VORTEX GUN AND ITS KIN

The projectile is placed inside a disposable winged sabot which resembles a very slender glider plane. The sabot is propelled by a light gas, preferably hydrogen blowing across a multitude of short wings secured to the sabot. The vortex gun belongs to the transverse gas gun family because the hydrogen flow is transverse to the projectile direction. Many variations of this idea have been proposed, including the spiral gas gun, the vortex gun and the vortex accelerator. Because there is no physical contact between the sabot and the gun, there is no need for tight tolerances. The gun is durable because it operates at room temperature and is free from abrasion and corrosive chemicals. The projectile is exposed to high temperatures, so it is made of a strong tungsten alloy (W-Re-Hf-C). To reduce stress the projectile is supported by the sabot along its entire length. As soon as the sabot leaves the gun, atmospheric drag pulls the projectile out of the sabot. The gas flow is generated either by opening explosively driven gate valves, or by burning a mixture of hydrogen and oxidizer. Oxygen and fine powder of ammonium nitrate are the preferred oxidizers because the products of combustion are free of soot. Ammonium nitrate is hygroscopic, so it removes water vapor produced by combustion. According to Andrew J. Higgins the maximum velocity is about 5 times the speed of sound in the gas. The minimum mass of a steel gun is 1000 tons.

There is no bibliography, but similar ideas are described in:

-Derek A. Tidman and S. A. Goldstein, "Acceleration of Projectiles to Hypervelocities Using a Series of Imploded Annular Plasma Discharges," Journal of Applied Physics, Vol. 51, No. 4, April 1980, pp. 1975-1983.
-Harold E. Gilreath, Robert M. Fristrom, and Sannu Molder, "The Distributed-Injection Ballistic Launcher," Johns Hopkins APL Technical Digest, Vol. 9, No. 3, July-September 1988, pp. 299-309.
-Warren Frisina, "Linear Turbine Spacecraft for Large-Scale Space Development," Acta Astronautica, Vol. 35, No. 1, 1995, pp. 43-46.
-Andrew J. Higgins, "A Comparison of Distributed Injection Hypervelocity Accelerators," AIAA-97-2897, 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, July 6-9, 1997, Seattle, WA.

Lawrence Livermore National Laboratory has been studying the transverse gas guns for a few years and is likely to build a vortex gun accelerating 1 gram projectiles to 15 km/s. Key people involved in the project: Ray Finucane, Harry Cartland, Terry Alger.


SPIRAL GAS GUN

Hydrogen gas flows in two dimensions. Precise timing of the gate valves is critical; a 10-meter long glider calls for 1 millisecond tolerance. The need for a large number of precisely timed gate valves is the only fault of the spiral gas gun.

Spiral gas gun profile

Spiral gas gun profile

Spiral gas gun section

Spiral gas gun section


VORTEX GUN

The vortex gun can be called an improved spiral gas gun. The main advantage of the vortex gun is fewer gate valves releasing the hydrogen gas. Fins located inside the gun force a helical flow of the gas. Interaction between five rows of short wings secured to the sabot and the helical flow of the gas, propels and stabilizes the sabot.

Vortex gun profile

Vortex gun profile (Long guns have more than 2 gas injectors.)

Section of vortex gun 
barrel

Section of vortex gun barrel

The passage of the projectile compresses the hydrogen gas and momentarily heats it up to 660 K, thus raising the speed of sound in the hydrogen to 2 km/s. Some of the drag produced by the nose cone is offset by the forward thrust produced by the tail cone.

Projectile inside sabot

Projectile inside sabot (large image 36k)

The two identical parts of the projectile are joined together by a streamlined crossbar which houses telescoping tubes. A spring twists the two parts slightly when the projectile leaves the gun. The aerodynamic forces produce a torque spinning the projectile about its center of mass. Outside the atmosphere the centrifugal force twists the parts to a position that releases the telescoping tubes, extends the crossbar, and changes the moment of inertia enough to stabilize an apogee rocket motor mounted inside the projectile. See details in umbrella projectile.


To reduce drag, the helical fins may be replaced with pivoting blades.

External injector

External injector

High performance applications utilize pure hydrogen compressed by the two stage light gas gun and offset injector proposed by Andrew J. Higgins.

Offset injector

Offset injector


Andrew Nowicki proposed a sabot with six rows of wings. Andrew J. Higgins likes this idea because the vortex can pump gas away from the central tube, provided that the slits in the tube are narrow. Unfortunately, it is impossible to avoid physical contact between the narrow slits and the wings.

Projectile inside sabot

Projectile inside sabot

Section of vortex gun 
barrel

Section of vortex gun barrel


VORTEX ACCELERATOR

It is possible to combine the powder vortex ram accelerator with the vortex gun. The contraption is called vortex accelerator. Its simplicity makes it the cheapest member of the vortex gun family. A mixture of hydrogen and a fine powder of ammonium nitrate is pumped through the accelerator. Helical ribbons produce vortex flow of the mixture and prevent premature detonation. The vortex generates centrifugal force which keeps most of the powder away from the center of the accelerator. Powder in the center of the accelerator burns before impinging on the nose cone of the projectile and its wings. To prevent fast rotation of the projectile, the vortex alternates between clockwise and counterclockwise direction. The projectile compresses the mixture to the point of ignition and is propelled by vortex flow of the burning mixture. Several rows of flexible wings are attached to the projectile. They are feathered unless gas pressure deflects them.

Vortex accelerator profile

Vortex accelerator profile


The ability to store energy in the gas vortex enables the gun to compete against the orbital coilgun. A glider loaded with cargo enters the gun and generates vortex flow. The energy of the vortex is then used to fire empty glider back to the Earth.