Hi there!
Steam Greenlight is a great platform for indie games and its likely that Starsector will eventually use it (or other means to get on Steam). That time, however, has not yet come. Starsector still needs a bit to mature, I'm sure when it's ready the developers will make their move on steam. Here's what the lead developer said about the idea:
"Guys - I appreciate the thought, but I really don't feel like Starsector is ready for this kind of exposure. Please don't do anything on my behalf to make that happen - I think it could end up causing serious problems, both for the development of the game, the community, and, indeed, my mental health "
See also
this post by David, the art designer.
As a general advice: It is a good idea to use the search function (upper right corner) to see if anyone posted a similar suggestion before