K7-49
From Halopedia, the Halo wiki
K7-49 was the designation of an asteroid that was the site of a massive Covenant shipyard. It was located only seventeen light years from the border of the UNSC; less than an hour of travel via Slipspace. It was discovered by the prowler Razor's Edge. It had a system of artificial volcanic activity created by several high-output plasma reactors.
In 2537, Operation: PROMETHEUS took place on K7-49. The Spartan-III Alpha Company disabled K7-49, but all 300 of the Spartans were killed in the process. K7-49 was then abandoned.