I was pretty sure I had beaten this on Normal, but looking through my old computer I couldn't find any evidence of it.
So, I decided to give this a try again. After a few restarts just to get the feel of it, I got pretty far before the AI's Adv Lab took a blow and I won..
So is it possible to do this on Normal ?
Unless a disaster screws over the AI, I think it's very improbable.
You can pretty much hold your own until Mark 600 or so... but after that you will have not have the resources to deal with the increased size in waves. GP's will hold up until then, but when RPG's start rolling in, you need mobile units as backup and the problem lies in getting those.
After a couple of games with game speed pretty much 3 or 4 at all times, my guess is that your initial population simply is too small. At least I'm struggling to get above 20.
With that small amount of colonists, you sooner or later have problems running the very basics of your base, not even counting the part where you actually have to start building stuff from your SF or your VF. Personally I had to idle Nurs + Uni to actually get GP's out.
My theory is that the initial population is too small. If it was increased to something like 25-30 it might be possible to pull this off. Your still looking at a slow game with a huge amount of micromanaging though.
======================================================
What I did, was to reset the game until I got a 3 bar in the Southwest corner and used that for ore income. Reason for that is that while you may spend twice as much time getting back and forth between mine and smelter, you still get more ore in the truck per run. One possible setback of this, is the late arrival of the SF. (To avoid Pathfinding problems, I manually guided the truck back and forth)
Once SF was up, I get residence, nursury and university up, placeing buildings to get closer to my mine. At this point I set up another smelter closer to the mine, to avoid wasting time on the truck going back and forth and to stabilize ore production. Once that was ready buildt, I got a Vec Fac kit going in the Struc Fac and got that up asap.
From there I got one more convec before idling the VF again. (Permanently as it would prove later). Then I got up 8 GP's to defend my base. Time was of an issue when getting the first 3 GP's up, so I had to sacrifice to of my most damaged laser lynxes at this time. Leaving me with 2 undamaged lynx' (1 being my Railgun).
From there on, the GP's pretty much handled the inc waves until the RPG's started showing up.
For defense, I let my Railgun lynx deal with incoming attacks, moving back wards and using range to shoot down inc attacks.
As for the base, as already mentioned I had to idle nurs + uni to actually produce anything in factories. Often I would have to leave my agridome off aswell due to population shortages. So, for my part, the population is the limiting factor to this scenario.