As plans proliferate to launch thousands of new satellites into low Earth orbit (LEO) for daily Earth-observation updates and broadband data links, so do the clouds of hypersonic debris that threaten to form an impenetrable barrier to future space operations.
To mitigate the danger to the growing off-planet economic infrastructure, engineers on three continents are working on different concepts to clean up the orbital pathways. The problem is similar to halting the growth of  carbon and other greenhouse gases injected into the atmosphere by human activity—it can be mitigated at the source or after the hazard is created.
For space debris, the former approach is already underway. Now at least three different approaches for removing debris are under study—direct capture and deorbit of large pieces of debris; slowing debris to deorbit speeds by interacting with Earth’s geomagnetic field, and sweeping valuable satellite orbits of small bits of dangerous debris with impact platforms the size of football fields.
The European Space Agency (ESA) says its E.Deorbit demonstration spacecraft will conduct the first active debris-removal mission as early as 2023. Its goal is to capture a heavy, ESA-owned piece of debris and remove it from an altitude of 800-1,000 km (500-620 mi.) in a near-polar orbit, returning it to burn up in the atmosphere.
The Japan Aerospace Exploration Agency (JAXA) is testing the use of a tether as an electron-emitting cathode to interact with the geomagnetic field and thus reduce the spacecraft’s speed, eventually causing a destructive atmospheric reentry.
In the U.S., Launchspace Technologies has applied to patent a concept that would position huge structures in orbits where debris too small to track would collect in them over time, clearing the orbital space like a window screen on a buggy night for upcoming smallsat constellations to operate more safely. The company sees commercial potential in its idea, with satellite operators and governments paying for the debris-clearing service.
Orbiting space-debris platform
Orbiting platforms as large as football fields could sweep high-value orbits of debris too small to track. Credit: Launchspace Technologies Corp.

Time is of the essence. Debris from a staggering number of various spacecraft, inactive satellites and rocket upper stages pose a collision threat to operational satellites. Currently, the U.S. Space Command’s Joint Space Operations Center tracks more than 22,000 objects orbiting Earth, a mere 5% of them functioning spacecraft. The relevant diameter changes depending on the orbit. In geostationary orbit, a satellite may be knocked down by a 20-cm (8-in.) object. In LEO, much higher relative speeds make 1-cm debris—usually too small to track—just as dangerous.
The International Space Station (ISS) is shielded to withstand an impact by debris up to 1 cm in diameter. Thanks to monitoring from the ground, engineers can modify the outpost’s orbit to avoid a collision with larger objects, and  they do so 4-5 times a year. But the risk is increasing. Even if all space launches were halted tomorrow, the amount of debris would continue increasing, mainly driven by collisions and explosions in low orbits.
The Interagency Space Debris Coordination Committee has set international guidelines on what to do when a satellite reaches the end of its life, such as depressurizing tanks. However, these are best practices—not a binding agreement—and not every satellite operator and manufacturer follows them.
JAXA tested its electrodynamic tether concept earlier this month with an experiment in orbit that it says was a partial success. A 700-m-long (2,300-ft.) conducting cable with a 22-kg (44-lb.) mass on the end failed to deploy as planned from the Kounotori H-II Transfer Vehicle (HTV-6). Nonetheless, JAXA controllers were able to use the HTV itself to test the system’s electron-emission hardware, according to a JAXA spokesman. The experiment was conducted after the vehicle separated from the ISS at the end of its mission.
E.Deorbit spacecraft
The E.Deorbit spacecraft could clamp a defunct satellite and then send it into the atmosphere to burn up. Credit: David Ducros/ESA

By using a tether as an electron-emitting cathode to interact with the geomagnetic field, JAXA believes it can slow a spacecraft enough to deorbit it. Tethers could be part of a satellite’s design or be attached by a space tug, according to the agency.
Also targeting large debris, Europe’s E.Deorbit is being developed to process images from sensors such as lidar, a multispectral camera and a visual camera to understand the dynamic and kinematic properties of the object. Its sophisticated guidance, navigation and control system aims to ensure “a safe and controlled synchronized approach.”
ESA engineers are studying two capture techniques. A robotic arm fitted with a gripper could capture an appendage on a spacecraft, or a net could be deployed and wrapped around the debris. Once the debris is hooked or netted, E.Deorbit would use its thrusters to move it down to atmospheric destruction.
The first mission could take place in 2023. E.Deorbit would be launched from Kourou, French Guiana, on a Vega C rocket. Target inspection would follow, with rendezvous and capture of the target debris after that. Reentry would take place in April.
ESA’s 2016 Ministerial Council allocated €41 million ($43 million) for a “maturation phase” consisting of detailed system design and development of “key technology building blocks” in navigation and robotics. ESA aims to present E.Deorbit to the next ministerial council, in 2019, for a decision on implementation.
JAXA deorbiting technology
JAXA tested electromagnetic deorbiting technology with the HTV-6 vehicle itself after a 700-m tether failed to deploy. Credit: NASA

As with the Japanese concept, space tugs may be necessary to deploy the debris-capture structures conceived by Launchspace Technologies, an engineering and professional education consultancy in business since 1970. To let the debris come to the collector, instead of sending devices to collect debris, the company has identified specific orbits that it says would be good places to position “impact devices” designed to snag debris at the small end of the scale—below 5 cm—and either capture it or slow it down to lower its orbit.
“There is an orbital situation in which we can do everything in one single plane,” says Marshall Kaplan, the company’s chief technology officer. “This does not require a plane change, so that makes it extremely easy to maneuver. Our power requirements are extremely small compared to the other approaches.”
Kaplan says his proposed spacecraft would maneuver to avoid active spacecraft and large pieces of debris, while using Whipple shields and advanced materials to catch smaller pieces of debris moving at hypersonic velocities. The orbital sites are part of the patent application, which Kaplan says involves the debris-removal architecture rather than specific hardware approaches.
Launchspace is in talks with several companies that could develop and manufacture the spacecraft, says Kaplan, who is scheduled to present his concept March 9 at the Satellite 2017 conference in Washington. It would be a private development that governments could join as customers, along with commercial satellite operators.
In addition to the “satellite constellation protection service,” the system operators would market the platforms themselves for hosted payloads supplied by commercial and government customers. Kaplan says the final system would require “several” platforms in different orbital locations.
Total cost would be in the billions of dollars, but more definition work is needed to establish exactly how many of the big platforms would be needed, and how they would be assembled. Long-range possibilities include in-space manufacture as well as assembly, he says. Regardless of the cost, debris mitigation will be necessary fairly soon, Kaplan adds, arguing that his company’s approach will be more cost-effective than others under study.
Earth orbit contained natural debris before the beginning of the Space Age. The ISS and other spacecraft are shielded against micrometeoroids as well as manmade debris. Kaplan says that while he believes “there is no other reasonable way” than his company’s concept to mitigate the problem, even a full-up debris-capture system will not be perfect and does not need to be.
“There is a high-density [debris] zone at about 800 km, for example,” he says. “So we are going to focus on those areas where the density is especially high for the small debris. We are shooting for, just nominally over a 10-year period, to reduce the debris by about 20%.”