In Need of a Space Clean-Up
Space debris just keeps on coming and coming and coming. Is anyone ever going to clean it up?
On a bright sunny day beyond the city, you can gaze at the sky and witness its blue hue. By night, you may see the constellations. Before your very eyes — and you won’t see this — lies a junkyard of orbiting debris with a total weight of 6,000 tons. This kind of space junk did not come from fly-by meteors; it came from humans and all their missions to space.
For about six and a half decades, we have sent all sorts of devices into space: rockets, telescopes, and communication satellites. Aerospace engineers built these technologies to withstand space, but just as a cell phone is a potato after so many years, so will these space technologies become decommissioned and be rendered useless. In such a case, one of two things can happen. Either the engineers will use the remaining fuel in the satellite to slow it down to de-orbit into the atmosphere, where fiery cooking awaits to consume it, or they force it farther into space. The latter is particularly more feasible for satellites in farther orbits around the Earth, where trying to steer it back home costs too much fuel. Deemed the graveyard orbit, a satellite would get redirected to an orbit 22,400 miles away from Earth. (That’s a safe 200 miles away from the farthest active satellite.) As for close-enough satellites that do not fully burn up in the atmosphere, there’s the Spacecraft Cemetery in the Pacific Ocean for them to land. It’s the farthest point from any human civilization.
These protocols for dealing with inactive satellites take time, resources, and attention. Typically, an outgoing spacecraft can launch with collision trajectories in mind, but the matter worsens with space debris on a smaller scale. The Department of Defense’s global Space Surveillance Network (SSN) sensors have tracked over 27,000 bits of space junk. More than 23,000 pieces of debris are the size of a softball, over half a million resemble the size of a marble, and about 100 million pieces take up the space of three grains of salt. The microscopic scale need not be brushed off, for orbiting space junk can travel up to 17,500 mph. Even a fleck of paint can damage a spacecraft and bring hell to its windows at that speed. These millimeter-sized orbital debris pose the most threat to ending the mission of robotic spacecraft operating in low Earth orbit (LEO).
Some catastrophes have already taken place from the space debris problem. In 1996, a French satellite was damaged by the remaining flings of a French rocket explosion from a decade prior. And since then, the debris count has only gone up. In 2007, China’s anti-satellite ballistic missile to its Fengyun-1C weather satellite increased the number of trackable space junk by 25%. Two years later, a decommissioned Russian spacecraft collided with and destroyed the active US Iridium commercial satellite, adding upwards of 2,300 pieces of large, trackable debris and plenty of smaller pieces to the space junk population. That day, February 10, 2009, marked the first-ever accidental collision between two in-orbit satellites. In just two years, that’s a total jump of 70% in space debris.
All that space junk can eventually lead to more space junk. Take, for example, an orbit explosion. It can occur from remaining fuel in places like tanks and fuel lines of an intact rocket stage/satellite. Space conditions can weather the infrastructures of these discarded lumps of metal and lead to leaks or fuel mixing that could trigger self-ignition. The aftermath explosion destroys the remaining spacecraft and scatters its pieces every which way at various velocities. As for debris that doesn’t come from fragments of a spacecraft’s structure, solid rocket-motor firings such as aluminum oxide (Al2O3) also become space junk in the millimeter-to-centimeter size range. At this rate, we are approaching Kessler Syndrome, in which space junk gets so cluttered that debris continues to self-populate from the constant collisions. If we continue to fire away spacecraft with no afterthought, we’ll get to Kessler Syndrome all right. If we halt space exploration henceforth, collisions between existing satellites would still contribute to more space debris than can be removed from atmospheric drag. In other words, we must do something about our junkyard parked beyond the clouds.
Fortunately, space debris removal projects are already underway. NASA’s Johnson Space Center has developed an Active Debris Removal Vehicle (ADRV) that can remove large orbital debris from LEO. The system is an efficient and effective solution to handling large space junk occupying LEO, such as rocket stages and decommissioned satellites. It uses three essential technological features: a control system for navigation and control throughout the mission, a debris object characterization system for detecting debris motion, and a capture and release system for latching onto the body. Similarly, NanoRacks-Remove Debris provides a means of dealing with space junk through capture. It uses a 3D camera to detail the environment and approaching debris and deploys a net to capture and de-orbit trash up to 1 meter in size (Note: these observations come from a recent experiment).
There are no international space laws concerning a clean-up in space, mind you. In a worst-case scenario, all the debris collisions in space will damage satellites used for the Internet, email, GPS navigation, and mobile phone usage. By then, we can forget about going to Mars and count ourselves lucky if we reach the moon again.
