Over the 50-plus years that humans have been launching objects into space, those objects have left a lot of junk behind. Most fall back to Earth, burning up in the atmosphere, but a lot is still in orbit around Earth.

We’ve learned a lot in that time. Standards have evolved to require “spacecraft and upper stages be designed to eliminate or minimize debris released during normal operations”. Sources of stored energy onboard spacecraft are also required to be depleted or safed as soon as they are no longer needed. This helps to prevent the explosions in orbit, the biggest contributor to space debris.

Debris ranges in size from flecks of paint or bits of metal from a spacecraft to complete non-operational satellites the size of a small truck. About 13,000 known objects larger than 10 centimeters in diameter are tracked via radar and telescopes through the Space Surveillance Network (SSN) operated by the U. S. Air Force. Scientists estimate another 100,000 pieces of orbital debris between 1 centimeter and 10 centimeters are in orbit around Earth along with tens of millions more smaller than 1 centimeters.

On average, orbital debris impacts another object at 22,370 miles per hour, causing a lot of damage. A hit by debris as small as a half an inch traveling at 6 miles per second would be equivalent to a hit by a bowling ball at 300 miles per hour.

All these objects, plus naturally occurring meteoroids, pose threats to astronauts and satellites. Research continues on ways to improve detection of and protection from these objects.

Flight Controllers at NASA’s Johnson Space Center in Houston, Texas slightly alter the path of the International Space Station when larger debris is expected to come within a few miles. The station itself is the most heavily shielded spacecraft created to date. The spacesuits astronauts wear during Extra Vehicular Activities (EVAs) are reinforced with materials used in bulletproof vests to protect from small objects traveling at high speeds, like micrometeoroids.

The Space Debris Sensor (SDS) recently completed functional testing and is awaiting launch aboard a SpaceX launch vehicle to the International Space Station in late 2017. The sensor will be attached to the Columbus module to begin a 2-year mission.

The SDS is a one square meter impact sensor designed to detect and characterize impacts by small debris objects. The sensor combines multiple technologies to measure the time, speed, direction, size, and density of objects down to 50 µm in size, less than the width of a human hair.

Data from this mission will help further our understanding of orbital debris and how to prevent it as well as improve tracking of smaller debris, especially around the International Space Station.

With this information, as well as the orbital position of each detection, the sensor should collect enough data over its intended minimum 2-year mission to update the NASA Orbital Debris Engineering Model for objects smaller than 1 millimeter near ISS altitudes. With lessons learned from the SDS experience, a follow-up mission to place a second-generation sensor at higher altitudes will someday provide the ability to update the risk from small debris to many operational spacecraft in low Earth orbit.