According to the United Network for Organ Sharing, about 113,000 people in America are waiting for donated organs to save their lives. While organ donation is on the rise, these waiting patients desperately need other options. NASA is trying to help.

Astronauts at the International Space Station began trials this year of a 3D bioprinter that may one day be able to print viable human organs. The “ink” being used contains human stem cells. Ideally, printed bioforms eventually will be made complex enough to function as human organs. Then, they’d be transplanted into patients urgently needing lifelines.

A tech company based in Indiana invented the printer, but the developers can’t test it to its full potential because of gravity. Printed 3D bioforms are soft and delicate, and earthly gravity makes them sag. In space, it’s a different story. Soft printed forms can hold their shapes.

That’s why the latest tests are being done at the space station. The tests have begun with the astronauts first attempting to make heart tissue. After printing, specialized containers will be used to transport the tissue back to earth. The scientists who invented the printer will examine the tissue to see how it turned out, and later test it in animals. The company hopes to start printing organs by year 2025.

If 3D organ printing works, it could overcome an enormous obstacle of transplantation: organ rejection. The ultimate goal is to print organs using healthy cells from the patient’s own body. For patients desperate for an organ, this truly would be a lifesaving breakthrough.

It sounds like science fiction, but it’s happening right now, right above our heads.