Environmentalists are counting on hydrogen to replace greenhouse gas producing gasoline in cars and trucks, because it’s colorless, odorless and its byproduct is water vapor. But hydrogen has such a small molecule that it can easily escape, making it hard to keep it inside your gas tank. Liquid hydrogen doesn’t escape as easily, but it needs to be kept cold, meaning your car would also have to be a refrigerator. NASA has come up with a solution: put rocks in your gas tank.

NASA’s Al Sacco says these aren’t ordinary rocks?they’re zeolites. He says, “Zeolites are porous, rocky substances that act like molecular sponges.” Your car’s fuel tank would be lined with 93 pounds of zeolites. You would pull into a hydrogen fueling station and ask the attendant to force 7 pounds of hydrogen into your the tank (or you’d do it yourself). “If we can grow zeolite crystals that hold 7% of their own weight in hydrogen,” says Sacco, “then a zeolite tankful of hydrogen would be competitive with an ordinary tankful of gasoline.” However, the zeolites we have right now can hold only 2% to 3%. The only way to solve this problem may be to grow zeolites in space.

In 1995, Sacco traveled onboard the space shuttle Columbia to see if he could grow better zeolite crystals. “In low-gravity, materials come together more slowly, allowing zeolite crystals to form that are both larger and more orderly,” he says. They were also grown in the International Space Station. He says, “Now we need to get those crystals back to Earth where we can examine them. A few might come down in May. I’d really like to see them.”

Hydrogen-fueled cars have been a mainstay of science fiction for years?now they may become a reality. Did you know there’s a reality behind the Lord of the Rings? Find out the real legends that inspired Tolkien.

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