How NASA's Raven Module Is Developing Machine Learning Algorithms for Autonomous Spacecraft Docking

How do satellites get the maintenance they need to keep functioning? This is something of a trick question because many of them simply don't. Many satellites were put into orbit with the understanding that they wouldn't be retrieved, possibly ever. When they run out of fuel, they effectively become space junk. Meanwhile, companies and governments pay exorbitant prices to build a similar spacecraft and put them in orbit.