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"CHAPEA Mission One is a-go!"

Those were the words as the door closed behind four volunteers on Nasa's year-long mission to "Mars".

OK, so it's not actually the planet Mars! It's actually a simulator pod at Johnson Space Centre in Houston, Texas in the United States.

But the CHAPEA or "Crew Health and Performance Exploration Analog" mission sees four scientists and engineers live in a small space built to simulate life on Mars.

The volunteers are now living in a 1,700 square feet space, which is around the size of two average three bedroom homes, for the next 378 days.

While in there, they will conduct various experiments to measure the impact of life on Mars for possible future missions to the red planet.

The space is 3D printed and consists of four bedrooms, a dining/living area, a workspace with a vertical farm to grow things and a medical room.

They crew will be given a series of challenges that mirror those of a true Mars mission.

They will have to overcome equipment failure, communication delays and environmental stressors.

The aim of the mission is to measure the human impact of possible future Mars exploration trips.

The crew all took a moment to say a few words before entering the Mars Dune Alpha, with Nathan Jones, medical officer saying goodbye to his wife and children.

"I love you to the Moon - I'm sorry - to Mars and back!" he said.

The crew were heard cheering from behind the door after it was closed behind them.

Crew commander Kelly Haston said the "crew has worked so hard this month to get ready for this mission."

"It has been very special to be a part of such a tremendous group of scientists and specialists from a diverse set of backgrounds working together to bring CHAPEA 1, the first of three missions, to reality."