Afaik I know there is a radar for observing space debris in Germany though I don't know whether it can scan the whole Earth surroundings or just a segment.
With respect to asteroids, we discover them through optical telescopes, right?
Now I've come across the USS Nimitz accident, where there might be something visible on radar but not visually.
Would such objects move around Earth orbit, what are our capabilities to discover them and what are current limitations?