LONDON - The prospect of long-term space travel has led scientists to consider, increasingly seriously, the following conundrum: if travelling to a new home might take thousands of years, would humans be able to successfully procreate along the way?
The early indications from Nasa are not encouraging. Space, it seems, is simply not a good place to have sex.
According to a review by three scientists looking into the feasibility of colonising Mars, astronauts would be well advised to avoid getting pregnant because of the high levels of radiation that would bombard their bodies as they travelled through space.
Without effective shielding on spaceships, high-energy proton particles would probably sterilise any female fetus conceived in deep space and could have a profound effect on male fertility.
"The present shielding capabilities would probably preclude having a pregnancy transited to Mars," said radiation biophysicist Dr Tore Straume of Nasa's Ames Research Centre.
Until recently, sex had been a taboo subject for Nasa, which has a strict code of conduct stating that "relationships of trust" among astronauts are to be maintained at all times.
Only once has a husband and wife been on the same mission - Jan Davis and Mark Lee - and they have remained tight-lipped over whether they joined the 62-mile high club.