So, this is fun. There are now so many satellites and so much space junk moving so fast ( 14.7 kilometers [9.1 miles] per second) in Low Earth Orbit that there is now ~ 1 in 10 chance of two uncontrolled satellites (one NASA, one a European agency) hitting each other.
Over 100 million bits of junk surround Earth, from abandoned satellites, spacecraft that broke apart, and other missions. Each piece of that debris, no matter how small, travels at speeds high enough to inflict catastrophic damage to vital equipment. A single hit could be deadly to astronauts on a spacecraft.
Each collision that occurs makes the problem worse, since it fragments satellites or debris into smaller pieces.