NERC's Space Geodesy Facility, hidden away in the English countryside, fires lasers at satellites. Because it turns out that knowing a satellite's position exactly is really, really difficult. More about the Facility: http://sgf.rgo.ac.uk/ Thanks to Jay Dickieson for the suggestion! I'm at https://tomscott.com on Twitter at https://twitter.com/tomscott on Facebook at https://facebook.com/tomscott and on Instagram as tomscottgo