As ESA astronaut Andreas Mogensen, Aidyn Aimbetov and Gennady Padalka prepare for undocking inside their Soyuz TMA-16M spacecraft, the remaining six astronauts on the International Space Station have a task too.
They are instructed to photograph the departing Soyuz when it leaves and pay particular attention to the rubber docking rings that ensure a tight seal.
In 2001 the Progress M1-7 unmanned cargo vessel had problems docking with the International Space Station. It was later revealed that the previous Progress, M-45, to use the same docking port had left behind one of the rubber O-rings, hampering the docking of the new arrival. A spacewalk was necessary to remove the old O-ring.
Since this incident, whenever a Soyuz or Progress leaves the Station astronauts take pictures to send to ground control for checking that everything is in order.
The crew must use an 80-400 mm lens and set the camera settings to ISO 400, highest quality, F5.6 and shoot from the Zvezda Service Module 26. Before taking the pictures they must turn off the interior light. The Soyuz flood light will be turned on and must not be in the frame.
Once finished the photos are downloaded to Moscow Mission Control for checking.