How do you discover vault 87?

You have to get close to the area, then use both Rad Away and Rad-x, along with a decent rad resistance suit or armor, then just make a run for the middle of it. Hotkey the rad away, and pop it as you go. It may take a few tries...but it can be done. Another suggestion will be getting the Cyborg perk which will allow to not only take 1/2 of the damage you normally would but resist rads. So take advantage of the perks that have RAD RESISSTANCE.