The freeze-dried sperm samples were launched to the ISS in 2013 and returned to Earth the year after.

The intense radiation of space caused slight DNA damage to the sperm, but after in-vitro fertilisation on the ground, healthy offspring resulted. The baby mice grew into adults with normal fertility of their own.

The researchers – led by Sayaka Wakayama of the University of Yamanashi – said it is a step towards reproducing other mammals, even humans, using space-preserved sperm.

They envision missions lasting several years or multiple generations, during which assisted reproductive technology might be used for domestic animals and people.

The findings were published in the Proceedings of the National Academy of Sciences.

The ISS orbiting the Earth

Previous developmental studies in space have involved, among other things, fish and amphibians.

Mammals are more difficult to maintain and handle in space so testing has been limited. More extensive testing on sperm preservation is needed in space, according to the researchers.

Besides looking ahead to long-term space crews and societies, the researchers see other reasons for saving sperm in space, including in the event of disasters on Earth.

The moon would be ideal for underground sperm storage, they said, in particular lunar lava tubes because of “their very low temperatures, protection from space radiation by thick bedrock layers, and complete isolation from any disasters on Earth”.

Earlier this month, a planned spacewalk outside the ISS was cut short after a cable supplying power, oxygen, cooling water and communications to a spacesuit developed a leak.