Depends on the tracking mechanisms employed. For example, using radar, the object you're tracking must be larger than the wavelength of the radar being used.

Depends on the tracking mechanisms employed. For example, using radar, the object you're tracking must be larger than the wavelength of the radar being used. Also note there is a difference between focused "tracking" and "searching". Radar also suffers from atmospheric attenuation, so there's a tradeoff between frequency, power, wavelength, etc. I don't know what systems they're using to track LEO objects, but it's certainly within the realm of reasonable. A decent primer: http://faculty.nps.edu/jenn/Seminars/RadarFundamentals.pdf http://faculty.nps.edu/jenn/Seminars/RadarFundamentals.pdf