Europe's Space Agency Is Investigating Why Satellites Tumble to Their Deaths

The need to clean up space junk from our ever-more crowded orbit has resulted in some memorable plans—Australia's space lasers, Switzerland's satellite claws, harpoons, and even kamikaze robot janitors—but the European Space Agency's next step feels like the most practical. Maybe we can prevent more space junk by just figuring out why satellites go into death tumbles in the first place.

Once they reach the end of their lives, satellites are supposed to be sent into a higher “graveyard orbit,” 186 miles above where functional satellites are orbiting.

But, more often than you might think, satellites have mucked up in one way or another, leaving their caretakers on Earth to watch helplessly as the satellites tumble towards Earth, or worse, stay in orbit as a hazard to other satellites and the International Space Station.

There are plenty of high-profile examples: Russia’s Phobos-Grunt spacecraft was supposed to go to Mars, but its rockets didn't fire as scheduled and it plummeted back to Earth in early 2012; Germany’s ROSAT stopped working in 1998, was decommissioned in 1999, but didn't make an uncontrolled return to Earth until 2011; a month earlier, NASA's Upper Atmosphere Research Satellite capped off a 20-year tenure in space by falling back to Earth.

Despite being against the rules, not making it to graveyard orbit appears to be the rule, not the exception. According to a study in Advances in Space Research, just a third of the 103 spacecraft in geostationary orbit that reached the end of their life between 1997 and 2003 made it to graveyard orbit.

Whether they're launches that have gone awry, or satellites that experience unexpected failures in orbit, the ESA says that “in every case, the satellite has been seen to be tumbling—but the reason why remains a mystery.” The long list of potential perturbations includes "changes in the satellite's centre of gravity as parts break off, atmospheric drag, the faint but steady push of sunlight, micrometeoroid and debris impacts, internal magnetic fields, outgassing and fuel leaks, exploding batteries and even the sloshing of leftover fuel," the ESA stated.

Before netting, grabbing, or shooting down an unused satellite—even if you just want to predict where it will land—you have to understand its tumble. The ESA's new program, announced today, will “combine detailed computer analysis with a range of ground-based observations,” which means they'll be bouncing lasers off of satellites' retroreflectors from a “global network of ground stations.”

A press release announcing the program stated that “laser ranging can pin down a satellite’s position to within centimetres, but has seldom been attempted on out-of-control objects.”

That's not the only unusual tack being taken here: While most satellite monitoring is done from optical telescopes and ground radar, the study is going to investigate the potential of using optical and radar satellites in orbits near the tumbling satellites for “space to space observations,” which could just as easily be described as hot “satellite on satellite” action.

There are more than 12,000 orbiting items in total being regularly tracked by the US Space Surveillance Network today, and 38 percent of them are decommissioned satellites. With space junk now a confirmed Academy Award-winning threat, the need the clear the sky feels more pressing than ever. The next step is figuring out why satellites end up as junk in the first place.