Over 60 years of spaceflight has cluttered Earth’s orbit with debris. How do we track this material, and can we bring it safely back down?

WORDS ALEX DALE

On 4 October 1957, the Soviet Union launched Sputnik 1, the first artificial satellite to orbit Earth. But that historic day also saw another first – the rocket that propelled Sputnik into space detached and became the first piece of space junk. Space junk, or orbital debris, is the common term for any human-made object in orbit which no longer serves a purpose. It ranges from bus-sized items, such as nonfunctional spacecraft, to nuts and bolts and dust from motors. Since 1957, the amount of space junk surrounding our planet has steadily grown, to the point where the US Space Surveillance Network is tracking the movement of more than 34,600 objects five centimetres wide or larger.

While the risk to life on Earth is low, space junk poses a significant problem for craft in orbit. It can travel at up to 17,500 miles per hour, and at that velocity, even a collision with a piece of debris a couple of centimetres wide could be terminal to a spacecraft. To prevent its satellites and spacecraft being damaged, in 2007 NASA entered into an agreement with the United States Strategic Command, which tracks the flight paths of thousands of pieces of debris daily via ground-based radar, as well as lidar that measures distance by illuminating a target with a laser and analyses the reflected light. If the likelihood of a collision is one in 10,000 or higher, NASA is informed and can steer the craft out of the way. The International Space Station has had to make dozens of these evasive manoeuvres since its construction was completed in 2011.