Except for the highly manueverable and stealth (no emission) ones.

However, a huge amount of mass (for dropping) invalidates the former of those.

Due to limits imposed by basic physics there's no way to build a really stealthy satellite. The power source, whether solar or nuclear, necessarily generates a large radar and/or IR signature that can't possibly be hidden from military grade ground sensors.

http://www.projectrho.com/public_html/rocket/spacewardetect....

Why do you need to be powered, if you're above atmospheric drag?

Just sit up there with a receiver, bank of charged batteries, and just enough awake to monitor for wake transmissions.

Thus it will be the end of space exploration for decades (or centuries) due to the Kessler syndrome.