Fallout NV: HELIOS One

Here is a screenshot of HELIOS One.

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HELIOS One is a Poseidon Energy solar plant that generates and provides power to the New Vegas Strip, Freeside, and other settlements in the Mojave Wasteland. It also contains the control system for two satellite weapon platforms, Archimedes I and Archimedes II. Which are Death Rays. (But the New California Republic doesn't know about the two satellite weapon. They think is just a power plant.)
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After the Enclave was defeated in Fallout 2 in years of 2241, the NCR and the Brotherhood of Steel had uneasy alliance. But in the year of 2253 the NCR and the BoS went to war with each other. And even though the BoS had superior technology, the NCR had more Soldiers and that they won the war. (The NCR-Brotherhood War was part of the Van Buren project. This part is canon.)

In 2274, the NCR set its sights on the Mojave chapter of the Brotherhood of Steel, led by Elder Elijah, and sought control of their main base, HELIOS One. In 2276, the NCR led by Colonel Moore attacked HELIOS One and Elijah ordered his troops to protect the facility. After a lengthy battle and inflicting tremendous losses on the advancing NCR forces, the Brotherhood retreated to Hidden Valley after losing around half their chapter, and have since remained in exile. (The BoS was outnumbered 20 to 1.)

And Elder Elijah went missing, and Nolan McNamara later became the new Elder of the Mojave chapter of the Brotherhood of Steel.
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Fallout New Vegas: Ultimate Edition © Bethesda Softworks and Obsidian Entertainment
Screenshot taken from Fallout New Vegas on XBOX ONE thanks to the backwards compatibility.