NASA radar checks out ECAs, Earth-orbit crossing these, in case one is about to wipe out civilization
... Usually our planet is 
far away when the orbit crossing happens, but in 1937, 1942, 1954,... [DOC] [TLE] NASA Viz: Asteroid Crossing [PAR] Mar 5, 2013 ... A near-Earth flyby provides scientists with a rare, close-up view of an asteroid.