In 1989, the space shuttle Discovery carried 32 fertilized chicken eggs for 5 days; all 16 early embryos died, while 8 older embryos later hatched without anatomical malformations

In March 1989, the space shuttle Discovery took an unusual group of passengers into orbit: 32 fertilized chicken eggs. A 1996 study titled ‘Microgravity in the STS-29 space shuttle Discovery affected the vestibular system of chick embryos’ conducted at Tulane University School of Medicine and published in the journal Histology and Histopathology divided eggs into two groups according to age. Sixteen were just two days into development, and sixteen were nine days old. All spent five days in weightlessness before Discovery landed. The results varied dramatically depending on how far each embryo had developed when the flight began.

The unlikely sponsor behind the experiment

The eggs were not unique to NASA. A science fair project sparked by a ninth-grader from Lafayette, Indiana, John Vellinger, asked how gravity would affect a developing chick embryo, an idea he carried through high school under the name "Chix in Space." As Space.com's spaceflight historian Robert Z. Pearlman writes, by the time he reached Purdue University as a freshman, NASA had found him a corporate sponsor: Kentucky Fried Chicken, which sponsored the flight incubator and lent its own engineer, Mark Deuser, to help build it. A previous version of the experiment flew on board the shuttle Challenger in January 1986 but was lost when Challenger broke up 73 seconds after liftoff. Three years later, STS-29 carried a rebuilt version of the same incubator, stowed in a locker on Discovery's pressurized middeck, while the mission's main payload, a NASA communications satellite, rode separately in the cargo bay. NASA's mission logs show that Discovery launched from Kennedy Space Center on March 13, 1989, and touched down five days later at Edwards Air Force Base in California.


Why the younger embryos didn't survive

The younger group, who were only two days old at the start of the flight, did poorly. When Discovery landed, all 16 of the early-stage embryos were dead, the study reports. Eight of the embryos were studied in person by the scientists, and, as a simultaneous ground-based comparison, another eight eggs from the same younger batch had been incubated at Earth's gravity the whole time instead of flying. In the end, all sixteen were confirmed dead, though autopsies revealed four of them had lived more than 24 hours in space before they died. The study does not identify a single clear cause of death. It simply notes that this very early stage of development seems to have posed difficulties for survival in the conditions of spaceflight.

The older embryos told a different story

The second group, nine days old at launch, did much better. After five days in orbit, these embryos had developed to the equivalent of day 14. The paper says eight of them hatched normally and showed no apparent physical deformities. The first chick to hatch, less than a week after landing, was named “Kentucky” and was sent to live at the Louisville Zoo. The other eight embryos were not hatched, allowing the scientists to examine their tissues under a microscope, especially the inner ear.

What the inner ear revealed

The inner ear contains the vestibular system, a set of tiny organs that helps animals, including humans, sense balance and motion. This is where the study’s most granular results came to light. The researchers found that in the hatched flight chicks, the sensory tissue layer inside the balance organs was thinner than in chicks raised entirely on the ground. The tissue, known as the macular epithelium, measured about 26 micrometers in the flight chicks compared with 31 micrometers in the controls. A micrometer is a millionth of a meter, about one-twentieth of the width of a human hair, so these were small but measurable differences.

The study also found more nerve fibers in this balance-sensing tissue in the flight chicks. In 3 of the 8 flight chicks, a stronger signal was needed to evoke a balance response, but otherwise, the speed and strength of the response were normal. The researchers suggested this could be due to changes in the patterns of nerve connections formed during the flight, which could take weeks to correct themselves after landing. There was no significant difference between the two groups in the cartilage and other ear structures.

Why this old experiment still matters

The three-decades-old study seems newly relevant as NASA prepares for longer journeys to the Moon and beyond. Unlike the brief Apollo flights, Artemis missions will last for weeks in space, giving astronauts’ bodies more time to adapt to weightlessness, and more time to struggle when they readjust to gravity afterward. Astronauts coming back to Earth often experience motion sickness and trouble doing things such as walking or getting up after a fall, largely because their vestibular system has adapted to working without gravity, a study titled ‘Potential benefits and human systems integration of parastronauts with bilateral vestibulopathy for a space mission’ published in Frontiers in Neurology in 2025 explained. The paper also suggests that astronauts who already have vestibular disorders and can get through their daily activities without relying on the balance cues of the inner ear may be better able to cope with these transitions than astronauts with normal vestibular function.

The science fair project from a ninth-grader sponsored by a fried chicken chain generated real data about how the inner ear develops under stress. Whether it's a chick embryo nine days old on a space shuttle or an astronaut emerging from a lunar lander decades later, that adjustment process runs on the same biology.