GENERAL INFORMATION

BALLISTIC RANGES

Ballistic ranges are needed for nearly all studies and tests using guns. They  extend in size from tabletop units used for simulating small meteoroid impacts on spacecraft components to large outdoor facilities, multiple kilometers long,  used for observing artillery projectiles in flight. Common among them are:

  • guns for launching projectile packages
  • mounts to support/aim the guns and provide needed services for them
  • space for projectile flight
  • provisions (target holders) for intercepting launched projectiles
  • instrumentation for measuring projectile launch velocity and observing other characteristics of the experiment/test.

Physics Applications Inc. supplies complete ballistic range systems, many range components, expertise in design, installation and testing of range setups, and consultation on experiment/test design.

 

RESEARCH LAUNCHERS

Launchers for ballistic research/testing fall into three categories, each of which has many variations. The three categories are listed below along with their launch velocity capabilities.

  • Powder Guns, 0.3 km/sec - 2.7 km/sec
  • Single Stage Gas Guns, 10 m/sec - 1.5 km/sec
  • Two Stage Light Gas Guns, 1.5 km/sec - 10 km/sec.

Uses for research launchers


1. POWDER GUNS

The most common ballistic launchers for range work are single stage solid  propellant guns "powder guns". With these, solid propellant is burned in a  chamber to produce high pressure gas that accelerates a projectile package along  a launch tube. The tube may be rifled or smooth-bore depending on whether  projectile rotation is needed.  PAI has produced powder guns with bore diameters between  4.3 mm (0.17") and 200 mm, 8.0".  Powder guns operate effectively at launch  velocities between 0.3 km/sec (985 ft/sec) and 2.7 km/sec (8800 ft/sec). Specially designed low performance guns can extend the low velocity limit to below 0.1  km/sec (325 ft/sec).  Peak projectile acceleration levels and gun wear become significant concerns when velocities over 2.0 km/sec (6,600 ft/sec) are routinely sought.

More about powder guns

 

2. SINGLE STAGE GAS GUNS

Single stage gas guns use chambers filled with various gases to relatively high pressures to power their operation. At firing, a fast valve opens to expose the gas in the chamber to the rear face of a projectile package located at the rear end of a launch tube.  Expansion of the gas accelerates the package within the launch tube. Such guns can launch packages effectively to very low muzzle velocities, down to about 10 m/sec (33 ft/sec).  When air is used as driver gas, peak velocities up to 0.4 km/sec, 1300 ft/sec can be achieved. Helium gas at very high pressure can launch relatively light packages along  lengthy launch tubes at velocities up to 1.6 km/sec (5,250 ft/sec).

Obviously, velocity capability of single stage gas guns widely overlap those of powder gun so choices in launch technology must be made between them.

Single stage gas guns have the following advantages and disadvantages when compared to powder guns.

ADVANTAGES

  • Many laboratories find the storage and use of compressed gas more acceptable from  safety considerations than solid propellant.
  • Gas gun operation is clean compared to that of solid propellant guns which emit burned propellant residue.
  • Gas guns are clearly the best choice for work requiring low projectile package velocities.
  • Peak launch accelerations for achieving similar muzzle velocities are  generally less than those needed by powder guns.
  • Gas guns with bore diameters up to 300 mm (12 inch) and beyond can be constructed for reasonable cost.

DISADVANTAGES

  • The performance capability (projectile mass vs. velocity) for a given bore diameter is much lower.
  • Relatively large gas loads are used compared to powder guns launching  similar packages, (which increase muzzle blast).
  • Often requires gas pressures in excess of 400 bars (5,800 psi) to obtain velocity greater than 1,200 m/s (4,000 ft/s).

More about single stage gas guns

 

3. TWO STAGE LIGHT GAS GUNS

Two stage light gas guns use a smooth-bore powder gun to launch a freely moving piston along a tube (Pump Tube). The piston compresses a charge of low molecular  weight gas (typically hydrogen or helium) initially loaded into the pump tube to under pressure. A fast valve (e.g. burst diaphragm) at the forward end of the launch tube then opens to expose the built up gas pressure to the rear of a projectile package mounted in the launch tube.  The oncoming piston continues to increase  pressure of the light gas column well after the valve opens and the projectile is released so that very high acceleration levels can be applied to the projectile smoothly.

Two stage light gas guns are effective for launching projectiles to velocities between 1.5 km/sec (4900 ft/sec) and 10.0 km/sec (33,000 ft/sec).  As "stunts", they have  been operated at velocities just above 12 km/sec (39,400 ft/sec). Two stage light gas guns represent effectively the only technology available for reaching the velocity  regime above 2.75 km/sec (9,000 ft/sec) with projectiles of precisely controlled sizes, shapes and masses. Two stage gas guns are also useful in the overlap velocity range with powder guns (1.5 km/sec to 2.5 km/sec) when minimum peak launch acceleration levels are needed for launching delicate packages.

More about two stage light gas guns

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GUN MOUNTS

Gun mounts take on a variety of forms, which depend largely upon configurations of the guns that use them.

