University of Arizona Airgun Facility

This facility can accelerate instrumented projectiles up to 8cm in diameter into targets. It is presently being used in support of the DS2 microprobe mission to relate impact accelerometer data to soil properties and determine how thin layers can be resolved. The impact velocity depends on the pressure to which the gun is pumped, and the mass of the projectile. Presently tests are ongoing in the 50 m/s range.

Airgun - green tank at right is pumped with air. Solenoid valve allows air to blow projectile (held at top of tube) down into target

Detail of top of gun. Circular aluminum plate allows feedthrough of accelerometer cable. Solenoid at left lifts bar allowing valve to blow open

Detail of bottom of gun. Target material is assembled in bin at bottom. Slots in barrel minimize blowout of material. Just below those is a black plastic section containing two pencil leads across the projectile path: a resistor network partially shorted by these leads generates a square voltage pulse which indicates the speed of the projectile. Aluminium box at right contains charge amplifier to boost accelerometer signal.

Penetrator assembly. The penetrator is the same dimensions and approximate mass as the DS-2 forebody. It is held in an aluminium sabot for acceleration in the airgun. Swiss army knife for scale. Black groove is for shear pin to hold sabot at the top of gun before firing. A similar technique holds the penetrator in the sabot

The various components

An Endevco 2225 piezoelectric accelerometer is mounted in the back of the penetrator. A small aluminium cone prevents strain on the connector.

A kevlar-reinforced miniature coaxial cable is coiled in the sabot, and unwinds in the gun barrel as the sabot accelerates downwards

Result - projectile is buried in target (in this case a layer of sheetrock above sand)