PARIS — The European Space Agency fired a 7.5-millimeter-diameter aluminum bullet traveling at 7 kilometers per second into a bulletproof-vest-type fabric resembling the outer skin of Europe’s Automated Transfer Vehicle (ATV) to check for space debris resistance.
The resulting damage, shown in photos of the bullet’s exit hole published June 24, illustrates the expected resistance of the ATV and other international space station modules. It also shows the power of a small piece of debris colliding with the space station at orbital velocity.
The 20-nation ESA is scheduled to launch the fifth and last of its ATV freighters to the space station in late July aboard a heavy-lift Ariane 5 rocket. ATV carries water, fuel and other supplies to the station, and also is used as a tug to reboost the station’s orbit, which degrades over time under the effects of atmospheric drag.
While designed to deliver cargo, then to be filled with garbage and subsequently destroyed on re-entry into the atmosphere after several months at the station, the ATV is occasionally used by station astronauts as a sleeping quarters. That, plus the fact that astronauts clamber in and out of the canister to retrieve supplies and store garbage, means the ATV must meet the same debris-proof standards as the station’s habitable modules.
The bullet test was performed for ESA’s Space Environment and Effects section by the Fraunhofer Ernst Mach Institute for High-Speed Dynamics, located in Bruehl, Germany, using a high-performance light-gas gun.
The target was the same multilayer Kevlar-Nextel fabric that protects the other station modules. ESA said that at 7.5 millimeters in diameter, the aluminum bullet would represent “the upper end of the size of debris the shield is designed to cope with. … Testing confirms the spacecraft’s pressure shell would survive such a collision intact.”
The bullet first penetrated the multilayered insulation blanket before going through a 1-millimeter-thick aluminum bumper shield before breaking apart and becoming easier for the deeper layers to handle.
One photo shows the penetration of the deeper layer, a weave of Kevlar and Nextel fabric, which was shredded on impact but afforded enough final protection so that the bullet’s effect on the ATV’s 3-millimeter-thick aluminum wall was no more than a harmless scorching. The shield’s total thickness in orbit is 128 millimeters.
The shielding’s strength is one reason ATVs do not fully disintegrate when re-entering the atmosphere, but break up into pieces that fall into the South Pacific along a corridor that has been cleared of traffic.
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