Space Junk? Space Lasers!
Let’s clean up our orbit.
Space is a wonderful and inspiring place. Dotted by an infinite smattering of of stars, galaxies, planets and moons, space has long inspired our species to look upwards in hopes of a grander, more prosperous future. For Millennia, the looming enormity of the cosmos has reminded our species of just how small our world really is, and how much of the universe we have yet to discover. Then, in 1957, humanity launched its first orbital object into space: Sputnik 1. It was at this moment that our race finally glimpsed the true potential of space as a manipulable environment. No longer was space just an impermeable spectacle above us; it was our future. In the ensuing decades, technologies were deployed into orbit around the Earth which allowed faster and more wide spread communication, global data linkage, more accurate climate studies, precise location tracking, robust defense and security systems, and so much more. The more we learn about space, the more we realize how much the entire future of our civilization depends on it.
But that future is under siege. In our very own pursuit of this endeavor, we have left our orbit shrouded in a deadly swarm of man-made orbital debris, known as space junk, which is putting a dangerous strain on future space-bound missions. This junk consists of everything from shards of solar panels, to astronauts’ lost tools and equipment, and even entire defunct satellites, all large enough to cause critical damage to any satellite, spacecraft, or space station in the event of a collision. Due to the debris’ vast degrees of differing orbital characteristics, collision speeds between pieces of space junk and an orbiting spacecraft can exceed 15 km/s, meaning that even a stray fleck of paint can impact with as much energy as a baseball travelling at the speed of sound. NASA estimates that there is upwards of a million chunks of space debris larger than a centimeter in orbit of our planet right now, and the problem worsens every year. Collisions between pieces of orbiting debris result in the creation of even more space junk, feeding a positive feedback loop that, if left unchecked, could make launching spacecraft of any kind into orbit impossible within the next century.
Since the conception of this “Kessler Syndrome”, a slew of creative ideas have been fronted to combat the growing issue. Most ideas involve the removal of large debris via specially designed space nets. Large pieces of space junk represent the most critical aspect of the problem because they have the potential to be shattered into the highest number of smaller pieces, which are more difficult to track and predict. In theory, a spacecraft equipped with a launchable net on a tether could “grab” a derelict satellite or chunk of debris, then deposit it at a lower altitude where atmospheric drag is high enough to decay its orbit in a matter of months. Though a novel solution, the space net suffers from a couple key drawbacks. The net, restricted in volume, and the spacecraft, restricted by fuel, could only transport a few pieces of debris at a time, and would inevitably only deorbit a modest handful of of junk before the spacecraft itself would become part of its own mission. Also, though ridding of large space junk is incredibly important, it is noteworthy that this type of debris only represents a meager 0.026% of the problem. As discussed previously, a fleck of paint is nothing to ignore.
Clearly, a more effective solution is needed for the remaining majority of orbital space junk. Regan lovers, James Bond fans, and sci-fi nuts unite: the space laser may be our last, best hope for space travel! In this idea, a satellite or a fleet of satellites equipped with powerful lasers would work to deorbit space debris by imposing radiation pressure on them, slowly pushing them into low enough orbits to be captured and burned up by our protective atmosphere. Unlike nets or tethers, a space laser could train in on multiple different targets per day, slowly lowering each one’s orbit independently until they reach the threshold altitude. Because the reaction pressure on the satellite from its own laser would be relatively small, its likely the spacecraft could be adequately controlled using minimal active propulsion. Outfitted with solar panels, a space laser would have a nearly infinite supply of ammunition to quell the rising threat of small space debris.
Of the 128 million pieces of space debris in orbit smaller than 10 cm, few of them outweigh a kilogram. To this end, let’s imagine a space laser capable of deorbiting any hunk of space garbage from low-Earth orbit (LEO) less than 1 kilogram. Most of Earth’s LEO space debris orbits within 1,600 km of the surface of our planet. From this high altitude, it only takes a change in velocity of about 322 m/s to knock a piece of debris from this relatively stable orbit, to one where it would survive in space no longer than a year. Altitudes below this require even less velocity change, so if the laser can deorbit an object as large as a kilogram from 1,600 km, then it can easily rid the rest of Earth’s LEO of small space debris.
Due to orbital mechanics, a single piece of space debris will only be in the laser’s direct line-of-sight about 8 or 9 percent of the time. While smaller debris could likely be deorbited in a single excursion, large debris must be incrementally pushed down over the course of many orbits, with long periods of waiting for the correct orbital configuration to return. A 3.7 kW laser could do the trick over the course of about 10 years. It turns out that the time to deorbit a piece of space junk is inversely proportional to the intensity of the laser, so a suped-up 37 kW laser could have the job done ten times faster. Since the laser only spends 8 or 9 percent of its time focusing on this chuck of debris, the remainder of its time could be spent deorbiting other pieces of space junk. Most small shards and bits (<1 cm, or about 1 gram), which comprise the bulk of space junk, could be deorbited in a matter of hours. Over the span of a single year, one space laser could effectively neutralize hundreds, if not thousands of dangerous orbital projectiles.
A strategic constellation of space lasers occupying a range of orbital altitudes and inclinations could be constructed and launched into orbit relatively cheaply, and with modern day technology. Multi-kilowatt precision lasers are not unheard of, and are in fact used regularly by the US military today to nullify hostile missiles and drones. Though such satellites would be fairly bulky, and require large radiator and solar panel arrays, they could still probably be designed to fold up and fit into modern launch vehicles for deployment. From a technological standpoint, the space laser has taken its place at the starting line. Sadly, it’s no coincidence that the starting gun hasn’t been fired. Since the regular operation of commercial satellite constellations has not been greatly affected, and the government has not seen a need to incentivize it, there is currently no monetary drive for anyone to clean up our orbit. Like climate change, the solution to the space junk epidemic begins with a political understanding of the issue (it also doesn’t help that high powered lasers in space are currently prohibited under international law).
Humans always seem to wait until the last minute to combat the crises which threaten our future. Still, our species has always displayed a steadfast resilience to surmounting challenges which had previously been deemed impossible to overcome. In the realm of space travel we are still taking our first baby steps into the cosmos, our feet lifting from the surface of Earth below and our eyes gazing at the vast eternity above. The immensity of space is unimaginable; it’s hard to believe that any amount of man-made objects could ever create a problem such as this. And yet, just six decades after our first endeavor into the great unknown, our efforts have put us at a crossroads. Down one path lies the complete and utter isolation of our planet from the mysteries of the universe, and the regressing of our technology back to an era before the Space Race. Down the other: space nets, space tethers, and space lasers. For the sake of the human race, we need the latter.
