Impact Research: Light-Gas Guns
On earth projectiles are accelerated to hypervelocity using two-stage light-gas guns.
A diagram of a typical light-gas gun is shown below. The first stage is a larger diameter
cylinder filled with compressed (50 psi) hydrogen gas. The breech contains a powder charge,
while the other end of the cylinder, called the pump tube, is tapered. Inside the pump tube
is a nylon piston; when the powder charge is ignited, the piston is propelled down the pump
tube to the end of the first stage, compressing the hydrogen gas to extremely high pressures.
1. Breech block 2. Chamber 3. Propellant charge (gun powder)
4. Piston 5. Pump tube 6. Light gas (helium or hydrogen)
7. Rupture disk 8. High pressure coupling 9. Projectile
10. Gun barrel
Credit: Johan Fredriksson [CC BY-SA 3.0]
via Wikimedia Commons
The second stage of the light-gas gun consists of the barrel, the flight range, and the target
chamber, and is separated from the first stage by a scored rupture disc. The projectile is located
at the front of the barrel, just downrange of the rupture disc. The pressure in the second stage,
like space, is near vacuum.
When the pressure in the first stage becomes sufficiently high, the rupture disc fails, releasing
the hydrogen gas at hundreds of thousands of pounds of pressure into the vacuum of the second stage.
The rapidly expanding hydrogen propels the projectile down the barrel to the target. With the high
pressure behind, and the vacuum in front, the projectile will reach velocities in the neighborhood
of 7 km/s before striking the target.