Space Debris From Every Angle

Near-Earth space is an orbiting junkyard of space debris. Everything from old rocket parts and pieces of dead satellites to cameras and tools floats in orbit. None of it serves a useful function any longer, but it does threaten other spacecraft. In fact, some missions have been damaged by this orbital debris and the problem will get worse as we launch more missions to space.

So, it makes sense to remove the existing space junk, but how to do that? A company in Japan called Astroscale is working with the Japan Aerospace Agency (JAXA) to figure that out.

On July 15 and 16th, Astroscale maneuvered a demonstration satellite called ADRAS-J into place around its target. Its goal was to do a “Fly-around observation” of a rocket upper stage that launched the Greenhouse Gases Observing Satellite (GOSAT) in 2009. ADRAS-J was launched earlier this year on a trajectory to chase down space debris. The early July portion of the mission saw ADRAS-J fly around the object and get high-quality images of the object. In addition, it took data about the rocket motor’s motion in space (including its orbital parameters) and assessed its condition. The effort was successful and the teams captured great images of the motor from every angle.

The maneuvers ADRAS-J made are technically challenging, requiring fine guidance control of the ADRAS-J module. Luckily, the target object was fairly easy to approach and move around. In on-orbit maneuvers like this one, it’s important to control the relative position and attitude of the servicer unit (ADRAS-J). Such control allows it to move around the object and zero in on specific parts for further work. The rocket motor was fairly stable. However, not all bits of space junk are as stable as the rocket motor targeted for this experiment.

Challenges to Working with Space Debris

Given the huge collection of space junk out there, not everything is going to be easy to capture. Future “clean-up efforts” could involve so-called “non-cooperative targets” whose motions are more chaotic, or are dangerous to approach. Those could be very challenging. So, it’s important to have the detailed shape and surface reflectance of the real target object. For most pieces of space junk that information isn’t readily available.

For example, it’s also useful to know the changing visibility of the target object, and the influence of earth-reflected light, which disturbs the navigation sensor (the so-called Earth background problem in non-cooperative relative navigation). These add to the complexity of the mission. That’s because the servicer spacecraft must overcome those challenges for relative navigation while achieving highly accurate relative six-degree-of-freedom control around the target.

The ADRAS-J mission is part of the “Commercial Remove of Debris Demonstration” initiative from JAXA to acquire and test debris removal in space. If it’s successful, that should help clear up space for future missions leaving Earth. Astroscale Japan, Inc. will continue to operate ADRAS-J and will carry out “Astroscale missions” to further test the hardware and maneuvering capabilities.

The next step will be to perform a “Mission termination service”. That involves the transfer of a target piece of space junk to a safe orbit. This will be done in cooperation with JAXA, which has already provided extensive technical advice, testing facilities, and other activities supporting ADRAS-J’s development and operation.

Why Clean Up Space Junk?

Tens of thousands of artificial objects orbit above Earth. That includes more than 5,000 operating satellites, plus space stations, and Starlinks, and other stuff shot into orbit since the late 1950s. Eventually, as the old adage says, “what goes up must come down.” In fact, some of it does come back to Earth, which also poses a safety issue.

In the case of dead rocket motors and other nonworking pieces of space junk, not only will they come down to Earth, but they get in the way of spacecraft launches. That includes crewed launches carrying astronauts to the space stations, the Moon, and beyond.

The danger isn’t just that a collision will hurt somebody in space or on the ground. Tiny pieces of space junk can knock holes in solar panels and instruments. Bits of dust and paint flecks and other materials literally “sandblast” spacecraft on the way up. Space shuttles showed a lot of this damage. All this space debris began littering our spaceways starting with the first launches in the late 1950s. The materials are tracked by the North American Aerospace Defense Command (NORAD), and their catalogs include details of all the objects including satellites, weapons, fairings, upper stages, cameras, tools, and other pieces of debris from satellites destroyed by collisions and other actions.

It makes sense to clean up the junk that doesn’t fall back to Earth (and hopefully burn up in the atmosphere). That’s why JAXA and other agencies are looking at proactive ways to approach, apprehend, and safely store the debris (or deorbit it to vaporize, if possible). The first steps with ADRAS-J are proofs of concept that should lead to a larger clean-up job and a safer near-Earth environment for future missions.

For More Information

CRD2 Phase I / ADRAS-J Update: Fly-Around Observation Images of Space Debris Released
ESA: about Space Debris