Rocket's Red Glare is a challenge and achievement/trophy for the Fallout: New Vegas add-on Lonesome Road. To obtain this achievement/trophy, the Courier must possess at least one of each of the mods for the Red Glare.
This achievement may be earned at the beginning of the expansion, after ED-E opens the first commissary. Simply purchase the three upgrades, as they don't need to be installed on the gun to earn the achievement. You need at least 30,000 caps to do this. To get this achievement "free-of-cost", save before buying all the mods then reload.
Otherwise, you can find the modifications very rarely around the Divide.
Behind the scenes
The name of the achievement/trophy is a reference to the poem "Defence of Fort McHenry" by Francis Scott Key. This poem is best known as the source of the lyrics for "The Star Spangled Banner" - the national anthem of the United States.