While rodents have flown on space shuttle flights in the past, those missions have only lasted a week or two. This new rats in space mission, however, could range between 30 and 90 days, depending on the availability of spacecraft like SpaceX's Dragon capsule to ferry them on the roundtrip.

This means there will need to be changes to animal husbandry to keep the rats happy and healthy, said Julie Robinson, NASA's chief scientist for the space station, in a recent press conference.

"This will allow animals to be studied for longer period of time on space station missions," she said, adding that of the 35 or so studies where rats have gone into space, few of them have gone for more than two weeks.