  Can a satellite dodge a collision with untracked orbiting debris? Can a
satellite dodge collision with a tracked object, making only the avoidance
man{\oe}uvers actually required to avoid collision, despite the uncertainties
of predicted conjunctions? Satellite-borne radar may distinguish actual
collision threats from the much greater number of near misses because an object
on a collision course has constant bearing, which may be determined by
interferometric detection of the radar return. A large constellation of such
radars may enable the determination of the ephemerides of all cm-sized debris
in LEO.
