight duration of 326 days set by Yuri Romanenko during Mir EO-2. The physician Valeri Polyakov was sent to the station part way through EO-3 so that he could observe the cosmonauts at the end of their record duration flight. Polyakov then stayed aboard Mir to observe the EO-4 crew. Crew Volkov, the only crew member who had been to space before, had one previous spaceflight. It was a two-month mission in 1985 to the space station Salyut 7, launched by the spacecraft Soyuz T-14. This expedition, Salyut 7 EO-4, was intended to be 6 months long, but the Commander Vladimir Vasyutin became ill, and the mission was shortened, forcing the cosmonauts to leave the station unmanned. Volkov became father of the first ever second-generation cosmonaut, when his son Sergey Volkov became Commander of the International Space Station's Expedition 17 in 2008. This was Krikalev's first spaceflight, and he went on to have a further five missions to space. As of 2010 he holds the record for the longest cumulative time spent in space, at 803 days. His most recent spaceflight was in 2005, as Commander of the International Space Station's Expedition 11. Polyakov, a physician, arrived at the station part way through the previous expedition, Mir EO-3. He had never been in space before, but would later have one more spaceflight, which would span three Mir expeditions: EO-15, EO-16, and EO-17. His second spaceflight, launched on Soyuz TM-18 in January 1994, would last 437 days, and as of 2010, still holds the record for the longest ever spaceflight. Backup Crew Aleksandr Viktorenko (Commander) Aleksandr Serebrov (Flight Engineer) German Arzamazov