Installation 00 (Earth-2042)

"Where would someone go to activate the other rings? ...Why, the Ark, of course."

- 343 Guilty Spark to Commander Miranda Keyes

Installation 00, also known as the Ark and sometimes translated as Waypoint, is a Forerunner installation from which the entirety of the Halo Array can be activated. Installation 00 also functions as a potential safe haven from the Halo Array's strategic pulse, and as a facility to construct replacement Halos if necessary. The Ark is situated outside the galaxy, about 218 (262,144) light years from the galactic center.

Source

 * https://www.halopedia.org/Installation_00