First of all thank you very much, your comment means a lot to me.
Then, I find your comment a bit surprising because I thought that your build up was very good. As I told you in my comment, I let myself embark by your music.
I'm glad you noticed the transition at 1'11". I made several attempts to try to make the first part stick with the second one and I'm pretty happy with the result :)
To tell you the truth, I had to spend 2 hours doing listening research and watching sound design tutorials on the theme of space. Then 2-3 hours configuring my DAW to get sounds I like. Then 3-4 for the composition. And finally, one hour for the final mix. So about 10 hours (I had three evenings free this week, it was ideal).