Even in orbit, there is some air, even though it’s so thin it’s virtually non-existent. However, it’s enough to provide the drag that eventually caused Skylab to fall out of orbit. It was uncontrolled, and crashed somewhere off New Zealand, I believe. It was quite an event, and there were warnings along the crash line. There have been other notable dangerous deorbits.
An important lesson was learned: If a satellite is inserted into orbit, a means must be provided to fire engines to slow it down and crash in a controlled manner, into an ocean somewhere. In fact, for private ventures, the companies that fly the birds have to have the money in escrow at launch time, in addition to the propellant on board the crafts, to properly deorbit them.
I worked for the company that put the Iridium system into orbit to service world-wide telephones (call ‘em satellite phones). The system when belly up, so the plan to deorbit was put into play. It was already paid for. I don’t know what eventually happened to Iridium, because my section of the company left that section. It might have been sold before they crashed the birds, I don’t know. There were dozens or satellites, IIRC.
Thanks for the comment, Cyber Liberty. Very interesting.