Since the beginning of the space age with Sputnik’s launch in 1957, humans have been enthusiastically sending big metal objects into Earth’s orbit. We have made huge strides, but we also made a bit of a mess along the way.
Space debris is like the extraterrestrial equivalent of plastic in our oceans. It sloughs off of human-made objects in Earth’s orbit as a result of collisions or erosion, and poses a risk to any spacecraft that enter orbit. That's why researchers led by Quan Wen of the Air Force Engineering University in Xi’an, China, suggested we might be able to clean them up by blasting them with lasers from a space station.
One centimeter may seem small, but layers of debris in the Earth’s orbit can act like sandblasters to the vulnerable exteriors of spacecraft, especially telescopes and solar panels. It would be similar to scraping sandpaper across your computer screen, except your computer screen is blasting at 17,500 miles per hour through layer upon layer of sandpaper, like the International Space Station.
Each time debris hits new spacecraft, it creates more debris. According to NASA, when a defunct Russian satellite destroyed a working US satellite, the collision produced more than 2,000 pieces of trackable debris.
If this continues, space debris has the potential to increase exponentially. This domino effect is known as the Kessler Syndrome, and was proposed by NASA scientist Donald Kessler in 1978. It suggests a scenario in which the density of space debris becomes so high that each new collision increases the likelihood for another collision. This cascade could clog up the orbit around Earth so much that we wouldn’t be able to use satellites anymore, or send ships into space safely.
No wonder then that Nicholas Johnson, NASA’s chief scientist for orbital debris, said, “the greatest risk to space missions comes from non-trackable debris.”
Wen’s team will publish a paper in Optik - International Journal for Light and Electron Optics this February that seeks to find a solution to this problem. The researchers found that using lasers based in space to blast apart space debris is, theoretically, possible.
Lasers are the most recent in a long line of proposals to get rid of space debris, including using big nets and chasing pieces down one by one. But these methods have criticized as uneconomical.
A laser mounted on a station, on the other hand, can be used multiple times and its operation is simple and relatively low-cost. Lasers can pulse debris into Earth’s atmosphere, where it then burns up.
As to the question of where to put the laser station, some researchers have proposed using a ground-based laser station. One such project was ORION, an Earth-based laser proposed in 1996 to pulse debris out of the sky.
Wen’s team decided to investigate the effects of a space-based station instead. They point out that the operational range of a laser station tethered to Earth would be very limited, while a space-based station has more flexibility, and it would not be as affected by the atmosphere.
“Therefore, it is considered as the most promising approach and is the focus of current research,” wrote the researchers.
Wen and his co-authors presented a model for a space-based laser station. They tested how a laser mounted in space would impact spherical, aluminum debris, and whether different angles made the laser more or less efficient. The debris was modeled in aluminum because it is one of the most common space debris materials, and the sphere shape reduced the complexity of the calculations.
They found that it is theoretically possible for a pulsed laser to ablate the space debris, creating a force that can remove the object from orbit, using a space-based laser. They also found that the laser was more efficient and had better range when the laser was collinear with the debris and had the same inclination, or tilt. In other words, the laser works better when more in line with the debris.
This study offers a promising foundation on which to build a space-based defense against our own pollution. But there are still many hurdles to overcome.
Some writers seem concerned about the potential threat of a world superpower sending a giant laser into the sky above us. For now, though, this model works only theoretically, and is limited to spherical, aluminum debris. It also deals with debris on a case-by-case basis, and would probably not be able to rid the Earth’s orbit of all of its untrackable space debris.
We have a long way to go before we can launch a full-fledged Space Debris Blaster. But it’s a start.