NASA radar checks out ECAs, Earth-orbit crossing these, in case one is about to wipe out civilization
...... Radar observations are one of the few ground-based techniques that reveal... [DOC] [TLE] The Threat of Near-Earth Asteroids - U.S. House of Representatives [PAR] While many of these pose no threat of collision with the Earth, a subset known as 
''Earth-crossing asteroids'' (ECAs) and ''potentially hazardous asteroids'' (PHAs) 
have ...