supplies to the EO-4 crew, and remained docked to the station for 42 days. During this time, Progress 39 was used to boost the orbit of the space station. This was necessary due to the greater than normal atmospheric drag. The extra drag was caused by atmospheric expansion, which in turn was caused by the solar maximum occurring at the time, during solar cycle 22. The boost changed the Perigee and Apogee of the station from 325 km and 353 km AMSL to 340 km and 376 km, respectively. After the boost, Krikalev reported that he was unable to visually detect the change in altitude. The EO-4 crew filled Progress 39 with waste and excess equipment used during the Aragatz mission, and then the spacecraft undocked on February 7, and was intentionally destroyed during atmospheric reentry later that day. Progress 40 On February 10, the next resupply spacecraft, Progress 40 was launched, and it docked with Mir two days later. It remained docked to Mir for 18 days. During this time, it was announced that due to delays in the production of the Kristall module, the launch of the next Mir module, Kvant-2, would also be delayed. It was also announced that as a result, Mir would be left unmanned following EO-4. Progress 41 The final Progress resupply spacecraft of the expedition docked with the station on March 19, and remained docked for 33 days. Progress 41 was the second last Progress spacecraft to use the original design (the last being Progress 42, which resupplied Mir EO-6 in 1990). The updated design would be called Progress-M, and its first flight would be Progress M-1 in August 1989, just prior to the arrival of the Mir EO-5 crew in September. Leaving Mir unmanned All three crew members left Mir on board Soyuz TM-7 on 27 April 1989, bringing EO-4 to an end. For Volkov and Krikalev the mission lasted for 151d 11h 08m and for Polyakov 240d 22h 34m. References Mir 1988 in the Soviet Union 1989 in the Soviet Union