The barrel of the full-scale version would be 3km (1.9 miles) long and have a calibre or diametre of 1.7m (1.9 yards). It might be permanently dug-in inside a mountain to launch satellites at a fraction of today's rocket costs.
Researchers on the supergun project at a leading US weapons laboratory said the success of their first tests with the prototype gun - which fired projectiles horizontally into a nearby hillside - vindicates going ahead with the second and third phases of the project.
The Lawrence Livermore National Laboratory in California said it had shown the feasibility of using gas guns, which use exploding hydrogen rather than gunpowder, to fire objects at up to 25,000mph - fast enough for a satellite to enter an orbit around the Earth.
It is not certain, however, whether the laboratory, already suffering from cutbacks in weapons development, will ever have the funds to develop the technology.
The laboratory estimates it will cost about dollars 6.6bn ( pounds 4.5bn) to build a working supergun, which it suggests should be called the Jules Verne Launcher after the French science fiction writer who, in his 1865 novel From the Earth to the Moon, proposed sending a spaceship from Florida to the Moon using a giant cannon.
'Although we are in the early stages of this project, we are attempting to do in reality what Jules Verne imagined,' John Hunter, a scientist at the Livermore Laboratory, said
Livermore's Super High Altitude Research Project (Sharp) is also reminiscent of Saddam Hussein's plan for a supergun to fire missiles from Iraq to Israel. In fact both ideas have their roots in a 1960s research project called Harp funded by Canada and the US and led by Gerald Bull, the Canadian weapons scientist who helped Iraq to develop supergun technology before he was assassinated in 1990.
Shells fired from the superguns developed under the Harp project did not reach the enormous speeds necessary to enter the Earth's orbit, but they were estimated to have travelled more than 1,000 miles with the help of small rocket boosters.
Livermore scientists believe the advantage of the Jules Verne Launcher over conventional rocket launchers is cheapness. It currently costs about dollars 10,000 ( pounds 6,900) to launch a kilogram of material on an unmanned rocket; the cost of launching by supergun might be 5 per cent of that.
The prototype gun tested by the Livermore Laboratory is a unique design with the barrel of the gun running at right angles to a high-pressure steel tube where the explosive gases are ignited.
However, the recent invention of devices called particle beds for heating hydrogen very quickly, has led the laboratory to explore a new approach. The devices could be distributed along the gun barrel to eradicate the enormous shock of a single explosion.
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