A brief introduction on NASA’s two stage light gas guns

With the increasing frequency of human spaceflight activities,space debris popula-tion is increasing year after year.Nowadays space debris impacts are more and more dangerous to astronauts doing extravehicular maneuvers and to high-pressure vessels and toxic aerospace mate-rials carried aboard spacecraft.The protection strategy against the impact of millimeter space debris is mainly by shielding.In order to design effective shielding for spacecraft and to evaluate the risk posed by debris and meteoroids,we must be able to perform tests in the laboratory. Hypervelocity impact testing has some extreme requirements.The core of the problem is to find a way to launch projectiles at speeds more than seven times faster than the fastest bullet,to measure how fast the projectile is traveling before impact,and to take pictures of impact event that lasts only a few microseconds.Launching projectiles at velocities high enough to simulate or-bital debris impacts requires some remarkable equipment called “two stage light gas gun”.The technology is one of the most important factors in the improvement of experimental ability,and therefore it is considered as a significant indicator to evaluate the experimental level of a laboratory, or even a country.National Aeronautics and Space Administration (NASA),the leading agency in the aerospace area in America as well as in the world,is supported by several laboratories with the ability of performing hypervelocity impact tests,where the two stage light gas guns play a critical role.The White Sands Test Facility (WSTF),located at remote desert foothills of New Mexico,works in close partnership with NASA Johnson Space Center Hypervelocity Impact Technology Facility (HITF).HITF determines the risk of spacecraft posed by space debris,and then designs spacecraft shields based on probability of impact and spacecraft geometry.HITF also builds and sends target shields to WSTF for ballistic-limit,verification testing and accordingly analyzes the results.Other spacecraft materials and components are targeted too,as well as toxic and explosive cargo,including fuel.The WSTF Hypervelocity Impact Testing Program assesses candidate shield materials with the help of two stage light gas guns.These guns shoot projectiles at hypervelocities up to roughly six times faster than the fastest rifle bullet,and mimic the impact of real space debris traveling at even higher speeds.Some other laboratories in America also present a remarkable performance in improving the ability of two stage light gas guns,such as NASA A-mes Research Center,McDonnell-Douglas Corporation,General Motor Corporation,Naval Ord-nance Laboratory,and United States Naval Research Laboratory.