Litters of healthy mice — “space pups” — prove that mouse sperm can be freeze-dried, flown around on the International Space Station for nine months and then used to make babies, researchers from Japan are reporting in Proceedings of the National Academy of Sciences.

Why do such a thing? At an altitude of 250 miles, where the station orbits, radiation is more than 100 times stronger than on earth. The scientists, from the University of Yamanashi, wanted to find out if prolonged exposure would affect fertility or the health of any offspring. They are looking ahead to a time when humans spend years in space habitats and might want to use frozen sperm and eggs up there.

Much like the orange-flavored Tang that astronauts used to drink, freeze-dried mouse sperm can be reconstituted with water. Although tests on the space sperm did find slightly increased DNA damage, compared with freeze-dried earth sperm, the space version did the job when it came to fertilizing eggs.

Birthrates and male-to-female ratios were normal, and the space pups went on to have healthy pups of their own. Apparently, after fertilization, nature somehow fixed the DNA damage.