Light-gas gun

Some basic material research relies on projectile impact to create high pressure; such systems are capable of forcing liquid hydrogen into a metallic state.

A large-diameter piston is used to force a gaseous working fluid through a smaller-diameter barrel containing the projectile to be accelerated.

In a light-gas gun, the piston is powered by a chemical reaction (usually gunpowder), and the working fluid is a lighter gas, such as helium or hydrogen (though helium is much safer to work with, hydrogen offers the best performance [as explained below] and causes less launch-tube erosion).

In this conical section is a stainless steel disk, approximately 2 mm thick, with an "x" pattern scored into the surface in the middle.

These guns have been used in support of various missions beginning with Apollo program reentry studies in the 1960s and most recently for high-speed thermal imaging.

The largest of these involves a 6.25-inch (159 mm) diameter piston weighing more than 46 pounds (21 kg) to compress the hydrogen.

Arnold Air Force Base's Range-G is the "largest routinely operated two-stage, light-gas gun system in the United States".

[4] The primary use of the range facilities at Arnold Air Force Base is the measurement of released kinetic energy upon projectile impact.

Spring piston airguns increase the temperature of the air in the chamber by adiabatic heating; this raises the local speed of sound enough to overcome frictional and other efficiency losses and propel the projectile at more than the speed of sound in the ambient conditions.

With materials in a wide range of densities (from tungsten powder to glass microspheres) applied in thin layers, carefully made projectiles can be used in constant-pressure experiments, or even controlled compression–expansion–compression sequences.