[sjburt]

I thought when they were "flying teakettle" they were using water as a reaction mass, and the Epstein drive was an unexplained reactionless drive? At least in the books, haven't seen the TV show.

Iirc, there's some mention of pre-Epstein fusion ships that needed even more water.

[roywiggins]

It's left intentionally vague, but at some point they do refuel the drive. It's meant to be an improbably efficient fusion drive.

The alien forces demonstrably have a reactionless capability though (see: Eros) that utterly outmatches the Epstein drive.

[jerrysievert]

you can read the novella Drive online: http://www.syfy.com/theexpanse/drive/prequel.php where it appears to be some sort of issue that occurs to his failing fusion drive, so definitely a more efficient fusion drive.