From Halopedia, the Halo wiki
Skyhooks are payload-transportation structures anchored to a planetary orbit. Earth and its natural satellite, Luna, house a number of military-oriented skyhook defense complexes in their orbits. Crucial to the defense of humanity's homeworld, these stations came under attack by the Covenant during the Battle of Earth in late 2552. ONI security personnel equipped with Air Assault-class armor were deployed to prevent the Covenant from gaining control of these facilities. The Orbital armor variant also underwent extensive field-testing in these engagements. The colony world of Vodin also housed a number of skyhooks, which were attacked by the Covenant when they invaded the planet in 2532. During the battle, Randall-037 fell into Vodin's atmosphere from one of these platforms, landing in one of the planet's oceans.
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