Why This Destroyed Spacecraft Shield Is a Good Thing

Pretty much everything in space is a hazard. Even the smallest pieces of debris, like micrometeoroids, can be fatal. That’s why scientists develop specialized materials that protect manned and unmanned spacecraft from impacts, then shoot tiny pieces of debris at them to prove they really will work in space. The European Space Agency released an image showing the results of such an impact test two weeks ago, and though it looks terrifying, it’s actually proof that the high tech space shields work as designed.

ESA recently tested how Kevlar-Nextel fabric, a multilayered shield that’s in use on its Automated Transfer Vehicle, would withstand a high speed micrometeoroid impact in orbit.

Since 2008, ESA’s ATV has been instrumental in keeping astronauts on board the International Space Station supplied with anything from food and water to hardware and spare equipment. To keep the spacecraft and more importantly its cargo safe from impacts in space, the vehicle is fitted with a “whipple shield.” Invented by Fred Whipple in the 1940s, whipple shields are a type of hypervelocity impact shield that use an outer bumper set away from the wall of the spacecraft. The outer bumper is designed to absorb the immediate force of an impact, dissipating the projectile’s energy and breaking it into pieces such that the remaining structure that hits the impact is harmless.

ESA’s recent impact test was done using a version of the whipple shield called a “stuffed whipple shield.” This is a multilayered version of the whipple shield that has filling interspersed between rigid layers. In the case of the recent ESA impact test, the stuffed whipple shield was made of Kevlar and Nextel, a ceramic fabric that has been instrumental in creating durable low weight impact shields for spacecraft. Kevlar-Nextel shields are among the most effective, light-weight shields against space debris, and are far more effective than single thick aluminum shields.

The five-inch thick Kevlar-Nextel shield used in ESA’s recent test was hit with an aluminum bullet 7.5 millimeters (slightly less than 0.3 inches) in diameter traveling at 4.3 miles per second. The bullet pierced the multilayer insulation blanket before reaching the 1 millimeter (less than 0.03 inches) thick aluminum bumper shield.

As designed, the double-walled shield breaks projectiles apart on impact. During ESA’s recent test, the aluminum bullet broke up into a cloud of metal fragments and vapor that were more readily stopped and deflected by subsequent layers. The layer of stuffing, which is made of woven lightweight Kevlar and Nextel fabric, further slows the incoming debris. That fabric was completely shredded by the tiny projectile, but it successfully absorbed the mass and energy of the projectile enough that what remained of the bullet harmlessly scorched the 3 millimeter (about 0.11 inch) thick inner aluminum wall.

So while it might look terrifying that the outer layer of a spacecraft shield is ripped apart and burned, it’s actually a good thing. Far better to destroy the outer shield than the spacecraft wall.