High above ground, faceless machines are flying overhead with the ability to drop hundred pound explosives on unsuspecting targets. This isn't a scene from the next Terminator movie; it is a regular occurrence in countries like Afghanistan, Yemen, and Pakistan where the US military is laying rubble to suspected terrorist hideouts.

It is no surprise that there is a groundswell of criticism around the world to the practice of sending unmanned military drones to assassinate people which has even included an American citizen last fall. While the United States is the only country where more people approve of drone strikes than disapprove according to a 2012 Pew global survey, the issue may be coming closer to home very soon.

Earlier this year, Congress approved the use of unmanned drones in US airspace and some experts estimate there could be 30,000 drones in US airspace by 2020. See the infographic below to learn some interesting facts that you should know about military drones.