Many research guns have relatively long launch tubes that often consist of multiple connected sections requiring adjustable mounts for tube alignment. Some gun configurations, such as two stage gas guns consist of multiple coupled components spread along a  substantial length that must be separated after each firing for gun cleaning and preparation for firing.

Mounts of choice for such guns consist of one or more structural beam weldments that support the gun components above their top surfaces and in alignment  with one another via several individual mounts. Recoil from such guns is absorbed by shock absorbers connected between gun components and the base beam.

The gun mount also contains equipment that supports gun operation such as:

  • gun component positioners that are used to move large heavy components
  • hones that are used to clean/smooth launch tube bore surfaces
  • hydraulic systems that are used to for gun operation and maintenance
  • equipment for evacuating air from gas gun pump tube and inserting charges of light gas
  • electrical/pneumatic control systems for controlling other range operations.
  • gun firing system components.

More about gun mounts

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PROJECTILE FREE FLIGHT AREAS

All ranges require some distance for projectiles to fly from the gun muzzle to their targets.

ENCLOSED RANGES

While some ranges are open to ambient atmosphere, either indoors or outdoors, most ballistic research guns are fired into enclosures of tanks and tubes within which products of the firings (i.e., muzzle blast, projectiles, discarded sabots, impact debris, etc.) can be contained. Enclosing the range trajectory allows instrumentation and other equipment to be positioned near the trajectory without risk of damage.  Enclosed ranges can be made safe to operate in conventional laboratories where adjacent  personnel presence cannot be controlled.

CONTROLLED ATMOSPHERE RANGES

Ranges whose atmospheric conditions can be controlled are used widely for a  variety of purposes. The range trajectory is contained within sealed tanks and  tubes so that most of the ambient atmosphere can be removed through mechanical evacuation.  Evacuation greatly reduces air resistance to projectile movement.  Reduced air resistance minimizes projectile free flight velocity loss and eliminates intense heating and ablation to hypersonic projectiles. An extreme evacuation requirement is imposed for ranges where planar  shockwaves are produced in targets by impacting them with flat plates. Free flights of less than one launch tube bore diameter are chosen so that  parallelism between the flat projectile and target face can be maintained within angles of 1.0 milliradian (0.06) or less.  Gas originally in the gun's launch tube is compressed by the oncoming projectile to form a cushion between the two surfaces just before impact. Experience has shown that ballistic ranges used for these types of shock physics experiments must be evacuated to 50 mtorr (50mm) Hg or below to effectively eliminate atmospheric cushioning.

More about enclosed ballistic ranges

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INSTRUMENTATION

VELOCITY MEASUREMENT

Virtually all ballistic ranges are equipped to measure projectile launch velocity, a seemingly easy task that is fraught with difficulty because of:

    • launch of multiple objects/debris along with the projectile package;
    • luminous and opaque gas cloud around the gun muzzle both ahead of and behind the projectile (muzzle flash); and
    • self luminosity of high speed projectiles in flight.

Further downrange, exact projectile trajectories become hard to control so sensors must accommodate projectile wander.

We at PAI offer velocity measurement equipment with special capabilities that is unavailable from other vendors. The Table below lists equipment we currently offer, tells where it is useful, mentions its operating principle and  indicates its relative cost.

EQUIPMENT

USEFULNESS

OPERATING PRINCIPLE

RELATIVE COST

Continuous X-ray Sensors

Near Muzzle (senses only Proj. Mass)

X-ray beams blocked by projectile mass.

HIGH

Passive Magnetic Detectors

Anywhere Along Trajectory (Senses only moving Magnet aboard projectile).

Magnet aboard projectile induces a signal in a coil surrounding the  trajectory

LOW

Active Magnetic Detectors

Anywhere along trajectory. (Senses only moving electrical conducting  material)

Continuous magnetic field induces Eddy current in metal projectile that is detected by a search coil)

LOW

Laser Ribbon Detectors

Well Downrange from Gun Muzzle (Senses everything larger than 1.0 mm dia.)

Slit of laser light across range trajectory strikes row of detectors.  Light blockage to any detector triggers unit.

MEDIUM-LOW

Hall Type Velocity Station

Well downrange from Gun Muzzle (Photographs everything passing two stations;  Near 100% reliability!)

Projectile images are laid onto moving film via perpendicular-slit Streak  Photography as projectile passes two stations along trajectory.

MEDIUM-HIGH

 

PROJECTILE ARRIVAL DETECTION

Much other instrumentation that provides information on projectile flight and  target impacts needs signals signifying projectile arrival. Often projectile arrival sensors cannot be located at points where signals are needed.  All of  PAI's velocity measurement systems except, Hall Stations, provide electrical signals synchronized with projectile arrival at fixed locations.

VARIABLE FREQUENCY UP/DOWN COUNTERS

PAI has developed a specialized electronic counter that produces up to four  pulses synchronized with:

    • Projectile arrival at any location downrange from two detection stations;  and/or
    • Pulses at user-selected times before of after projectile arrival at a selected points along its trajectory.

More about up/down counters

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