In 1979, Cosmos 1129 flew five female and two male rats for 18.5 days and allowed them to mate; no normal pregnancies resulted in flight, while a later ground study produced healthy litters

Spaceflight can take a serious toll on the body. Bones demineralize, muscles atrophy, fluids shift upwards, and even sleeping becomes a challenge since there is no gravity to hold you down. One unusual question researchers asked decades ago involved rats: could a mammal become pregnant and stay pregnant after mating in orbit?

In September 1979, five female and two male rats were flown aboard the Soviet biosatellite Cosmos 1129, which spent 18.5 days in orbit. The animals were initially kept apart by a partition, which was removed after five days so they could mingle and mate during the remainder of the flight. The experiment was designed to examine whether the rats could mate in orbit and whether pregnancy could begin during spaceflight. NASA records describe the mission as an attempt to breed the rats during flight, while US researchers also conducted related embryology experiments aboard Cosmos 1129. The flight did not result in successful pregnancies and offspring. The results prompted further investigation by NASA scientists Eric Sabelman, Peter Chetirkin, and Robin Howard in their study Simulated Spaceflight Effects on Mating and Pregnancy of Rats.

The experiment and how the researchers recreated the mission in the lab


In their report, the researchers describe a process by which they successfully recreated almost the entirety of the flight in their laboratory, replicating everything down to the noises, vibrations, and accelerations of a launch, the shocks experienced during re-entry, and even the diet that was served to the animals on the Soviet mission in space. The rats were kept in enclosed cages, modeled after those used in the flight, for the duration that had been specified in the real mission, and the partition separating the males from the females was removed after five days to allow mating to happen just as it was planned to occur in space. Some groups were subjected to simulated launch and re-entry, while a control group experienced isolation and confinement without the jolts, allowing the researchers to compare the different conditions. The researchers recreated key aspects of the Cosmos 1129 mission, including group housing, mating opportunity, diet, simulated launch and re-entry stresses, and post-recovery isolation.

However, the results complicated the idea that launch and re-entry stresses alone caused the reproductive problems. The majority of females, including those exposed to the effects of simulated launches and re-entries, gained weight in a way typical of pregnancy, while females in the experimental groups went on to deliver healthy litters. These results indicated that the mechanical stresses involved in the simulated flight were not, by themselves, enough to prevent pregnancy and delivery. At the same time, the researchers found that parturition was delayed in the stressed groups compared with the controls. The difference in the timing of birth was statistically significant, while the researchers also observed other changes in reproductive outcomes, including differences in litter size and embryo resorption. The findings therefore did not point to a single factor as the cause. As Sabelman and his colleagues noted, several conditions associated with the simulated mission, including confinement, diet, stress, and the spacecraft environment, could have contributed to the reproductive effects.

It is also worth noting that the timing of pregnancy mattered when interpreting the experiment. Because the rats were allowed to mate only after the partition was removed, there was not enough time for a normal rat pregnancy to be completed during the 18.5-day mission. The experiment was therefore concerned with whether mating and the beginning of pregnancy could occur in orbit, with the animals able to continue the pregnancy after returning to Earth.

The lesson that has nothing to do with rockets

Crowded conditions, lack of normal lighting, competition for available resources, and disruption of the schedule were among the factors considered by the researchers when examining the reproductive results. Rather than identifying one of these conditions as responsible, the study looked at how several features of the simulated mission could work together. The researchers also used adrenal-gland weight relative to body weight as an indicator of chronic stress, and found that rats fed special flight food accumulated significantly more abdominal fat than rats fed standard food. Diet by itself therefore had a noticeable effect on the animals' body composition.

The experiment showed how several conditions associated with a simulated spaceflight could affect reproductive outcomes. The researchers did not identify a single factor as responsible. Instead, their findings pointed to a combination of diet, stress, the spacecraft environment, and weightlessness as possible influences on mating and the viability of pregnancies. In the actual Cosmos 1129 flight, the rats did not produce successful pregnancies, while the ground-based simulations showed that reproductive activity could still occur under comparable conditions, although parturition was delayed. The study therefore suggested that the reproductive effects observed during the mission could not be attributed to launch and re-entry stresses alone.