Light gas cannon
A light gas gun (engl. Light gas gun or light gas gun ) is a mass accelerator u. a. in the experimental Impaktphysik is used projectiles to accelerate to high speeds. It is between one-stage light gas guns (engl. Single-stage light gas gun ) and two stage light gas guns (engl. Two-stage light gas gun ) distinguished. Often light gas cannon and two-stage light gas cannon are used synonymously.
idea
The maximum speed of objects (generally " projectile ", English. "Projectile" or "model") with the propellant charges are accelerated, u. a. limited by the maximum speed of the propellant gases. The idea of a light gas cannon is therefore to use a very light molecular gas as the propellant for acceleration, i. A. Helium or hydrogen is used. With the same kinetic energy , its particles can be accelerated to a higher speed than the relatively heavy combustion gases of a propellant charge. Light gas accelerators therefore enable a comparatively high final velocity of the projectile.
For comparison: the molar mass of molecular hydrogen (H 2 ) is approx. 2 g / mol, while the products of conventional propellant charge powder (a mixture of water , carbon dioxide and nitrogen ) have an average molar mass of approx. 30 g / mol. Conventional cannons reach speeds of up to approx. 2.8 km / s, while two-stage light gas cannons reach speeds of up to approx. 11.5 km / s.
construction
The main parts of a two-stage light gas cannon are the propulsion tube (English. Pump tube) and the barrel (English. Launch tube). The light gas is located in the propulsion pipe and is compressed by means of a cylindrical piston . The piston is usually driven by a propellant charge or a compressed gas . Between the propulsion tube and the barrel there is a conical so-called high pressure section, the end of which is separated from the barrel by a valve. When the light gas has reached a sufficiently high pressure, the valve is opened and the highly compressed light gas flows into the barrel and accelerates the projectile. A metal disc between one and five millimeters thick, which is provided with slit or cross-shaped predetermined breaking points (petal valve) and which bursts at a certain pressure, is usually used as the valve. In the high-pressure section, extremely high pressures of the order of 1 GPa or 10,000 bar are briefly reached. The compression of the light gas represents the first stage, the acceleration of the projectile the second. Hence the name two-stage light gas cannon.
If the end of the high-pressure part is also designed as a nozzle , as shown in the adjacent illustration , the effect is further enhanced.
Single-stage light gas cannons consist of a reservoir with an attached barrel. The reservoir and barrel are initially separated by a membrane. Plastic membranes are mostly used here. After the projectile has been introduced into the barrel, the reservoir is filled with molecularly light gas using pumps. When the desired reservoir pressure is reached, the membrane z. B. burst with a thorn. The gas flows into the barrel and accelerates the projectile.
- Projectiles / sabot
The projectiles are not fired directly. Instead, they are embedded in so-called sabot (as is sometimes referred to as “sabot” in English and French). The sabot, mostly made of plastic, breaks up into several elements when it leaves the barrel and is caught by a screen (sabot catcher). The separation is usually achieved aerodynamically, either by a high gas pressure outside the barrel or by the pressure of the propellant gas.
This technique has the advantage that projectiles of almost any shape can be fired, e.g. B. Models for space debris or meteorites , rod penetrators ( impact projectiles ) with aerodynamic stabilizers. In the event of missed shots, the sabot already separates in the barrel and releases the projectile. Such cases lead to severe damage, which usually makes the barrel unusable.
Uses
Light gas cannons are mainly used for high speed impact tests. The aim of such attempts is to understand the physical processes involved in impacting z B. of mini meteorites in space vehicles and satellites or of projectiles in armor to investigate. Such experiments also serve as model experiments to understand meteorite impacts on Earth. After leaving the barrel, a projectile flies through the so-called blast tank, in which the propellant gas is intercepted. The mentioned aperture is also located here, as is usually several laser light barriers that are used for speed measurement and as a trigger source for the sensors. The blast tank is followed by another chamber, called the impact tank or target chamber, in which the target is located. Both tanks offer the necessary splinter protection through appropriate armoring and are evacuated if necessary (high speeds, hydrogen as propellant gas) . Impact tank or target chamber are equipped with sensors (such as high-speed cameras , X-ray tubes and films, etc.) in order to observe the impact (" impact ") on the target . The impact process often only takes a few tens to hundreds of microseconds.
In the early 1990s, the American Lawrence Livermore National Laboratory used light gas cannon technology in the Super High Altitude Research Project (SHARP). This space cannon project was supposed to transport payload into space at one twentieth of the previous cost using rocket technology. In the tests, speeds of 3 km / s were achieved with 5 kg projectiles. The next stage of development, which would have made kills into space and cost US $ 1 billion, was no longer approved in 1995. In the meantime, the company Quicklaunch, which was spun off from the SHARP project, is trying to further develop light gas cannon technology in order to commercialize it for transporting payloads into space. The aim is to be able to carry a payload into space for $ 1100 / kg. Since the escape speed from the earth is 11.2 km / s and a muzzle speed of 6 km / s is aimed for for the quick launch light gas cannon , the concept includes an additional rocket stage.
power
The highest speed achieved so far with a two-stage light gas cannon is around 11.5 km / s
. With shots over approx. 8 to 9 km / s, the wear on the system increases significantly, so that from approx. 10 km / s the barrel and high-pressure part usually have to be replaced after each shot. Because of the cost involved, such shots are rarely performed. In addition, so far only short plastic cylinders have been accelerated to maximum speed.
The speeds routinely achieved with two-stage light gas cannons depend on the mass of the bullet. In the milligram range , approx. 10 km / s (36,000 km / h) are achieved, in the gram range approx. 7 km / s (25,000 km / h), in the kilogram range approx. 5 km / s (18,000 km / h). For orientation: In the simulation of space debris -Einschlägen be balls of aluminum having a diameter (about 1.4 g) Missed between about 1 mm (about 0.0014 mass g) and 10 mm.
The speed can be adjusted via the amount of propellant charge and the light gas pressure in the pump tube for the respective projectile mass.
Single-stage light gas cannons achieve considerably lower speeds.
However, there are improvement concepts that promise an increase of up to 15 km / s, so the light gas cannon technology is not yet exhausted.
Similar technologies
Voitenko compressors, a design based on shaped charge technology, use hydrogen gas to accelerate thin disks (similar to sabot projectiles ) to up to 40 km / s. For example, hydrogen gas was accelerated to 67 km / s with a 66-pound shaped charge in a Voitenko compressor consisting of a 3-cm glass-lined tube 2 meters in length. The apparatus is destroyed in the detonation , but relevant data can be extracted beforehand.
See also
Web links
- NASA light gas cannon ( Memento from December 13, 2016 in the Internet Archive )
Individual evidence
- ^ Charlene Crabb: Shooting at the moon . In: newscientist.com (Ed.): New Scientist . No. 1937, August 6, 1994. Retrieved December 29, 2011.
- ^ SHARP in the Encyclopedia Astronautica , accessed December 30, 2011 (English).
- ↑ David Shiga: Blasted into space from a giant air gun ( English ) newscientist.com . October 7, 2009. Retrieved December 21, 2011.
- ↑ TW Alger et al: Direct Energy Exchange Enhancement in Distributed Injection Light Gas Launchers ( English , PDF; 500 kB) Lawrence Livermore National Laboratory . April 6, 2000. Retrieved January 9, 2012.
- ↑ Explosive Accelerators " Voitenko Implosion Gun "
- ↑ NASA " The Suicidal Wind Tunnel "
- ↑ GlobalSecurity " Shaped Charge History "