In February, the Spanish pilot Daniel González climbed into a small aerobatic plane at the Sabadell Airport outside Barcelona and fired up its single prop engine. Once he was in the air, González began a steep climb for about six seconds before entering a nosedive. The plane’s rapid descent created a microgravity environment in the cockpit and for a few seconds, González felt what it was like to be an astronaut. Then he pulled on the yoke to bring the plane out of its dive and did it all over again.

This sort of parabolic flight isn’t remarkable for an experienced aerobatic pilot like González. But the cargo on his flight was a little unusual: In the passenger seat of the plane sat a small box, loaded with tubes of frozen human sperm.

This was the third and final flight of a yearlong study undertaken by a group of Spanish researchers to understand the effects of microgravity on human reproduction. This seminal study, which is currently under peer review, marks the first experimental results published on the effects of a zero-gravity environment on frozen sperm. The study was limited—the sperm was in microgravity for less than 9 seconds, for example—but it suggested that reduced gravity has negligible effects on the health of frozen sperm.

“We are at the frontier of knowledge about human reproduction in space,” says Antoni Perez-Poch, an engineer at Polytechnic University of Catalonia and a coauthor on the paper.

Perez-Poch and his colleagues are not the first to experiment on sperm in zero G. Last year NASA dispatched frozen human sperm to the ISS, though the agency has not shared any results. These projects are all part of a nascent push to see how human settlements, and extraterrestrial babies in particular, might fare beyond Earth.

Perez-Poch says the team plans to conduct more, longer flights, and hopes to also do experiments with thawed sperm. Because the samples have to be kept warm to survive, working with frozen material was an easier way to begin. NASA also plans to thaw its sperm on the ISS before sending it back to Earth. Microgravity is only one concern for the creation of outer space babies; then there’s the high radiation to consider too. The effects on ova, and eventually embryos, will also need to be scrutinized.

With all the ethical challenges of working with human embryos, the long-term research agenda for conception in the cosmos is fraught, at best. The idea of human reproduction in space, however, has taken on a life of its own. At least one company has already set out to offer couples the option of doing IVF in low Earth orbit—as if in vitro fertilization wasn’t expensive enough.

Last year, a company called SpaceLife announced its intentions to store frozen sperm and eggs in satellites and to develop an in-space embryo incubator. In July, though, the company halted operations, citing “serious ethical, safety, and medical concerns.”

Given how little we know about how the space environment affects human reproduction, this is probably for the best. But maybe one day we will find ourselves in a world where babies are delivered not by stork, but by spacecraft.

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