That Lucky Old Sun

 is a quest in Fallout: New Vegas.

Quick walkthrough
You head to Helios One and talk to the guards outside. They direct you in to find some crazy scientist named Fantastic. He tells you that the mainframe controls need to be connected and the mirrors have to be fixed. You head out side and fix the mainframe (Watch out when you go to the objectives, there are many booby traps all around). When you go to the last terminal, there are 3 NCR guard dogs waiting inside. Ignore the dogs and use the terminal, they will not follow you out of the area.

Detailed walkthrough
When you first approach the HELIOS One station from the south, you will be approached by a female NCR officer. With either a successful speech check, or a science skill option you can convince her to allow you inside, and that you should talk to the "idiot wearing sunglasses".

Proceed to the back of the factory, following the compass. You will soon come across a door with a light above it; this leads to the NCR's de-facto science lab at the power station. The "Idiot wearing sunglasses" is a man by the name of Fantastic, who explains that he got the job by lying to NCR when they were going door to door, asking if anybody knew a scientist.

You will get the password to the other (western terminal) from him and the place you can direct the power to. Next you must speak to Ignacio Rivas in the next room. He will explain that the HELIOS One-station is not only a power plant, but also a developmental facility for a weapon known as "ARCHIMEDES", and that he has kept the NCR in the dark about the weapon, fearing what they may do with it. He will also give you the password for the eastern set of mirrors, and explain that you must go to the control computers for the mirrors, attempt to reconnect with the mainframe, then go to the mainframe to redirect the mirrors, and direct the power.

Proceed out the back door into the mirror field, and head for the control computers, which are each located in small shacks nestled among the mirrors. The shacks are guarded with traps and attack dogs, and can be dangerous, and possibly lethal to an unwary player. After you reset the mirror control computers, you must enter the tower through a door at the base and fight your way through Mark III Turrets and Protectrons till you get to the bottom of the basement, where a working elevator takes you to the mainframe.

NOTE!: You need at least 35 Repair to access the mainframe due to lack of sufficient power which requires you to use an auxiliary generator next to the mainframe.

It says here that the eastern password was from [scientist], but i found eastern password on a desk on the second floor, there is a staircase iat the end of the hallway to the right of the front desk that takes you to the second floor, then the password looks like a holotape and is sitting on top of the desk.

Time for some choices.

McCarran and Las Vegas Strip
Simply select the first option 'McCarran and Las Vegas Strip', exit the mainframe, take the stairs up and follow your compass to outside. Once outside, go down the spiral stairs and activate the Reflector Control Panel and enjoy the show. After your screen turns normal, go back to Fantastic and listen how he tells you he's going to take most of the credit. This will get you 350 XP and New California Republic reputation.

Optional: Arm ARCHIMEDES Plant Defense System
This section of the quest is entirely optional. While accessing the mainframe and after you have configured the grid, a new menu option appears. After "Arms ARCHIMEDES Plant Defense System" has been selected, you will start hearing a alarm. This can be toggled so pressing it once is not your final choice. Actually, everything can be altered as long as you haven't touched the Reflector Control Panel.

As you're making your way outside after arming ARCHIMEDES, you're probably hoping to see something in lines of Megaton explosion. After activating Reflector Control Panel and some waiting, you will see it's nothing nearly as awesome. A lot of NCR troopers will die below the Reflector Control Panel and New California Republic will start shunning you. This will negate all the rewards except the experience.

Fremont and Westside
Select Fremont and Westside as your grid configuration, go outside and activate Reflector Control Panel to enjoy the show. When you have seen enough, return to Ignacio Rivas to be congratulated on your well made choice. He will tell that hopefully NCR's curiosity in the plant has been satisfied and they won't dig any deeper. You will gain 350 XP, 3 Stimpaks, 2 Doctor's Bags and a moderate amount of [Followers of the Apocalypse]] reputation.

Full region
Select the third option, "Full region" as your grid configuration, go outside and activate Reflector Control Panel to enjoy the show. When you have seen enough, return to Ignacio Rivas to be congratulated on your very admirable choice. He will tell that hopefully NCR's curiosity in the plant has been satisfied and they won't dig any deeper. You will gain 1 Big Book of Science, 350 XP, 3 Stimpaks, 2 Doctor's Bags and A LOT OF [Followers of the Apocalypse]] reputation (this will get you to the status of Accepted if you haven't had a previous encounter with them).

Archimedes II
Select the fourth option, "Archimedes II" as your grid configuration, go outside and activate Reflector Control Panel to enjoy the show. When you have seen enough, return to Ignacio Rivas who will tell you that NCR's curiosity will be satisfied when the plant's output has improved. You will gain 350 XP, 2 Stimpaks, 1 Doctor's Bag and a moderate amount of Followers of the Apocalypse reputation.

Full region (Emergency output level)
Select the fifth option, "Full region (Emergency output level)" as your grid configuration, go outside and activate Reflector Control Panel to enjoy the show. When you have seen enough, return to Ignacio Rivas who will be disappointed of all the energy wasted, but he will be relieved as the plant can not be used as a weapon anymore. You will gain 350 XP, 3 Stimpaks, 2 Doctor's Bags and Followers of the Apocalypse reputation.

NOTE: Full Region (Emergency output level) has a glitch. When you talk to Ignacio and tell him that "I overloaded the plant. No one will be able to use it to power a weapon.", the option will stay meaning that you can get infinite Experience Points, Stimpaks, Doctor's Bags.