How do unmanned probes JUST NOT collide against any other celestial bodies?

You obviously don't understand exactly how BIG space is. There are a couple of instances of satellites in low Earth orbit colliding, but satellites are very dense at that altitude. The chances of a space probe colliding with anything is just about zero. Very few probes have been recovered, unless there was some reason to recover them. Most satellites burn up in the atmosphere of the planet they orbit. The four probes which have left the solar system are not aimed at anything, and probably will never hit anything (despite the original Star Trek movie).