LIVERMORE, Calif. -- In the dusty hills east of Livermore, physicist John Hunter is working toward a $3 billion supergun two miles long that will hurl payloads to the moon.
His first scaled-down, $4 million test version of the gun is nearly done. Its barrel, half a football field long, is the longest of any known gun in the world. Its first firing in September will be somewhat more modest than a space launch, flinging an 11-pound piece of plastic at 9,000 mph into a pile of sandbags.
But to Mr. Hunter, it's a big step. "This is a great gun," Mr. Hunter, a Lawrence Livermore National Laboratory physicist, said admiringly one recent afternoon while standing next to his creation.
The size of Mr. Hunter's cannon puts it in a league with the superguns that Iraqi President Saddam Hussein's scientists built to bombard Israel, the ones that United Nations inspection teams found and destroyed after the war.
But Mr. Hunter is not building his gun as a weapon. He readily acknowledges that that could be done, but says that as a weapon it would be wildly expensive, make an easy target and wouldn't be nearly as flexible as the airplanes and missiles the United States already has in abundance.
Mr. Hunter is interested in space exploration and wants to use the gun to launch food, fuel and building materials into orbit around the Earth or to the moon, in conjunction with NASA's step-by-step voyage to Mars.
While nobody knows if the gun will work, the idea was intriguing enough to get Mr. Hunter grant money from a lab fund for innovative research. He also received funding from the Strategic Defense Initiative, or "star wars," program.
He figures that, with the American space effort desperate for cheaper launches, and the temperamental shuttle fleet tying up NASA's resources, the time is right for a dependable device that will fire goods into space for less money, day after day.
It would not, however, be a ride for sensitive cargo. A version of the gun large enough to throw a payload to the moon would slam its cargo with a launch force 1,400 times more powerful than gravity.
Mr. Hunter said his gun could not be used to launch Macintosh computers or fragile scientific experiments. But construction materials, food and water would survive in good shape. The water could be "cracked" in orbit or at a moon station into its two ingredients, hydrogen and oxygen, which would then be used to fuel a Mars spaceship.
But that's in the future. Today Mr. Hunter has several hundred feet of very expensive steel pipe fastened to the ground in the shape of a giant L. The small part of the L is the gun barrel, and it is pointed not at the sky but horizontally, straight at the side of a hill a mere 100 feet away.
Mr. Hussein's superguns -- U.N. inspection teams found evidence of five of them -- were giant versions of classic gunpowder-driven artillery pieces. Mr. Hunter's gun, on the other hand, is an oversize version of a research device known as a gas gun. It uses an explosion in one end of a pipe to compress gas to a very high pressure at the other end, and then uses the gas to spit out a projectile.
"It's very low-tech," Mr. Hunter said. "It's a big tube of compressed gas. It's like a BB gun.
"This is the world's biggest gas gun," he said. "I wanted to make sure it would punch through the atmosphere."
Launching satellites with gas guns "is an intriguing idea, and some people become very bewitched by it," said Alex Charters, a gas gun expert at General Research in Santa Barbara, Calif., who served as Mr. Hunter's adviser.
"There's no question that you could do it theoretically," he said, but he had recommended that Mr. Hunter try out a smaller version before building the Livermore gun.
"There's an old rule that big mistakes are only made on big guns," Mr. Charters said.