Finally - you've breached the defenses and arrived at the Core Generator of the MotherShip. It's not over yet though - the generator is heavily guarded, and even if you destroy it, it still doesn't get you off the planet.
You start between the doors by which you escaped from the previous map and another set of doors ahead. Go through these doors and be sure to collect the Flak Cannon and Searchlight beyond. You will be in a huge room with the equally huge generator in the centre. Don't go any further in yet though - read on first.
Let me try and explain this place to you. The generator is a large circular structure with three sloping legs you can climb. In the centre is an insta-death energy beam. Around the edge up above is a circular walkway accessible either by climbing one of the legs or going through one of the three portals at ground level.
Let me go through the gear accessible. At the base of the leg ahead as you start is a Health Pack. The next leg clockwise has in its vicinity a set of Jump Boots, a Health Pack plus a can of Tarydium Sludge beyond. The third leg reveals nothing. The raised circular walkway is more rewarding, with an Assault Vest, a Shield Belt and a Super Health Pack. The reason I've told you all this is because you're going to have to decide for yourself how best to fight the next combat sequence.
Time to fight... so go out into the room. A SkaarjLord will spot you from the left and sprint up the sloping support ahead. Follow him and flak him, thus beginning an extended combat sequence in which you have to fight several SkaarjLords. I made it about seven, but there were never more than two at a time. Make full use of the terrain, your armoury and the gear provided to kill all the Skaarj. You may think that you're safe once you've killed them all, but then it gets worse.
A door opens at one end of the generator complex and the Warlord comes out. He's back, and he's worse. But there's no running away now, no more places for him to retreat to. When you defeat him, he dies. So, it'll be a tough fight, but kill him (the Flak Cannon is probably the most effective weapon - if you don't mind using the ammo). When he dies, a lift descends from the centre of the generator structure. But don't take it yet.
In circulating round the giant structure, you may have noticed power-ups lurking on protrusions beneath the climbable ramps. To get to them, go up one of the ramps then drop off on to one of the intermediate protrusions from the central unit to either side. From there, it's a simple drop or jump to whichever item you want to collect. Visit all of the protrusions in this manner, and you can get hold of Jump Boots, an Energy Amplifier and a useful Super Health Pack.
When you're done collecting, go down to the floor and ride the lift into the core of the generator. Inside, you will see three energy beams. Shoot all three to extinguish them, and the lift starts to go down. As you descend, the level changes.