Later this month the International Space Station's partners will formally agree the arrangement for the transport and emergency return of the station's crew when it doubles in size to six from May next year.
Already agreed informally, two Rocket and Space Corporation Energia -built Soyuz spacecraft will transport two crews of three to the station, one launching in April and then one in May.
The April crew will return to Earth in October, reducing the ISS complement to three, but two weeks after their landing the launch of a third three-person crew will take place, bringing the station team back to full strength.
Then in November the second team of three, launched in May, will depart, leaving that October team behind and again reducing the ISS to three members. But two weeks later a fourth team will be launched to return the ISS to full strength again. This cycle will continue until the station ends its operational life.
Speaking at the European Space Agency's launch of its next round of astronaut selection on 8 May, ESA's ISS programme manager, Alan Thirkettle, says: "There is no reason why the station can't continue until well into the 2020s."