ESA astronaut Thomas Pesquet waves as he descends to a mockup of the International Space Station at NASA's Neutral Buoyancy Laboratory in Houston, USA.

Training underwater is as close as it gets to experiencing weightlessness on Earth so spending time in a full spacesuit is used to practise techniques for spacewalks.

The training pool is the largest indoor swimming pool in the world, holding over 23 million litres of water, but it is still not large enough to hold the complete Space Station. Instead, specific parts of the Station structure are used as needed for training.

Support and training divers are on hand to guide the astronauts during their tasks. In space, the astronauts are aided by mission control and colleague astronauts on the Station.

A typical training session lasts up to six hours confined in the spacesuit 12 m underwater.

Thomas conducted this spacewalk training with colleague ESA astronaut Andreas Mogensen, both members of ESA's class of 2009 astronauts. Watch the slideshow below for more photos and follow their training on their own blog through the link to the right.