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
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)