This European Space Agency simulation shows the number of spacecraft currently orbiting the Earth, with many expected to either burn up in the atmosphere, or move to a distant ‘graveyard orbit’ when they reach end of life
By the Editorial Team,
Published by Space Daily, 21 July 2026
Donald Kessler’s 1978 model warned that once orbital debris density crossed a threshold, collisions would trigger more collisions in a decades-long cascade. By July 2026, ESA estimates more than 140 million fragments circle Earth — and the threshold is already behind us.
In 1978, NASA astrophysicist Donald Kessler published a paper arguing that once the density of objects in low Earth orbit passed a certain threshold, collisions between them would generate more debris than atmospheric drag could remove — and that debris would trigger more collisions, and those collisions more debris, until entire bands of orbit became too hazardous to fly through. The model did not require a rocket war or an anti-satellite weapon. It required only arithmetic. And by every public measurement available in July 2026, the arithmetic has already tipped.
The European Space Agency now estimates more than 140 million objects smaller than 10 centimetres are circling the planet, most of them too small to track, all of them moving at roughly 7 kilometres per second — about ten times the muzzle velocity of a rifle round.
What Kessler actually predicted
Kessler’s 1978 paper did not claim a chain reaction would happen next Tuesday. It claimed something subtler and worse. Above a certain density, the rate of new debris created by random collisions would exceed the rate at which atmospheric drag pulled old debris down. The population would grow on its own, without a single new launch.
The threshold was a tipping point, not a cliff. Once crossed, the cascade would play out over decades. Satellites would fail. Replacements would launch into a dirtier sky. Each generation of hardware would face a slightly higher collision probability than the one before it. The bands most affected — roughly 700 to 1,000 kilometres up, where sun-synchronous imaging satellites live — would eventually become unusable for any spacecraft not built like a tank.
The 1978 paper assumed a satellite population in the low hundreds. As of mid-2026, active satellites number in the tens of thousands, and a single operator flies close to 10,000 of them.
Why a paint fleck matters at orbital velocity
Kinetic energy scales with the square of velocity. A fragment 5 centimetres across, moving at 7 kilometres per second, carries roughly the energy of a small car hitting a wall at highway speed. A fleck of paint can crack a shuttle window. A bolt can end a mission.
Eric Felt, a retired U.S. Space Force colonel now at the University of Texas, has explained that small objects traveling at orbital velocities can cause catastrophic damage to satellites. His team is working with the Florida startup SOAR — whose advisor is Donald Kessler himself — on a passive shielding satellite designed to absorb sub-10-centimetre debris that ground radars cannot see. That partnership was announced on 15 July 2026.
The tracked catalogue — objects large enough for the U.S. Space Surveillance Network to see and follow — contains something like 40,000 items. The untracked population is roughly 3,500 times larger.
The threshold, and the year it was crossed
Different research groups place the tipping point in slightly different places, but all of them are now behind us. Analysts have argued since the mid-2000s that the 900-to-1,000-kilometre altitude band was already unstable — meaning collisions there would generate more debris than drag removed even if launches stopped tomorrow.
Two events sharpened the picture. In 2007, China destroyed its own Fengyun-1C weather satellite with a ground-launched missile, creating more than 3,000 trackable fragments in a single afternoon. In 2009, the defunct Russian Kosmos 2251 satellite collided with the active Iridium 33, generating roughly 2,000 more. Those two events alone increased the trackable debris population in low Earth orbit by about a third.
Every fragment is now its own potential bullet, orbiting for decades before drag brings it down. And the fragments from a collision at 800 kilometres will circle the planet for a century or more.
See: Original Article
