Not long now
Chucklefish previously said that the beta for Starbound would arrive this year and with November nearly upon us, we're getting close. We must be! Indeed, the studio is now saying "it's really not very far off now." In a blog post, the three-stage beta was detailed.
Stage 1 will be the messiest of the bunch, with constant updates and the possibility of losing character or universe data. In other words, it's meant for folks who like providing feedback or simply can't wait to play Starbound already. I know that feeling all too well.
Stage 2 of the beta is planned to be more optimized and essentially feature complete; the sandbox experience will be in there and playable. Lastly, Stage 3 is when the main quest line will start to take form as Chucklefish nears v1.0.
As a reminder, a $15 pre-order of the game is all that's needed to secure beta access. After hearing these plans, I think I'm going to stick with stage 2 at the earliest.
How the Beta is going to work [Starbound]