How do astronauts train for space?
Rosemary Coogan could be the first British astronaut to one day walk on the Moon.
Rosemary graduated from a special training programme last year, becoming the UK's third-ever astronaut.
The European Space Agency (ESA) is hoping to send Rosemary to the International Space Station (ISS) by 2030.
To prepare, she's taken part in spacewalk training lasting six hours. She's lowered, in full astronaut kit, into a 12m pool containing a life-sized replica of the space station.
The pool has the same feeling of weightlessness in space.
BBC News Science Editor Rebecca Morelle went to meet Rosemary during the training at Nasa's Johnson Space Centre in Houston, Texas.