My manuscript?

I would always recommend approaching literary agents first. There are some smaller publishing houses that will look at unagented submissions, but to go down that route you'd better be savvy when it comes to negotiating all the legalities in your contract.

If you haven't already done so, get a copy of the Writers Market and start researching which agencies accept science-fiction submissions, and what their submission guidelines are. You should also visit the Query Shark Blogspot for help in how to construct a decent query letter.