A SECRET Nasa report concluded that Mars missions should not be undertaken by a mixed gender crew due to the risk of male and female astronauts getting frisky, the British astronaut Helen Sharman has claimed.

The journey to Mars and back would take up to a year, exposing brave cosmic travellers to huge blasts of potentially lethal radiation.

2 Could astronauts ROMP while on the way to Mars? Credit: AP:Associated Press

2 Helen Sharman was the first British person to go to space and travelled to the Mir space station in 1991 Credit: Getty Images - Getty

But if men and women were both aboard the spaceship, they would be highly likely to float into bed together due to humans' inescapable desire to romp with anyone they spend a lot of time with.

Speaking at the New Scientist Live festival this morning, Helen Sharman suggested there was an official study surrounding "impure thoughts" during a Mars mission which had never been published.

Sharman, who was the first Brit to go into space, said: "I did hear some years ago that there was a report.

"Nasa has never released it, but it was done to see exactly the kind of crew makeup was necessary for the reason we have already alluded to.

"It found that the crew should be the same gender: all men or all women."

It's unclear exactly consequences of sex in space might be.

Perhaps there are fears women could end up pregnant, which would lead to the nightmare scenario of having to give birth aboard a spaceship.

Arguments could also erupt between lovers or they could become jealous of other crew members who have spurned their affections.

But Sharman told an audience at the Excel Centre in London that Nasa concluded an all-female crew would be the best bet, as women were "more collaborative" and men squabbled over who was "the leader".

Astronaut Al Worden, the pilot of the Apollo 15 who flew to the moon in 1971, also told the audience that he was the best person to go to Mars because, at the ripe old age of 85, he's not as frisky as he used to be.

Worden said: "If I was 29 instead of 85 I would probably have thoughts that are impure.

"When you get to be 85, you still have those thoughts but you can't do anything about them, so I would be just fine going to Mars and back."

While the idea of humans Mars might seem like a long way off, Tesla and Space X billionaire Elon Musk has boasted that he will put a colony on the red planet by 2030.

Nasa recently conducted a mock Mars mission on a volcano in Hawaii.

Six researchers spent eight months in a secluded dome to better understand how humans would behave in Martian conditions.

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