ESA ATV Albert Einstein: Fully fuelled at Europe's Spaceport in Kourou, French Guiana

ATV Albert Einstein is fuelled at Europe's Spaceport in Kourou, French Guiana. 

Automated Transfer Vehicles (ATVs) carry two types of propellant to the International Space Station. 

Aside from its own propellants, the space ferry brings propellants for the Russian Station thrusters. 

They are loaded in four phases - and each component is highly toxic. 

All non-essential personnel are cleared from the room and operators wear sealed 'scape suits' at all times during fuelling. 

Image courtesy ESA/CNES/Arianespace/Optique Video du CSG.

Automated Transfer Vehicles (ATVs) can deliver up to 7 tonnes of cargo to the International Space Station, including supplies and equipment, water, air, nitrogen, oxygen and fuel.

As the Space Station circles Earth, it slowly loses altitude so ATVs reboost the orbit to keep it aloft.

Part of ATV's cargo includes propellants for the Station's own thrusters to keep the orbital outpost at the right height even when no spacecraft are there to offer a helping hand.

Loading the fuel is a complex and hazardous process that takes place over many days during continuous sessions of up to 30 hours.

Should there be a leak, the operators are protected by 'scape suits' that deliver fresh air and are sealed off from the working environment, much like diving suits.

The operators must remain vigilant at all times, constantly checking progress and signs of leaks. To make matters more complicated, ATV own propellants are different to those used by the International Space Station itself, requiring different equipment each time.

Both fuels need separate oxidisers for combustion outside of Earth's atmosphere. The oxidisers are also loaded separately, meaning that four different liquids are being pumped into Albert Einstein's tanks in total.