Light Gas Gun

Published on 19 May 2022. Written by Bheru Singh

About the project

The light-gas gun is an apparatus for physics experiments, a highly specialized gun designed to generate very high velocities. Basically adopted to study and understand the high-speed impact phenomena, leading to the formation of impact craters by meteorites or the erosion of materials by micrometeoroids. Some basic materials research relies on projectile impact to create high pressure: such systems are capable of forcing liquid hydrogen into a metallic state.

A light-gas gun works on the principle similar to the spring-piston air gun. A piston with large diameter forces a gaseous working fluid through a smaller-diameter barrel which contains the projectile which has to be accelerated. The reduction in diameter increases the speed while decreasing the pressure.

In a light-gas gun, the large piston is powered using chemical energy produced by gunpowder and the working fluid is a lighter gas, such as helium or hydrogen. The maximum amount of energy is available when the projectile begins moving and this is done by rupture disk which creates the high pressure to the desired level behind the disk, the disk tears open, allowing the high-pressure, light gas to pass into the barrel.

One particular light-gas gun used by NASA uses a modified 40–mm cannon for power. NASA also operates light-gas guns with launch tube sizes ranging between 4.3 mm to 38 mm carried out at Ames Research Center and 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 limiting factor on the speed of an air gun, firearm, or light-gas gun is the speed of sound in the working fluid—the air, burning gunpowder, or a light gas. This is essential because the projectile is accelerated by the pressure difference between its ends, and such a pressure wave cannot propagate any faster than the speed of sound in the medium. The speed of sound in helium is about three times that in the air, and in hydrogen 3.8 times that in the air.

The speed of sound also increases with the temperature of the fluid being independent of the pressure so the heat formed by the compression of the working fluid serves to increase the maximum possible speed. 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.

The hybrid electro thermal light-gas gun works on similar principles of the standard light-gas gun but adds an electric arc to heat the light gas to a higher temperature and pressure than the piston alone.

When the projectile fired by a light-gas gun impacts its target, the pressure applied depends upon the mass of the projectile and the surface area, or cross-section, over which the impact force is distributed because air-launched projectiles experience friction with air molecules, drag increases proportionally to increased projectile surface area, which results in slower velocities the larger the surface area of a projectile is.

Kit required to develop Light Gas Gun:

Technologies you will learn by working on Light Gas Gun:

Light Gas Gun

About the project

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