MOSCOW, November 17. /TASS/. The Russian crew of the International Space Station will be increased from two to three no sooner than the spring of 2018 after a multifunctional laboratory module Nauka (Science) enters service, Roscosmos Executive Director for Manned Space Programs Sergei Krikalyov told TASS on Thursday.

It was earlier reported that the number of Russian cosmonauts working aboard the world’s sole orbiter would be reduced from three to two starting from the spring of 2017.

"The State Commission has approved the switchover to two persons before the multifunctional laboratory module enters service," he said.

The module Nauka is planned to be launched in December 2017, he added.

"After its launch, some more time will be needed for its integration into the Russian segment of the International Space Station. As soon as the multifunctional laboratory module is docked to the space station and its integration begins, a large number of outer space walks will be required. By that time, we plan to increase the Russian space crew to three members again. This will approximately take place in March 2018," Krikalyov said.

Roscosmos may sell a vacant seat aboard a Soyuz spacecraft to space tourists or representatives of foreign space agencies, Krikalyov said.

Roscosmos earlier decided to reduce the number of Russian cosmonauts working aboard the space station from three to two from the spring of 2017. Owing to this decision, a vacant seat has appeared in two Soyuz spaceships scheduled for flights next year.

"We’re considering various options: a brief tourist flight, an astronaut’s lengthy flight or cargo delivery. It is not ruled out that there will be some vacant seats," he said.

As was reported earlier, a new space tourist may fly to the International Space Station in September next year. He may spend about 10 days aboard the world’s sole orbiter.

By now, seven space tourists have performed space flights. One of them did this twice. All of them made orbital flights aboard Russia’s Soyuz spacecraft.