The Neutral Buoyancy Facility (NBF) at ESA’s Astronaut Centre (EAC) in Cologne, Germany is 10 m deep and holds 3.7 million litres of water. It is used to train astronauts for spacewalks and test prototypes for new lunar tools.

Built by the German Aerospace Centre DLR in 1990, it was last refurbished in 2007 in preparation for the 2009 astronaut selection and their initial spacewalk training at EAC. Now, it is getting a new lease on life, ready to support astronaut operations for the next 10-15 years.

The NBF refurbishment will take nine months to complete. This clip shows the water tank being emptied in preparation for this refurbishment – a process that takes seven days.

Refurbishing the NBF mainly involves removing the tank’s coating, repairing any damage or corrosion, refreshing concrete areas and reapplying the protective coating. The signs and labels on the walls have to be repainted and the underwater light system renovated. The challenge is to ensure that no piece of debris blocks the water circulation system and that the deck, training equipment and air circulation system is not contaminated by dust.

Once the refurbishment is complete, 3.7 million litres of water will be pumped back in over three weeks and reheated to 28°C. Diving activities are expected to resume in spring 2021.