11 August 2017

Space Debris Cleanup

Welcome back. Toward the end of my 20 years in government, a colleague from one of the National Labs tried to challenge me with the problem of cleaning up space debris. The debris resulting from China’s anti-satellite missile test in 2007 was getting peoples’ attention.

Space Debris
To be clear, space debris was not a new concern. The Department of Defense had been tracking space objects since the Soviet Union’s first Sputnik in 1957, NASA’s Donald Kessler had warned in 1978 that the density of debris circling Earth could eventually prevent space activity in certain orbital ranges for generations, and the European Space Agency (ESA) organized the 1st European Conference on Space Debris in 1993.

Depiction of space debris in 2016. (Photo from video "Watch 60 years of space junk accumulate in 1 minute” by Stuart Grey, youtu.be/wPXCk85wMSQ)

Space debris runs the gamut of natural and artificial objects and particles. Earth-orbiting debris includes inoperable satellites, mission-related and launch equipment as well as fragments. Half a million pieces are the size of a marble or larger, and many millions of pieces are too small to be tracked. All pose a risk to space missions. (The China anti-satellite test added over 2000 pieces the size of a golf ball or larger and an estimated 150,000 particles.)

Debris-Removal Concepts
As my colleague and I ran through some of the more obvious approaches, it didn’t take long for me to learn that what would work on Earth would fail in space. Fortunately, over the years, many individuals and groups--government, industry, academia--have studied the problem in depth and offered viable concepts, as exemplified during the recent 7th European Conference on Space Debris.

For example, a consortium of European companies has developed the RemoveDebris spacecraft, which is undergoing NASA safety reviews for launch from the International Space Station, to test a net, harpoon and drag sail for deorbiting cubesats.

The Japan Aerospace Exploration Agency (JAXA) has been experimenting with electrodynamic tethers to generate magnetic drag to deorbit spent rocket stages.

ESA is planning a mission, e.Deorbit, to launch a spacecraft in 2023 that would use either a net or robotic arm with a gripper to capture and deorbit a large inoperable satellite, which may be tumbling in low Earth orbit.

And when it comes to robotic gripping devices for removing space debris, researchers from Stanford University, with support from NASA’s Jet Propulsion Lab (JPL), have made great progress with a little help from geckos.

Gecko-Inspired Adhesive and Gripper

When I was still in government, a number of investigators around the country were studying and biomimicking geckos to improve climbing robots. 
Gecko with its gripping feet.
(multiple websites)

Geckos can stick to walls and ceilings because their feet have microscopic flaps that, when in full contact with a surface, create weak, electrostatic, van der Waals forces.

The Stanford gripper uses gecko-inspired dry adhesives. Though the flaps of the gripper’s adhesive are not as extensive as those of a gecko, they function the same. They stick only if the flaps are pushed in a specific direction and need only a light push.

Adhesive patches on Stanford University’s robotic gripper for cleaning up space debris. (Photo from Stanford video www.youtube.com/watch?v=6hHv4li2JbY)

The robotic gripper has adhesives that are selectively turned on and off, a load-sharing system that scales small patches of the adhesives to large areas, and a nonlinear passive wrist that is stiff during manipulation yet compliant when overloaded. The device can gently grasp, manipulate and release flat or curved, uncooperative objects up to a meter in diameter.

With JPL’s assistance, versions of the gripper have been tested successfully in different zero gravity environments, including the International Space Station. Next step is testing outside the ISS.

Wrap Up
So, it would seem the technology to address the space debris problem is just about ready, which is none too soon given the hundreds of new satellites planned for launch. Now we face the problem of implementing the cleanup, which might be even more challenging given the costs, shared responsibilities and security concerns.

Thanks for stopping by.

Space debris--NASA review and ESA video: www.nasa.gov/mission_pages/station/news/orbital_debris.html
Kessler syndrome: en.wikipedia.org/wiki/Kessler_syndrome
China anti-satellite missile test: en.wikipedia.org/wiki/2007_Chinese_anti-satellite_missile_test
7th European Conference on Space Debris: conference.sdo.esoc.esa.int/
Clean up concepts on Space website:
RemoveDebris: spacenews.com/launch-of-space-debris-removal-experiment-delayed-due-to-safety-reviews/
JAXA electrodynamic tether: www.theguardian.com/science/2017/feb/06/japans-space-junk-mission-700-metre-tether-fails
e.Deorbit: blogs.esa.int/cleanspace/2017/01/30/e-deorbit-it-is-time-to-make-active-debris-removal-a-reality-for-the-european-space-sector/
Stanford robotic gripper report in Science Robotics journal: robotics.sciencemag.org/content/2/7/eaan4545.full
Articles on Stanford gripper on The Christian Science Monitor and ScienceDaily websites:

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