In the movie Gravity, Dr. Ryan Stone (Sandra Bullock) and Matt Kowalski (George Clooney) are astronauts performing a space walk outside Space Shuttle Explorer, working on the Hubble Telescope. The plot of the movie quickly thickens when Mission Control notifies them that an attempt by the Russians to decommission a satellite by a missile strike has gone terribly wrong, causing significant space debris that puts their team at risk. Quite an interesting turn of events for a storyline; however, much of NASA’s real-life story of satellites, vehicle bodies, space suits, etc. includes the risk from space debris impact. Debris can be quite small to the eye, yet still pose a danger to real-life astronauts performing space walks, with the debris travelling at hypervelocity speeds in excess of 2 kilometers per second. In comparison, a small arms round can reach nearly 1.5 kilometers per second, not quite reaching the low end of the hypervelocity rate.
So how does NASA protect astronauts and space assets from being compromised by space debris? The obvious answer would be to make every outer shell of anything going into space able to take a hit like an M1A2 Abrams. The reality is, though, every ounce of weight counts, thus requiring scientists and engineers at JSC’s Hypervelocity Impact Technology Facility (HITF) in Houston to determine the risk posed by space debris and to develop innovative protection that is as light as possible yet still able to take an acceptable hit from space debris without major compromise to the internal product being protected.
Once a targeted material reaches a point where it is ready for impact analysis, HITF personnel team up with White Sand Test Facility’s (WSTF) Hypervelocity Impact (HVI) test team for ballistic testing. The Hypervelocity team, including ERC’s finest, assesses the protective armor by using two-stage light gas guns (LGG). Each gun discharges projectiles at hypervelocity rates up to 24,000 feet per second, 24 times faster than the speed of sound. These shot rates represent the likely impact of real space debris traveling at even higher speeds.
At the LGG facility, there are 1 inch, .50 caliber, and .17 caliber guns. Firing these guns requires an extreme amount of energy release, thus requiring the facility to be remotely located, housing underground bunkers and following access control protocol.
The two-stage gun uses standard smokeless gunpowder as its first stage and highly compressible gas for the second-stage to launch the projectile package. The smokeless powder charge sends a polyethylene piston at 2500 feet per second down the pump tube, compressing the hydrogen gas. The piston enters the tapered high-pressure coupling section and deforms in a rapid energy-absorbing stop, capturing the internal pressurization. At this point, a stainless steel petal-valve ruptures, accelerating the launch package down the barrel. At the expansion chamber, hydrogen collects and dissipates, allowing a stripper plate to separate the sabot from the projectile in free flight.
Various high speed cameras are used, some capable of 100 million frames per second, to capture the target impact and debris cloud. Because of the speed of the projectile, measuring the velocity requires the use of laser intervalometers (automated shutter devices). The data acquisition must operate at a greater bandwidth to capture the diagnostic information from the light detectors and temperature, pressure, and shock measurement equipment.
Once the shot is complete, the gun is processed for future use and the data is compiled for analysis. To better understand the process, take a moment to watch the NASA 360 video: