Moving and expandable parts of gun consist of pump-tube diaphragm, piston, launch-tube diaphragm, and saboted projectile. As a result of improved piston design, pressure cycle has been significantly improved by smoother buildup, increasing muzzle velocities up to 50%

Teng, R. N.

English

NASA Technical Reports Server

December 1973	 B73-10413 
NASA TECH BRIEF 
Lyndon B. Johnson Space Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Collapsible Pistons for Light-Gas Guns 
.
The problem: 
Hypervelocity light-gas guns have been used to 
simulate the impact of high-speed meteorites on space 
vehicle structures. These sophisticated artillery-like de-
vices have been used for launching projectiles to 
velocities of 9300 m/s (30,000 ft/s), a magnitude 
greater than that of the ordinary artillery piece. A 
typical light-gas gun (see Figure 1) is cylindrical in 
shape and consists of the following: (1) a combustion 
chamber, (2) a pump tube, (3) a high-pressure section, 
and (4) a launch tube. One problem with these guns, 
however, involves the piston in the pump tube. Fre-
quently, these pistons build up pressure either too 
slowly, resulting in low muzzle velocities, or too 
rapidly for safe operation. 
The solution: 
A collapsible piston resolves this problem and in-
creases muzzle velocities up to 14,000 m/s (45,000 ft/s). 
How it's done: 
The moving and expandable parts of the light-gas 
gun (Figure 1) iconsist, of a pump-tube diaphragm, a 
piston, a launch-tube diaphragm, and a saboted pro-
jectile. In operation, a gun-powder charge is introduced 
into the combustion chamber; the chamber is ignited, 
producing hot high-pressure gases. After reaching a
pre-established pressure, these gases burst the pump-tube 
diaphragm, pushing the piston forward. The piston 
moves forward at high velocity and compresses a 
precharged low-molecular gas (generally hydrogen) ahead 
of it. This gas is compressed rapidly, reaching high 
temperatures and pressures that are greater than those 
produced initially in the combustion chamber. Upon 
reaching the specified pressure, the light molecular gas 
bursts the launch-tube diaphragm, exposing the sabot 
behind the projectile. Then both the sabot and projec-
tile are shot out of the muzzle at high velocity toward 
the target. 
The new piston, designed to approximate the ideal 
pressure cycle for efficiency and high projectile velocity, 
is shown in Figure 2. Basically, it consists 1 of forward 
and rear sections and an intermediate collapsible assembly 
having a male member and a female member. Both the 
forward and rear sections are made of polyethylene and 
are conically recessed at the ends. A shear flange on the 
male member has a slightly larger diameter than the 
adjacent cavity, which in turn has a slightly larger 
diameter than the piston section. 
As the gun is fired, the new piston races down the 
pump tube, in the manner mentioned previously, until 
the compressed gas breaks down the launch-tube dia-
phragm. At this point, depending on preselected failure 
strength, the shear flange begins to shear, temporarily 
Pump-Tube	 Pump	 High Pressure	 Piston 
Diaphragm	 Tube	 Section	 (Final Position) 
Projectile 
and Sabot 
	
Piston	 Diaphragm 
Combustion	 (Initial	 .	 Launch-Tube 
Chamber	 Position)	 (Muzzle) 
Figure 1. Light-Gas Gun
(continued overleaf) 
• 
	
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https://ntrs.nasa.gov/search.jsp?R=19730000413 2020-03-17T07:27:47+00:00Z
	Rear	 Forward 
	
Section	 Counterbore	
Shear	
Section 
Flange 0 A), 1 J 
Section A-A	 A	 Piston
Female	 Male	 Section 
Member	 Member 
I' 
Figure 2. Collapsible Piston 
disconnecting the male member from the' female i mem- Patent status: 
ber.	 In	 effect,	 the	 male	 member becomes	 axially This invention is owned by NASA, and a patent 
displaced from the rear member by about 1 cm (1/2 application has been filed. Inquiries concerning non-
inch). A short time later, the female\ member catches exclusive or exclusive license for its commercial de-
up with the male member as the piston section engages velopment should be addressed to: 
the couriterbore further compressing the driving gas. Patent Counsel 
As a result of improved piston design, the pressure Johnson Space Center 
cycle has been significantly improved by smoother Code AM 
buildup, increasing muzzle velocities up to 50%. Houston, Texas 77058 
Notes: Source: R. N. Teng of 
1. Two	 additional	 piston	 configurations	 have	 been McDonnell Douglas Corp. 
developed with similar features and are described in under contract to 
a supporting document. Johnson Space Center 
2. Requests for further Information may be directed to: (MSC-13789) 
Technology Utilization Officer 
Johnson Space Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP73-10413
a 
B73-10413	 Category o7,06 


Collapsible pistons for light-gas guns

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