In this page you can find a detailed description for unlocking "Ball Lightning" achievement in Prey. You get this achievement by using an alien ability called Electrostatic Burst to knock down at least two operators (the little flying machines) at the same time.
Getting this achievement is only possible after you buy an alien ability called Electrostatic Burst, available after scanning Voltaic Phantoms and Typhon Technopaths. Next, you must go to a location where you can find at least two operators (the flying machines).
The best choice of a location for this achievement are those areas where you can find corrupted operators because when they notice you they start chasing the main character so it is easy to "position" them next to each other. The perfect place is the passage to the Crew Quarters in Arboretum which is presented in the picture 1. The first operator is in the Security Station (you must unlock it) and the second one is near the airlock that leads to the Crew Quarters. Get the attention of one of the operators so it will start chasing you. When both of them are close to each other use your ability (an example is presented in the picture 2). You can play on easy or medium difficulty level so you won't die from operators' flamethrowers while you are waiting for a perfect moment to use the ability.
Warning - In order to get this achievement you only have to knock down the operators, that is force them to make an emergency landing and crush into the ground. You don't have to completely destroy them.
You can also try to get this achievement in many other locations, e.g. atrium in the Psychotronics or the Machine Shop in the Hardware Labs. Also you should remember that you can get new operators from operator dispensers. However, the game won't allow you to summon another operator of the same type if a previous machine is still operational.