While the odds of navigating an asteroid field are not as bad as 3,720 to one—as C-3PO famously told Han Solo in The Empire Strikes Back—space debris is a growing problem in low Earth orbit with millions of pieces of spacecraft, flecks of paint, jettisoned engineers, decommissioned satellites and more flying around at 18,000 miles per hour.
There are no international space laws to clean up debris, but Europe, the United States, China and other countries have committed to working together to ensure the problem doesn’t get worse.
This month, for example, the European Space Agency (ESA) announced ClearSpace-1, Europe’s first space mission to remove an inactive ESA-owned object from low-Earth orbit. ClearSpace, a spin-off company established by an experienced team of space debris researchers based at Ecole Polytechnique Fédérale de Lausanne, won the service contract following a competitive process.
The ClearSpace-1 mission, scheduled for 2025, will target the Vespa (Vega Secondary Payload Adapter) upper stage left in an approximately 800 x 660 km altitude orbit. The ClearSpace-1 ‘chaser’ will be launched into a lower 500-km orbit for commissioning and critical tests before being raised to the target orbit for rendezvous and capture using a quartet of robotic arms. The combined chaser plus Vespa will then be deorbited to burn up in the atmosphere.
At a mass of 100 kg, the Vespa is close in size to a small satellite with a simple shape and sturdy construction, making it a suitable first goal. The ESA intends to progress to larger, more challenging captures, including multiple objects at one.
“NASA and ESA studies show that the only way to stabilize the orbital environment is to actively remove large debris items,” said Luisa Innocenti, director of ESA’s Clean Space Initiative. “Accordingly, we will be continuing our development of essential guidance, navigation and control technologies and rendezvous and capture methods through a new project called Active Debris Removal/ In-Orbit Servicing—ADRIOS. The results will be applied to ClearSpace-1. This new mission, implemented by an ESA project team, will allow us to demonstrate these technologies, achieving a world first in the process.”
In June 2018, astronauts at the International Space Station (ISS) deployed the RemoveDEBRIS spacecraft to test the efficacy of several key Active Debris Removal (ADR) technologies on mock targets in low Earth orbit. The spacecraft, operated by the University of Surrey’s (UK) Space Centre, comprised a net, a harpoon, a drag sail, and two CubeSats. In the months following deployment, the net was successfully deployed, a test of the onboard vision-based navigation system produced positive images, the harpoon penetrated a simulated target about 5 feet away, but the deployment of the drag sail failed.
New research
Now, in research recently published in the Journal of Laser Applications, Chinese researchers have developed human brain-inspired algorithms for laser ranging telescopes that can significantly improve the success rate of space debris detection.
Tianming Ma and colleagues from the Chinese Academy of Surveying and Mapping and Liaoning Technical University trained a neural network—algorithms modeled after the human brain’s sensory inputs, processing and output levels—to recognize space debris using two correcting algorithms. The Genetic Algorithm and Levenberg-Marquardt optimized the neural network's thresholds for recognition of space debris, ensuring the network wasn't too sensitive and could be trained on localized areas of space. The team demonstrated the improved accuracy by testing against three traditional methods at the Beijing Fangshen laser range telescope station.
The observation data of 95 stars was used to solve the algorithm coefficients from each method, and the accuracy of detecting 22 other stars was assessed. The new pointing correction algorithms proved the most accurate, as well as easy to operate with good real-time performance.
Ma said he will continue to refine the method to “provide effective help for the safe operation of spacecraft in orbit.”
“Imagine how dangerous sailing the high seas would be if all the ships ever lost in history were still drifting on top of the water,” said ESA Director General Jan Wörner. “That is the current situation in orbit, and it cannot be allowed to continue.”
Photo courtesy of NASA