The first leg of the experiment's trip home was via space capsule, plunging 250 miles from the International Space Station to the Pacific Ocean.
FedEx carried the tiny package the rest of the way to Hillsborough County.
Three scientists — all sixth-graders from east Hillsborough — unpacked the 6-inch plastic tube that housed their experiment on May 19, eight days after it returned to Earth.
"I'm touching space right now," Casey Utsler, 11, said while she and her teammates — Chandrika Gandrui, 12, and Karinna Crespo, 12 — analyzed the results at Bloomingdale Regional Public Library.
The goal of their experiment was to determine if cottonseeds could germinate, or grow, in a low-gravity environment. The girls hope their experiment could one day help space explorers produce their own food, clothing and medicine for a manned mission to Mars.
Their space experiment was also part of a grander one: SpaceX founder and chief executive Elon Musk's dreams of revolutionizing space travel with reusable rockets.
The cottonseeds were launched into space April 8 aboard a SpaceX Falcon 9 rocket, which then made the first successful landing on a barge at sea. Musk hopes his SpaceX venture can drastically reduce the cost of space travel by reusing rockets.
The students watched the launch at Kennedy Space Center. They hope their more modest experiment can advance space travel, too.
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The experiment's return to Earth last month marked the end of an 18-month wait for the girls. An identical experiment was aboard a SpaceX rocket that exploded on June 28, 2015, less than three minutes after launch. The girls attended Fishhawk Creek Elementary in Lithia then. They re-created the experiment after moving on to middle school.
The experiment is made of three identical tubes. Clamps divide each tube into three compartments. Each of the two outside compartments held three seeds wrapped in felt, for a total of six seeds per tube. The middle compartment contained water. One tube went into space. Two stayed on Earth as a control group.
Two days after one of the tubes arrived at the space station, an astronaut removed one of the clamps and shook the tube to expose seeds on one side to water. Then, 14 days before the experiment was to return to Earth, an astronaut removed the other clamp and shook the tube, exposing the seeds of the other compartment to water.
The students performed the same procedures on the two tubes left on Earth.
The results were promising. Four of the six space seeds germinated in zero gravity. Those seeds did better than the ones left on Earth; only four of 12 germinated in Earth's gravity.
"I thought Earth would have more germination because it's what the seeds usually go through," Casey said. "But then in space (the seeds) did better."
There was a variable they can't account for, however: how vigorously the astronauts shook the tubes.
"Maybe when we shook the Earth tubes, we didn't shake them the same amount as the astronauts did up in space," Chandrika said.
"That could have changed the amount of water the seeds got," Karinna said.
They also considered other factors. Some of the Earth samples developed mold in the felt, which could have hindered growth. And the students worried that packing too many seeds into such a small space may not have given them enough room to sprout.
Still, the project could have a "huge impact," Chandrika said.
"The whole reason we started this project was to see if cotton can be useful in space," she said, "and now we have proof that it can be grown in space."
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The cottonseed experiment competed against 49 other proposals submitted by Hillsborough students to district officials, who picked three finalists. Then Student Spaceflight Experiments Program, which arranges for student experiments to go into space, picked the winner.
In all, the experiment cost about $21,500, the vast majority of that paying for the ride into space. A Suncoast Credit Union grant covered much of the cost.
Mary Vaughn, a science academic coach with the Hillsborough County School District and local project manager for SSEP, handled the logistics.
But the science was left to the students.
"The team did all the work," she said. "I only guided them. But the whole project itself was their idea."
The next step for the kids is to do what adult scientists do: present their findings. The Hillsborough trio will travel to Washington, D.C., for a June 29 conference to share their results and the implications of their findings with other students.
After that, Chandrika said, the sky's the limit.
"I want to become an engineer at NASA so maybe I can design a rocket or a rover," she said. "Because I want to expand the way I think about space."
Contact Josh Solomon at (813) 909-4613 or [email protected] Follow @josh_solomon15.