In space, all it takes is a tiny grain of junk travelling at high speeds to create a very, very bad day.

A single sand-sized grain of aluminum ripped this 28 by 12 mm hole and smaller, adjacent holes in this aluminum sheet during hypervelocity collision testing by the European Space Agency. That something so tiny can produce a gaping tear in the thin shell that protects squishy humans from the cold, hard vacuum of space is exactly why the International Space Station adjusted its orbit to dodge away from a piece of space junk earlier this week.

Space is full of junk, and even something as seemingly-benign as paint flecks and dust get decidedly more threatening at hypersonic velocities. Understanding collisions are hugely important to spaceflight, and subject to extensive research with both theoretical models and controlled experiments.

This solar panel on the Hubble Space Telescope was is marred by a 3.5 mm crater around a 0.5 mm hole. Image credit: ESA


The stuffed Whipple shield of layered insulation, aluminum, and kevlar used on ESA’s ATV and the International Space Station from a 7.5 mm impactor travelling at 7 km/s during collision testing. Image credit: ESA/Stijn Laagland

At the ridiculously high speeds in orbit, even something small can cause shockingly damage: satellites are typically pinged by space debris like the test-grain at relative velocities of 10 km/s, while meteoroids can be twice as fast at up to 20 km/s. For context, that’s an order of magnitude faster than a bullet, and a 1-centimeter sphere moving at a relatively modest 10 km/s carries the explosive force of a hand grenade.


While the interior was visibly impacted, the 7.5 mm impactor failed to punch through the Whipple shield during collision testing. Image credit: ESA/Stijn Laagland

The consequence of collisions depends on the materials, their relative velocities, the size of the impactor, and the thickness of the thing being hit. An object just one-third of the target’s thickness can puncture vehicles, tear through solar cells, severe cables, cut through tethers, or be enough to trigger explosive decompression of pressurized containers.


The Hubble Space Telescope’s solar arrays took damage during their 8.25 years in space, including this 2.5 mm hole. Image credit: ESA

For smaller objects or thicker targets, the damage can still be cratering and surface degradation, damaging sensors and denting windows. Collisions also transfer momentum, potentially setting spacecraft off-course, and generate impact plasma that propagates a burst of electronic noise through sensitive instruments.


Even a tiny impactor can create a relatively massive crater. Image credit: ESA

Top image: Result of hypervelocity impact testing. Credit: ESA/G. Porter