LONG ISLAND, New York USA — To make their rockets launch, Walter Roller kindly explained Saturday to the crowd of transfixed Cub Scouts, they had to drop the solid fuel into the liquid fuel and screw the top on tight.

To screams of delight, a half-dozen film canisters disguised as rockets flew about 15 feet into the air, powered by the potent combination of hot water and Alka-Seltzer, and landed harmlessly on the concrete sidewalk outside the Cradle of Aviation Museum.

VIDEO: LIARS at Rocket Fest.

"It was cool," said Katelynn Brown, 12, of Farmingdale, the lone girl in the circle of Scouts. "I was scared a little."

To produce the mini-rocket launches, Roller, a Cradle of Aviation educator from Garden City, collects used 35-millimeter film canisters from Nassau pharmacies. When he has the rapt attention of a circle of kids, he fills the canisters halfway with hot water and hands each child a piece of an Alka-Seltzer tablet.

"Now drop the solid rocket fuel into the liquid fuel," Roller said. "Put the rocket on the ground and run!"

The kids' rocket launch came in between the high-power rocketry exhibitions in the Cradle's parking lot. There, to oohs and aahs from the assembled crowd, the Long Island Advanced Rocketry Society shot up a series of large rockets once an hour.

The rocket launches were part of Long Island Rocket Fest, a free event organizers hoped would bring together rocketry enthusiasts and attract a few people headed inside the museum to watch the latest Harry Potter movie on the Cradle's IMAX screen. Rocket Fest ends Sunday, after a noon start.

Robert Meyers, an attorney and doctoral student from Hollis Hills, Queens, sat watching the large rockets with three of his mop-haired sons: Daniel, 8, and twins Jeremy and Jonathan, 4.

One of the demonstration rockets fired a shuttlecock some 75 feet in the air, high above the parked cars. While his brothers cheered softly, Jonathan kept his left thumb firmly planted in his mouth.

"I think we're getting close to nap time," Meyers said.

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