Ordnance – Accelerating
Patent
1993-09-13
1996-01-16
Bentley, Stephen C.
Ordnance
Accelerating
124 3, F41B 600
Patent
active
054838630
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to electromagnetic launchers, and more specifically to electromagnetic railguns, designed to accelerate solid bodies to higher velocities than those of conventional guns.
Electromagnetic launchers have been widely investigated because of the potential to achieve velocities exceeding those that can be practically attained in powder and other thermodynamic guns, in which the maximum velocity is limited by the specific energy of the known propellants. If high enough velocities could be obtained efficiently, electromagnetic launchers would have important military, scientific and commercial applications. The applications include testing and developing new materials, earth-to-orbit launching of materials, such as fuel, building and hazardous materials, and simulation of nuclear fusion impact with velocities on the order of 100 km/s.
The best known and most investigated electromagnetic launchers belong to the railgun family, in which projectiles are accelerated by an electromagnetic driving force applied to plasma or metallic armatures. The armature closes a circuit formed by a pulsed electric power source and a pair of parallel, elongated conducting rails. The power source generates current pulses in the rail-armature circuit. The rails form a railgun bore along which the projectile slides as it is accelerated by electromagnetic forces. U.S. Pat. No. 4,953,441 provides a brief description of the current state of railgun technology and a discussion of potential advantages of railguns with solid armatures.
Early railguns used metal armatures. During acceleration, the metal armatures were heated by the current pulse. If the contact is ideal and the current in the metal armature is distributed uniformly, there exists a theoretical velocity limit due to thermal degradation of the armature material. The theoretical velocity limit for a copper or an aluminum slug-shaped, unloaded armature having a length of about 1 cm is several tens of kilometers per second. The theoretical limit increases proportionally to the armature length. Experimentally, the sliding contact experiences arcing at velocities about or below 1 km/s. No increase of velocity with armature length is found.
In recent years, understanding in the causes of arcing at the sliding contact has revealed two principal causes. First, strong repelling forces between the rails cause the rails to deflect, creating gaps between the sliding armature and the rails. Second, velocity skin effect results in concentration of current near the trailing edge of the contact zone causing thermal degradation of the armature.
The repelling forces are applied mainly behind the armature, but they generate elastic deformations traveling along the rails which may outrun the armature and deflect the rails. To avoid the gaps and to maintain a tight contact, the rail deflections should be minimized. Prior teachings suggest increasing the stiffness of the railgun barrel structure to withstand the repelling forces. Techniques have been developed to provide for sufficient structural stiffness of barrels, resulting in a high barrel mass per unit length.
Even with stiff barrels, metal armatures should be designed to maintain the electromechanical contact during the launch. Armatures are usually inserted in the bore with substantial interference. Elastic, magnetic or inertial forces are often used to maintain pressure at the contact. Although a variety of armature designs have been developed and tested, maintaining a reliable contact, especially at the elongated contact zone for launching massive payloads to high velocities, remains a problem.
Moreover, if the sliding contact pressure occasionally becomes too high, gouging may occur. Excessive contact pressure may occur when the projectile begins to ballot within the bore. Further, high current density at the sliding contact causes superheating which degrades the mechanical properties of the armature and rail materials near the contact, which facilitates gouging. Gouging may greatly
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Bentley Stephen C.
Dyuar Incorporated
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