SpellJammer was an
AD&D campaign setting that is indicative of the reason
TSR went
out of business. While it had some neat concepts, it had a lot of quirks and never really caught on with the mass of AD&D players. As a result, TSR sunk a ton of
money into producing the setting, with only minimal results.
The method of powering the SpellJamming craft was, for the most part, for a spellcaster to drain her spell levels to propel the ship. The problem with this, of course, is that it then made the spellcaster pretty useless in combat - and hence not nearly as fun to play. Being the pilot of the ship was kind of cool, but doubling as its fuel supply was not.
The system did have a kind of neat backstory. It revolved around wars between the Scro (basically Orcs) and Elves, with the evil, spider-like Neogi, Beholders and Illithid (Mind Flayers) thrown in. That would be standard fantasy fare, except that it's all happening while zipping around in space. It also provided a way to link Dragonlance, Greyhawk and Forgotten Realms campaigns together.
Spin off products include the books, which are mentioned in one of the above writeups (although the fact that at least one, Into the Void, was written by Nigel Findley is not), and a computer game, Pirates of Realmspace, which was quite a bit more fun than the pen and paper version.
Fantasy Flight Games is producing a new setting, called Dragonstar, which looks like it might offer a more manageable system for D&D in space, although they are taking on more of a high tech angle than TSR ever did.