Before anyone tells you otherwise, you’re not going to get clobbered by a satellite on Sunday. Not that a satellite isn’t coming; it is. It’s called GOCE (GO-chay), for Gravity Field and Steady State Ocean Circulation Observer—which is why its friends prefer a simple GOCE—and it’s currently only 105 mi. (169 km) up and descending fast. The satellite, launched in 2009 by the European Space Agency, makes a single orbit of the Earth once every 88 minutes—an important two minutes faster than the standard 90 minutes most spacecraft take. In the orbital biz, faster equals lower, which equals faster still and lower still, until, well, boom.
So how worried should you be? Not much more than a tiny bit (which is admittedly shy of a more-reassuring not at all). For starters, 70% of the Earth’s surface is water, meaning there’s only a 30% chance of the satellite debris hitting a landmass. What’s more, the overwhelming percentage of the human population lives on only a small share of that land—in some countries, as little as 3% of the square mileage is occupied. So a satellite would practically have to be aiming at your house to strike it.
What’s more, while GOCE weighs about a ton, most of that mass will break up and vaporize on the way through the atmosphere. A maximum of 45 pieces are predicted to survive, none more than 200 lbs. (90 kg), with a ground footprint no greater than 190 sq. ft. (18 sq m) for the whole mess.
None of that is to rule out all risk. A 200 lb. slab of molten metal crashing through your living room ceiling would be a very bad way to start a Sunday morning. The same piece of ordnance landing in, say, Times Square or a packed Soldier Field would be a bigger problem still. But that won’t happen. Really. (Probably.)
What’s more, space junk is something we ought to be used to by now. About 100 tons of material rains down on us every year, though most of it is dust and meteors—and the overwhelming majority of that never reaches the ground before being incinerated in the atmosphere. Spacecraft come down more than you think too. In 2011, a NASA atmospheric satellite splashed into a desolate patch of the Pacific Ocean; that same year, a Mars-bound Russian probe that never made it out of Earth orbit hit the Pacific too, west of Chile. Ditto the Russian Mir space station in 2001—another Pacific burial, this time near Fiji. See the pattern? The biggest ocean has the greatest chance of taking the most hits—and it does. Of the major satellite crashes, only NASA’s Skylab made landfall, scattering parts of itself across the Australian outback in 1979.
The reason for all this crash-and-burn is that orbits aren’t forever. Even in the seeming vacuum of near-Earth space there are wisps of atmosphere drifting up, dragging at a spacecraft as it goes by and slowing it down by the tiniest amount. Over time—and orbiting ships have nothing but time—that proves fatal. Low-orbit spacecraft that have to stay up indefinitely or at least for many, many years need periodic boosts from on-board engines to nudge them up a bit.
The very highest satellites—the ones called geosynchronous, since their 24-hr. orbit matches Earth’s rotation making them seem to hang in one spot over the ground at all times—top out at around 22,000 miles up (35,000 km). Above that? The graveyard orbits. That’s where satellites that have passed their useful life and are too cumbersome to bring down are parked in a sort of orbiting necropolis, where they’ll linger for centuries—though those orbits too will eventually decay. GOCE could not be boosted because it has only a small, putt-put ion engine aboard it, which is great for making fine trajectory tweaks, but terrible for putting any muscle behind the ship.
While all of this makes a lot of people uneasy, it’s pretty much the cost of doing business in the 21st century. You can have global communications, satellite weather forecasting, satellite TV, Google Earth, global cell phone coverage, live coverage of the Olympics on every continent—or you can have debris-free skies. So fire up the iPhone, flick on the football game and buy a hard hat if it makes you feel better. Either way, GOCE’s coming home.