Space

Researchers Are Turning to Game Theory to Tackle Space Debris

Removing space debris is important for securing safe satellite missions.

Emiko Jozuka

Emiko Jozuka

Space debris floats around Earth. Image: European Space Agency

Rogue pieces of space debris present a massive threat to present and future space activity. And as well as being a logistical problem, it can also get political.

According to Karl Tuyls, a professor of computer science at the University of Liverpool, there are currently more than 23,000 space debris objects larger than 5-10cm in Earth orbit. These 10cm diameter objects, he said, can even cause spacecrafts to disintegrate upon impact. What's scarier is that an influx of space debris can eventually result in what's know as the Kessler syndrome—a catastrophic cascade of collisions.

So what's the best method of eliminating hazardous space trash?

Tuyls is part of a team of researchers from the University of Liverpool who reckon they can use game theory to help analyze its accumulation as well as assess more effective ways of dealing with it.

For the uninitiated, game theory is used to study the mathematical models of cooperation and conflict between different groups of decision-makers. These groups can be everything from individuals, organizations, governments to intelligent or automated computer programs—or space debris removal.

"What we hope is that we can introduce a realistic mathematical model of the space debris situation, i.e. a debris removal game that can be used to perform a game theoretical or strategic analysis, including the computation of equilibrium strategies that can potentially clarify different sorts of behaviour of entities involved in space debris accumulation," explained Tuyls in an email.

Teaming up with the European Space Agency, these computer scientists from the University of Liverpool want to introduce a 'debris removal game' to the strategies of clearing up space trash. This essentially models real world space debris accumulation and the decision making processes of space agencies and other parties, such as governments, who are involved in the cleaning up of space debris. Their data is based on computer simulations and data stores in space debris databases.

Rocket body explosions can become space debris. Image: European Space Agency

The researchers hope that their modelling will provide both an understanding of why some parties want to get involved in clearing space debris and why others don't. Tuyls explained that the current problem is that either one party takes action at a huge expense, or waits for others to do "the dirty work" first.

"The risk of the latter action is that if everyone waits, the joint outcome will be catastrophic, leading to what in game theory is referred to as the 'tragedy of the commons,'" said Tuyls. "This refers to a situation in which the involved decision-making entities act solely according to their individual self-interest, instead of taking group interests into account."

Since both space and commercial agencies are looking to launch more satellites into space in the future, making sure that space debris is under control is crucial.

"An active debris removal mission will have a positive effect for all satellites in the same orbital band. This leads to a dilemma for the involved parties (or space organizations): they are faced with the decision between acting now or postponing to take action," said Tuyls.

Over the years, researchers have come up with several hypothetical methods to clear space debris. Proposals have included everything from snagging it with robotic arms and harpoons, using the power of electricity to slow down its movement, and deploying the drag of a solar sail to push orbiting space debris into lower orbits.

Aside from potentially tackling space debris, game theory has also been used to solve other real world problems.

"Game theory has been successfully used in the past to model for instance conflict situations in politics, arms races such as the cold war that can be modelled as a game, in which the nation has the choice to either arm or disarm (in which disarming involves a high risk of the other party continuing to arm)," said Tuyls.