It's been forever since I've played that, but if I'm not mistaken you just have to get a ship to that spot. In the middle VERY top of the screen you can see the sector reading, and that's one of the most important facts for this mission. I didn't know how to find the sector and so just flew around until I got lucky!

Anyway, yes, just constructors and getting ships out to that sector -- that's the real key. Don't worry too much about development because it's almost entirely irrelevant.

I might have overstated my lack of development. It's not that I didn't do anything. I especially worked to colonize planets that would get me nearer to 1-3 and make standing starbases, the easiest or targets, less essential. Of course I built factories and starports on planets to get colony ships and constructors out and about, as well. I don't think I built up any military, though. Or if I did, I didn't need to.