Intentional collisions of objects in outer space (ASAT) imply a military activity which results in the destruction of the targeted object in orbit by colliding with it. ASAT were performed by top spacefaring nations, the United States (U.S.), China, India and Russia, by using direct-ascent intercontinental ballistic missiles against their own satellites located in Low Earth Orbit (LEO). Examples from recent years include the ASAT performed by China in 2007 at an altitude of about 863 km, India in 2019 at an altitude of about 283 km and Russia in 2021 at an altitude of about 480 km. 

Two major consequences result from ASAT. The immediate outcome is the deliberate creation of space debris, the collision in orbit generating thousands of pieces of trackable debris which start floating in space in an uncontrolled manner. The space debris could further increase in number because of the cascading effect and could even spread in higher orbits, therefore posing important threats to the safety of space operations in different orbits. Another consequence of ASAT is the threat to security in outer space. Thus, the ASAT can harmfully interfere with the operations of space objects pertaining to other countries, or even limiting the other countries options to accessing and using space.

An assessment of the legality of ASAT implies a comparison between hard law and soft law provisions. The UN Space Treaties, including the Outer Space Treaty (OST), do not contain specific provisions regarding ASAT, whether this is allowed or prohibited. However, because ASAT negatively impacts the space environment and the operations of other actors in orbit, it could be considered a violation of the principles stipulated in Article IX OST. Moreover, the UN Space Debris Mitigation Guidelines have clear provisions against the creation of space debris, which is one of the consequences of ASAT. Therefore, even if these guidelines are voluntary in nature, there is a political and diplomatic consensus that States should avoid the creation of space debris. This is one of the reasons behind the implementation of these guidelines at national level, and imposing obligations to private companies to limit the creation of space debris. 

Overall, the concern at international level for reducing space threats, including ASAT, reiterates the relevance of negotiations on norms of behaviour in outer space. Among the most significant initiatives at international level regarding sustainability of outer space, it could be identified the UNCOPUOS Guidelines on the Long-term Sustainability of Outer Space Activities, the UNGA First Committee Resolution on norms of behaviour and the ongoing push for an international Space Traffic Management (STM).