Outer Space Institute – International Open Letter on Kinetic Anti-Satellite (ASAT) Testing

2 September 2021

The Outer Space Institute is pleased to publish the International Open Letter on Kinetic Anti-Satellite (ASAT) Testing, which urges the UN General Assembly to take up consideration of a treaty that would prohibit conducting debris-generating anti-satellite weapon tests. The letter with an appended list of early signatories is available HERE.

The Outer Space Institute is a transdisciplinary international institute dedicated to space studies.


The number of active and defunct satellites in orbit has grown from 3300 to over 7600 in the last decade, with the potential addition of as many as 100,000 active satellites within the next ten years. This rapid growth is raising concerns about collisions and the proliferation of space debris, endangering all forms of space use, from crewed missions, to communications, to Earth observations and environmental monitoring, to space-based astronomy. New practices are needed for the safe and sustainable use of space.

A major step toward this end would be a kinetic ASAT test ban treaty. Kinetic ASAT weapons, whether ground-based or space-based, employ high velocity physical strikes through the use of a ‘kill vehicle’ or shrapnel to destroy or disable objects in orbit. Due to the high impact energies involved, debris from a kinetic ASAT test often ends up on highly eccentric orbits that cross multiple satellite ‘orbital shells’ twice per revolution. If just one piece of debris from such a test collides with a satellite and causes a major fragmentation event, this could lead to additional events affecting all States, which could include further fragmentations, satellite failures, or service disruptions.

A kinetic ASAT test ban treaty would prohibit the use of any high velocity physical strikes during testing. ‘Fly by’ tests would still be permitted.

Even low-altitude kinetic ASAT tests that seek to minimize long-lived debris are problematic because the high impact energies are still able to place some of the debris on eccentric orbits that can extend more than 1000 km above the test altitude.


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