Gun to launch objects into orbit

In Jules Verne's 1865 story From the Earth to the Moon, a gun club constructs a massive cannon to launch a spaceship to the moon. Since then, the technical feasibility of a space cannon has been raised, not for human missions but rather to launch supplies. Project HARP, started in 1961 by the US and Canada, was one example. The New Scientist Space Blog reports on the latest exploratory research in this area, by physicists at the University of Ferrara in Italy. In an Acta Astronautica journal publication, they present their theory of a "multistage light gas gun," describing the "application of such a gun to satellite or robot craft launching." From New Scientist:

...Much higher efficiency can be achieved with a multi-stage gun, where the energy of an explosion is channeled through a series of tubes and pistons that accelerate the projectile, rather than accelerating it directly.

Although such a gun would be more efficient, the authors admit that there are other hurdles, such as the intense heating the projectile would experience during its high speed passage through the atmosphere. "We have not treated the many technological difficulties inherent in the realization of such a gun," they say.

Link to New Scientist, Link to Acta Astronautica abstract

Update: BB reader Steve Glista writes:

I thought other readers might like to see that there's a good write-up of the physics involved in shockwave acceleration and light gas guns on Wikipedia (link) and that there are several of these things already built and working, although on a scale that is much too small to send large masses into space.