Radio only works for relatively close asteroids. https://en.wikipedia.org/wiki/Sentinel_Space_Telescope https://en.wikipedia.org/wiki/Sentinel_Space_Telescope

Radio only works for relatively close asteroids. https://en.wikipedia.org/wiki/Sentinel_Space_Telescope https://en.wikipedia.org/wiki/Sentinel_Space_Telescope Which was sadly cancelled: http://www.dailymail.co.uk/sciencetech/article-3255059/Nasa-pulls-plug-killer-asteroid-hunter-Sentinel-mission-set-search-dangerous-space-rocks-loses-30-million-support.html http://www.dailymail.co.uk/sciencetech/article-3255059/Nasa-... But the principle was based off infrared: http://aviationweek.com/space/ball-aerospace-ramps-sentinel-asteroid-mission http://aviationweek.com/space/ball-aerospace-ramps-sentinel-... The canadian satellite also uses light: https://en.wikipedia.org/wiki/Near_Earth_Object_Surveillance_Satellite https://en.wikipedia.org/wiki/Near_Earth_Object_Surveillance... Visible light is only one fraction of the spectrum, infrared is far more valuable for detection. Most asteroids are detected via passive observation. Radio waves are not conducive to detecting asteroids.