Long time player, first time cartographer.
The map is not unbeatable, just not a quick win. I tend to be a careful long term player and I think my first map reflects it.
No idea at this point of how prolific of a map maker I will be....
Now that Colonial Space is out, you should submit your maps there directly in the game, instead of posting them to the forums.
I hate to ask, how do you do that? I've looked around Colonial Space and Projects and haven't seen anything that says 'Upload'. What am I missing?
Upload is in the projects menu. First you submit a score on the finalized map to prove the map is possible, and then you can upload it to CS from that menu.
Finish your map. Finalize it in the editor. You'll see it in the list of Finalized Worlds (see picture). Play the map with the play button here. When you beat it, submit your score, and the red "Play Score" text turns into an "Upload" button. Click that and fill in the dialog.