In the late 1970s, when the space race between the United States and the USSR was thriving and more and more satellites were being sent into orbit, scientist Don Kessler sounded a warning.
The amount of space junk could become so great that collisions would become inevitable, he predicted. A chain reaction would be created, causing even more collisions, making it impossible to navigate any spacecraft or equipment.
He estimated it would take three or four decades to become a reality.
At that point it was dreams of people routinely flying into outer space that experts envisaged were under threat.
However, space defence experts are now expressing concerns over the possibility of rogue states or groups causing worldwide chaos by using such a scenario to bring down hundreds of satellites.
It was raised during questioning of leading space scientists by a UK parliamentary committee hearing on space defence.
A terrorist group or hostile state could hack into satellites, forcing collisions between objects that could cause a cascade in which hundreds collide, members were told. This would put global technology back 70 years with GPS, communications and many other benefits provided by satellites rendered useless.
Space experts were asked by Tobias Ellwood, the defence committee chairman, about “non-state actors enjoying the idea of triggering the Kessler Effect”, in which satellites tumble through space “causing a mesh around our world taking us back to the 1950s”.
“How concerned are you about the Kessler Effect actually being triggered?” he said.
“The issue of space debris and space sustainability is of concern not just to defence in the military but more broadly and therefore it's something we should be deeply concerned about,” said Dr Mark Presley, a space strategy expert. He said that this included “nefarious activity” by “non-state actors”.
What is the Kessler Effect?
The Kessler Effect, also known as Kessler syndrome or collisional cascading, was proposed by Nasa scientist Donald J. Kessler in 1978. His theory was that the density of space objects over time would become so great that collisions between space objects would cause a domino effect, with each collision generating even more space debris and making collisions more likely. If sufficient collisions occurred, satellites would be rendered useless.
There are an estimated 2,666 satellites orbiting the Earth, with thousands more tiny bits of debris that could trigger a catastrophic collision.
At present, one satellite a year is destroyed in collisions with space junk, with a one-kilogram piece of debris having the mass to destroy a spacecraft. In Kessler's theory the fragments from this could then hit other satellites with the resulting cascade of disintegration causing massive destruction.
The Kessler Effect has been widely discussed in fiction, with Russia creating a debris field when it shoots down an old satellite in the film Gravity. Similarly, in a Tom Clancy franchise novel Oath of Office, Iranian dissidents attempt to trigger the Kessler Effect by firing two Russian nuclear missiles at a satellite.
Dr Presley, a lead adviser at the space consultancy Map Analytica, said threats came in “kinetic and non-kinetic” forms, with the former mainly from anti-satellite missiles or direct-energy weapons and the latter from hackers able to break into guidance systems.
“What's interesting to look at is what we call the non-kinetic threats to space things, like jamming, dazzling or spoofing or cyber-attack,” said Dr Mark Hilborne, a defence studies lecturer at Kings College London.
MPs also heard that China and Russia had developed interceptors that could successfully destroy a satellite.
While space weapons made sense during the Cold War, countries such as China and Russia were now highly reliant on satellites, he said. “Any intercept would create the risk of fratricide and so I think states like China, the more they rely on space, the less likely they are to conduct those kinds of attacks in space.”
But Dr Hilborne suggested that countries using state-level cyber-attacks, such as Iran, China and Russia, would have the technology to attempt similar operations in space with a degree of “plausible deniability”.
In 2017 Russia was found to have manipulated GPS navigation systems for shipping in the Black Sea. To deter against spoofing, in which accurate information is replaced with false data, greater resilience was needed in the space infrastructure, the experts said.
More space operations centres, such as the RAF’s Space Command, were needed to identify “nefarious activity in space”, allowing countries such as Britain “to take action early on to counter any threats, whether it be state based or non-state based” Dr Presley said.
With the potentially catastrophic fall-out from events such as the Kessler Effect, it is vital for an international agreement to establish the “norms of behaviour in space for the benefit of everybody” he said.
Rather than a large United Nations treaty, that would take years to thrash out, a form of common regulations and licensing might be quicker and more effective.
“This will mean a more secure space environment rather than an international treaty, which would be preferable, but I think the pragmatic realisation is that could take many, many years,” Dr Presley said.