Could the solution to eliminating dangerous space junk be a mini-fridge-sized spacecraft equipped with a big magnet, or maybe an orbiting tug that sends out a swarm of tentacles to trap a spent rocket?
If all goes well, schemes like these may be the first steps in removing the growing constellation of metallic refuse orbiting Earth. There are at least 23,000 pieces of discarded payloads, rocket bodies, and other debris greater than 10 centimeters long circling the planet, according to NASA estimates, with another 500,000 smaller objects that range between 1 and 10 centimeters. These are all moving at least 18,000 miles per hour and can stay aloft for decades before reentering Earth’s atmosphere and burning up. While in orbit, they pose a risk to commercial communications satellites, scientific and weather orbiters, and of course the International Space Station, which is currently home to seven astronauts.
In 2020, two defunct satellites missed hitting each other by a mere 40 feet about 550 miles above Pittsburgh, while a non-operational Russian satellite and an Iridium communications satellite collided in 2009 over Siberia. As a result, national space agencies and commercial firms are gearing up to sweep away space objects before something worse happens. Officials at NASA recently issued a handbook on how to avoid crashes for commercial satellite providers, and this month the agency signed an agreement with SpaceX to ensure that both prioritize safety during launches and orbital maneuvers. The agreement is a way to make sure that one party’s satellites aren’t parked over the other’s launch sites or planned spacecraft trajectories, which could lead to collisions that would generate even more debris. The Pentagon might even pay commercial firms by the ton to remove space junk, according to a recent report in SpaceNews.
On March 22, Astroscale, a Tokyo-based startup collaborating with Japan’s space agency, JAXA, launched a magnetic space trash picker-upper called the End of Life Services by Astroscale demonstration, or ELSA-d. The project consists of two spacecraft. One is a 386-pound mini-fridge-sized servicing satellite armed with a magnet. The other is a smaller, 37-pound client satellite, which is shaped like several pizza boxes stacked upon each other and has a round magnetic plate. Their first flight is a demonstration mission, designed to test how well the bigger satellite can chase and capture the smaller one, which is playing the role of a practice target. The two were attached when they launched, but once all the systems have checked out in a few months, the servicer will release the client into its own orbit. Operators on the ground will maneuver them into a rendezvous so the magnet on the bigger satellite gets close enough to attach itself to the plate on the smaller one.
If all goes well with the meet-up when both objects are moving stably, a second phase of the project will involve sending the smaller machine into a tumbling orbit, making it harder to capture. Once again, the bigger satellite will have to find and grab it using the magnet. This task is more difficult and is meant to prove to potential customers that Astroscale can successfully capture debris that is moving erratically through space. After that second capture, the two spacecraft will then enter a joint orbit and harmlessly burn up in the Earth’s atmosphere.
Future versions of the Astroscale system could be used to remove a specific company’s dead satellites, or just clear a particularly crowded patch of space that might menace a commercial or space agency’s mission. But Astroscale’s solution of using magnets to let one satellite grasp another will only work if satellite operators attach the company’s magnetic plate to future orbiters, like adding a trailer hitch for a space-bound tow truck.
“We have to make people aware that to reduce the amount of debris that exists, we have to make sure that any satellite that gets launched going forward can be removed more easily,” says the firm’s chief operating officer, former NASA official Chris Blackerby. “As more and more satellites are being launched, that risk of collisions gets higher and higher.”
So far, satellite internet provider OneWeb is the first company to agree to use the magnetic plates on its fleet of satellites—in advance of the planned October 2021 launch of its broadband service, Blackerby says.
The engineering challenges of capturing something in space are enormous. During the demonstration, Astroscale’s operators in the United Kingdom will command the main satellite through a network of 16 ground stations spread across the globe, but the smaller client satellite will be just spinning in space. Ground controllers will have to estimate the speed and direction of both objects and make sure to precisely connect the magnet and the plate, otherwise a collision could send the two tumbling into space, where they could cause trouble.
“Most of this mission hasn’t been done before,” Blackerby says. “There has been docking in space back to the Apollo days with two objects with control on both sides. But to do something on an object that doesn’t have a communication or satellite link is incredibly difficult.”
If the ELSA-d project works, the Astroscale team will begin planning a second mission to grab a defunct Japanese upper-stage rocket booster sometime in 2023, Blackerby says. Astroscale is working on other ideas to remove older space debris as well, such as by using a still-to-be-designed robotic arm, according to Blackerby.
In 2025 a European effort will attempt something similar, grabbing something moving at high speeds without being able to command it. Swiss startup ClearSpace was chosen by the European Space Agency to use a proposed tentacle-like system to reel in an 8-foot cone-shaped piece of the ESA’s Vega spacecraft booster rocket. The object was only used during launch and has been floating in orbit for several years. The plan is for the ClearSpace craft to seize the piece of the Vega launcher with its four robotic arms, then carry it back into Earth’s orbit, where the pair will disintegrate in a fiery, but quick end. (Here’s the video of how it’s supposed to work.) The ClearSpace-1 mission might be a solution for collecting pieces of space junk that are already aloft, because deploying a grappling mechanism won’t limit it to picking up satellites equipped with a magnetic plate.
ClearSpace CEO Luc Piguet says the hardest thing will be matching the speed and direction of the target, and then gripping it without bumping it and spinning it into another trajectory. “You have to determine the tumbling rate, navigate toward it, and negotiate the capture with an object that is non-cooperative,” Piguet says. “Creating more debris is something you don’t want to do.”
The task of clearing space of dangerous debris will likely increase as new commercial providers like OneWeb, SpaceX’s Starlink, AST & Science’s 5G network, and Telesat’s broadband service launch hundreds of new satellites in the coming months. Piguet says that some orbital altitudes are more crowded than others, and that the biggest traffic jam occurs over the North and South Poles, where functioning satellites intersect the paths of old pieces of space junk. “It’s at the poles where all the traffic crosses,” Piguet says. “And you have many more objects crossing each other than lower around the equator.”
While Astroscale and ClearSpace are aiming to remove debris, others are trying to develop the technology to move aging satellites out of danger. NASA and Northrup Grumann are both working on plans to service existing satellites. NASA’s servicing mission intends to cut a hole in a government-owned satellite and refill it with hydrazine fuel, according to Brent Robertson, project manager for NASA’s OSAM-1 servicing mission, which is expected to launch in 2025. Once the satellite has additional fuel, it can be controlled from the ground and maneuvered to an orbit away from troublesome debris. That will extend its useful life-span, rather than letting it end up dead in orbit.
Robertson says the lessons learned from this refueling mission will be useful down the road. “If humans are to move beyond low Earth orbit, we have to have spacecraft that are refuelable and sustainable,” Robertson says. “With this mission, we are demonstrating we can refuel a spacecraft in orbit.”
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