New study finds microgravity disrupts sperm and embryo development, raising concerns about human reproduction in space.

As a quartet of astronauts make their way to the far side of the Moon, far-fetched notions of human colonies on the satellite or even Mars - a three-year return trip - are again getting an airing.

Humans living in space for months, years, or even generations will need to navigate sex in a zero-gravity world.