What Goes Up, Must Come Down

Where do satellites go when they die? Operators have two options: let their sputtering Sputniks remain in orbit and become spacejunk, or send them raining down on Earth in a fiery blaze.

Last week, the UK Space Agency chose the cremation option for its UK-DMC-1 spacecraft—one of a group of satellites orbiting the Earth to provide imaging for disaster relief. When the time came to retire the seven-year-old satellite, UK technicians depleted UK-DMC-1’s propellant, bringing it closer to Earth and reducing its chances of blowing up in space. The satellite is still flying around, but it won’t be for long.

The maneuver is the outcome of a growing realization that humans are quickly polluting the outer reaches of Earth’s atmosphere with litter that puts astronauts and expensive spacecraft at risk. The NASA Orbital Debris Program Office estimates that there are some 500,000 chunks of spacejunk 1 to 10 centimeters in diameter orbiting the Earth, and tens of millions of pieces smaller than a marble.

Making matters worse, spacejunk collisions fragment bigger chunks into smaller, less detectable (and thus less avoidable) pieces. Travelling at 17,500 mph, even a tiny speck of paint can gouge a pit half-a-centimeter wide in a space shuttle window.

And as the amount of junk orbiting the Earth increases, so does the risk of crashing into it. The worst spacejunk collision to date occurred last year when a de-commissioned Russian satellite collided with a US communications satellite. And earlier this year, a European Space Agency satellite narrowly missed being bombarded by a 4-ton Chinese rocket booster.

How long the junk remains in orbit depends on how high it is: at 400 miles up, it’ll fall back to Earth within a few years. At 600 miles or higher, the process could take centuries. The UK estimates its methods with UK-DMC-1 shaved a full century off the satellite’s tenure in space.

The international space community is at a loss when it comes to cleaning up the space mess, although suggestions have included using lasers, giant NERF balls, and space tongs. For now, NASA says it’s best just to avoid creating more of it—which means sending the junk crashing back down to earth instead.

Amazingly, although an estimated 12 million pounds of space debris has fallen to earth in the past 40 years, no one has ever reported being harmed by it. A lot of it burns up in the atmosphere, and most of what makes it through lands in the ocean or on empty land (instead of someone’s head).

Space.com has a list of the Top 10 Most Memorable Pieces of Space Junk That Fell to Earth. As space agencies increasingly send instruments like UK-DMC-1 nose-diving through the atmosphere, the list is sure to grow.