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As British astronaut Tim Peake gets his Earth legs back after his recent return from six months aboard the International Space Station, one of his European Space Agency astronaut corps colleagues is training for a second stint in orbit – which will include an unusual responsibility.

Germany’s Alexander Gerst, who spent six months on the ISS in 2014, was earlier this spring selected for a second mission, in 2018, during which he will spend three months in command of the ISS – just the second time a European will have been in charge of the outpost.

The first European to hold that role was Frank De Winne, in 2009. De Winne – a distinguished flyer, brigadier general in the Belgian air force and now head of the European Astronaut Centre – tells Flightglobal that while a space station crew are all highly trained and extraordinarily competent, the commander has some specific – and critical – duties. In training on the ground and in orbit, commanders are responsible for crew cohesion, ensuring they work together as an integrated unit, and are the crew’s spokesperson in communications with the operations team.

“You can be more effective if you have a good crew than if you have good individuals,” says De Winne.

In orbit, day-to-day activities are co-ordinated by the flight director on the ground, but if there is any sort of unusual event that cannot be directed from the ground, the commander has to take charge. Depending on the orbital position, it is not unusual to have up to 15-30mins of interruption of communication with the ground, but as there are many redundant systems onboard it would be highly unusual for comms to be lost for any significant period of time. However, there can be unusual, emergency events that for practical reasons would have to be handled onboard, and the commander would step into action: fire, a toxic atmosphere incident or depressurisation. “You don’t want to improvise in these cases,” says De Winne. Priorities, then, are the safety of the crew, the safety of the station and, lastly, the success of the mission.

Generally, good commanders have experience in space and a “very co-operative communication style”, he says. They must show leadership, to bring the crew together, and also followership, to ensure that all crew members are fully engaged during the mission.

And, they are the principal team member in communications with the ground, so must be good at communicating quickly and clearly with people of different backgrounds – and maybe under difficult technical conditions, for example while wearing oxygen masks during an emergency. Historically, many astronauts have been military pilots, in part because their communication skills are well-honed to the task. But military backgrounds are not exclusively ideal; Gerst is a civilian, a scientist.

That last point highlights one of the big challenges of commanding the ISS. As De Winne observes, it is one thing to be a good leader among peers – but much harder to lead a diverse crew. The “I” in ISS stands, after all, for “international”.