Who's going to fix the space junk problem?

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of "Ask a Spaceman" and "Space Radio," and author of "How to Die in Space." Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

There are over 20,000 known and tracked pieces of space debris orbiting Earth, each one traveling at about 15,000 mph (24,000 km/h). They pose a risk to future space missions, and nobody is bothering to clean it up. Why? Because it's too hard.

In the early 1960s, the U.S. military wanted to devise a new way of communicating with its forces around the globe. If an enemy severed undersea cables, they could only rely on bouncing radio signals off of the ionosphere, which was an unreliable method. The Cold War-era solution? A program called Project West Ford, a plan to launch 480 million tiny slivers of copper needles into space, giving Earth an artificial ionosphere and a reliable way to communicate.

After the first batch was successfully launched, however, the program was canceled. One reason was the accelerated development of communications satellites. The other was that everyone realized that sending countless bits of random junk into space was probably a bad idea.

Related: How do tiny pieces of space junk cause incredible damage?

Since then, the amount of space junk has only grown. In Earth orbit, there are more than 23,000 objects larger than about 4 inches (10 centimeters), another half a million objects larger than about 0.4 inch (1 cm) and possibly 100 million more smaller than that, according to NASA. And there's all sorts of stuff up there: dead spacecraft, spent rocket boosters, lost gear from space missions (including a glove, a camera, a blanket, a wrench and, somehow, a toothbrush), random bits of wrecked gear, paint flecks, bits of metal, frozen propellant, and a lot of screws and bolts.

Space is getting messy, and it's making life dangerous.

Incoming!

On April 24, 1996, the U.S. Ballistic Missile Defense Organization used a Delta II rocket to launch an infrared monitoring satellite into orbit. About a year later, Lottie Williams of Tulsa, Oklahoma, was minding her own business in a park when she was struck in the shoulder by a 6-inch-long (15 cm) piece of fiberglass and aluminum. Minutes later, more pieces of the second stage of that Delta II rocket crashed a couple hundred miles away.

Williams became the first (and so far, only) person to be struck by falling space junk. But an estimated 100 tons of space junk makes it to Earth's surface every year (though most of it falls into the ocean and does not pose a risk to humans).

Related: How are asteroids, space weather and space debris detected before they hit Earth?

And there's more. In 2007, China tested its anti-satellite technology, hurling a massive, hypervelocity slug at a weather satellite. The test worked — and created more than 3,000 pieces of tracked junk in orbit. In 2009, a (functional) Iridium communications satellite was supposed to sling silently by a (dysfunctional) Russian military Kosmos satellite with almost 2,000 feet (600 meters) to spare. It didn't, and that one event triggered another avalanche of 2,000 debris objects.

About once a year, the International Space Station has to maneuver to avoid a dangerous piece of junk while the astronauts hide in safety in a Soyuz capsule. The space shuttle famously collected holes and craters in its windows, radiators and thermal tiles from collisions with … mostly paint chips.

Despite their small size, the incredible velocity of space junk objects gives them a serious punch, creating a very real risk to future space missions. With the launch of megaconstellations of broadband internet satellites from the likes of SpaceX, OneWeb and Amazon, many rightly fear the coming of "Kessler syndrome," when enough debris causes enough collisions to trigger even more debris, cascading to the point that Earth orbit is an unsafe, unusable wasteland.

Laser brooms, boosters, nets and harpoons

Unfortunately, private companies and national governments are slow to act. Most of the efforts focus on mitigation and avoidance of generating space junk in the first place. For example, rockets have to use up all of their fuel and reactants, to minimize the risk of an unexpected explosion. And when satellites reach the end of their lives, they can either deorbit and (hopefully) burn up in the atmosphere or, if they're high enough, push themselves into the "graveyard orbit" hundreds of miles above anything useful.

While these mitigation strategies may help control the spread of space junk, they don't do anything to clean up what's already up there. Earth's own atmosphere will do some of the work as it drags down on anything in low Earth orbit, but depending on the orbit, that process can take anywhere from a few months to a few decades.

Space agencies and private companies have come up with a variety of cleanup ideas. Special missions could push other satellites down into the atmosphere or up into the graveyard, using technology as old as civilization itself: harpoons and nets. Other plans call for ground-based lasers to heat up one side of a satellite, causing it to shift its orbit and get caught in Earth's atmosphere.

But besides the ground-based laser, amusingly nicknamed a "laser broom," all of the proposals call for launching new satellites, thus making satellite cleanup uncomfortably expensive. Besides, there's also the fact that any "satellite cleanup" technology automatically becomes a "remove an enemy's satellite from the sky" technology. This means that any proposal quickly moves into the murky waters of defense, international diplomacy and the militarization of space.

For now, our best strategy is to track, monitor and warn, using a network of ground- and satellite-based observatories — and cross our fingers.

Learn more by listening to the episode "Who is going to clean up all that space junk?" on the "Ask A Spaceman" podcast, available on iTunes and askaspaceman.com. Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.