The third law of motion may not be the most romantic starting point for sex in space. It is, however, crucial.

The law states that "every action has an equal and opposite reaction," and on Earth that's fine. Two people moving away from each other can rely on gravity to stop them flying across the room, but in a weightless environment that would be a problem.

As a way to overcome it, Vanna Bonta – writer, actress, sci-fi poetess and space enthusiast – developed 2suit, a two-seater space suit that will zip two astronaut lovers inside.

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Vanna came up with the idea in 2006, on a zero-gravity flight arranged by the National Space Society, but didn't test the suit until September 13, 2008. Its inaugural outing was on board the G-Force One, the so-called Vomit Comet that simulates zero-gravity by swooping up and down through the atmosphere.

During trials, the History Channel filmed the first weightless kiss for its documentary. Vanna spoke of the suit, rather disconcertingly, in both romantic and practical terms.

“The feeling of no attraction between two masses impressed me," she said. "Once you attached the suit two people can be inside of it, like a large bag, and have some privacy. Also it can be useful in emergency situations as it can store body heat.

“At first we found it impossible to kiss, but the 2suit stabilised us,” she added. “In two years’ time people could go on their honeymoon in space, but this needs to be done responsibly as there is an issue of pregnancy.”

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As Vanna suggests, contraception would be essential. Experiments conducted with rats on board of the Space Shuttle revealed that embryos developed abnormally in zero-gravity conditions. It's believed that the concentration of radioactive particles inside the shuttle may affect cell replication in a similar way to cancer.

According to Vanna, the documentary was the first step towards open discussion of the issue of sex in space. Embarrassment or prudishness has stifled official debate, although on the scientific side, Nasa researchers have been investigating human biology in extreme conditions, including weightlessness. Jim Logan from Nasa Space Medicine Associates has said that reproductive biology would encounter serious problems in space, if humans ever decided to switch to a zero-gravity civilisation.

Opinion is divided about whether pioneer space-lovers would be able to get that far. The History Channel documentary looked at the issue of libido and virility in orbit and concluded that the space experience might have a “Viagra effect”, since blood would flow more easily in zero-gravity conditions. Other researchers, however, have suggested that the reduced testosterone levels, muscular mass and bone density associated with space travel would dampen sexual desire.