A few decades ago, the space around Earth was empty. It’s very much not empty anymore with a multitude of satellites and an operational International Space Station. The space around Earth is also home to many years worth of abandoned satellites, rocket boosters, and other bits of debris flying around at incredible speeds. All that space junk has become an increasingly serious problem, as even a small impact can completely destroy a working satellite or spacecraft. Now, NASA is using the ISS to gather more data on the behavior of space debris in hopes of developing better defenses.
NASA and other space agencies keep tabs on larger pieces of space junk that are a few centimeters to a few meters in size. An impact with one of these would be catastrophic, and there’s not much we can do about that. The crew of the International Space Station (ISS) has even had to take cover in the station’s Soyuz escape pod a few times when there was a threat of impact. However, there many smaller piece of debris — like paint chips, small screws, and tiny meteorites — that are harder to track. These are between 50 micrometers and 1 millimeter in size. The effect of those impacts is what NASA wants to study with the Space Debris Sensor (SDS).
NASA delivered the SDS to the station earlier this year, and it’s now installed on an external payload site that faces the station’s vector of velocity. It’s an impact sensor, so the goal is to make sure anything that hits the SDS has as much relative velocity as possible. The SDS is about 1 meter square (a little over 10 square feet) in size. The surface is a thin layer of Kapton, a polyimide film that remains stable across a wide range of temperatures. Below that is a separate layer of Kapton, this one with embedded acoustic sensors and a grid of resistive wires. The top two layers are there to be punctured, but behind the Kapton is backstop with additional sensors.
When a piece of space junk hits the surface of the SDS, the acoustic sensor registers the time and location of a penetrating impact. The resistive grid can estimate the size of the impactor from changes to the resistance of the wires. Those backstop sensors measure the size of the hole in the upper Kapton layers to work out the velocity at which the object struck the surface. Based on this data, researchers should be able to tell if the impactor was a natural bit of space dust or a piece of some long-forgotten space mission. Data will be related to scientists on the ground, where hypervelocity tests can be carried out under controlled conditions.
The SDS project will improve safety on the ISS as well as other manned missions. We just don’t know enough about the effects of small impactors, but the SDS could help in the design of new safety procedures and even new materials that can survive a micro-impact.
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