Orbit's original stream of comics are in the public domain! And now the files that I've used for creating them are publicly available as well, so you can easily make your own!
Download the files and start making your own Orbit comics!
...there's not really much else to say.
If an Orbit comic is not in this repository, it is not in the public domain, although if characters have reappeared in newer comics that were in these comics those characters are still in the public domain. If you're unsure, just email me, I guess.
Read Josh Powlison's original Orbit here: http://www.webtoons.com/en/challenge/orbit/list?title_no=58078&page=2
Or check out Josh Powlison's serious stuff here: http://joshpowlison.com/