I found this thread after googling for a solution, since I'd been stuck on this for a while, even though it really seemed like my orders were super optimized. I had managed, before the end of the 48h, to capture 3 enemy outposts and get enough drillers for a second mine – just not on the same outpost.
Turns out the key thing is to promote the existing specialist to Navigator right away. It then becomes super easy. I think that if you miss this tiny thing you're in for a lot of struggling that will amount to nothing. It's a shame that such a seemingly innocuous choice is what the whole challenge rests on.