WALTERBORO, S.C. (WCIV) -- Four Walterboro middle school girls wanted to find a way to keep astronauts healthy while in space -- and their experiment made it all the way to the International Space Station.

Through a science competition called the Students Space Flight Experiments Program they were able to test how long it takes for milk to spoil in space compared to Earth.

We tested whole milk, skim milk and one percent milk ultra-pasteurized, said Amber Avant, a seventh grader in the group. We did it because those types of milks are most common. We tested the two milks for a month.

The students got the milk back from space on Thursday. Over the past 24 hours they've been studying the difference between the two.

We found out that the milk in space lasts longer, said Avant. So far our theory is because there is less bacteria in space and it's more sanitary, and one of the necessities for milk to spoil is bacteria.

The girls started the project because they say astronauts have to drink powdered milk while in orbit.

They hope their experiment changes that.

"Astronauts in space have less bone density and the proteins in milk help strengthen your bones, said Megan Dewitt, another seventh grader in the group. So since they have less bone density, the milk will help them get stronger bones. That's why we sent it, because they have to have powdered milk up there which has no proteins in it and doesn't help them as much as the milk would."

As the group of Colleton County Middle School students continue their project, they hope to go to Washington, D.C. this summer to present their work.

To help the girls get to D.C., click here.

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Milk experiments sent to space returns to Walterboro students