Rats have flown to space before but the new "rat-stronauts" will stay between 30 and 90 days, depending on the how soon they can get transported on the roundtrip, space.com reported.
"This will allow animals to be studied for longer period of time on space station missions," said Julie Robinson, chief scientist for the International Space Station (ISS).
Of the 35 or so studies where rats have gone into space, few have gone for more than two weeks.
Robinson said that launching rats on for the experiment are preferable to mice, which are smaller and require less food, because rats' neurocognitive functioning is similar to that of humans.
Investigators are pushing for more life sciences experiments on the ISS to better understand the effects of microgravity on living organisms.