Oddly enough, yet another crashed dropship appears. There's another turret here, and although it's less powerful than the green-laser one you used earlier, it'll still get the job done on the three SBD's in the area, as well as the ones coming out of the Coreship corridor at the end of the canyon. Set up a soldier in the turret and another in the snipe spot nearby, then advance slowly towards the corridor with the remaining trooper, letting your emplaced squaddies kill anything that comes out. When you get close enough to the corridor, it'll stop spawning enemies, allowing you to enter, which will only reveal a shielded door. You'll have to find another way into the ship. Before you move on, though, don't forget to grab the anti-armor attachment for your gun near the crashed ship; it'll come in handy against most large targets that you're going to be running into.
Luckily, there's a fragile set of rocks in the valley where your emplaced troopers are, so return there. Another sniping spot has appeared, as well, immediately near the rocks, so set your third squaddie there and disengage the turret gunner and the other sniper; they won't have a line of fire into the next area from their positions. When the explosives are set, position your guys behind the sniper and blow them. There are plenty of baddies in the area beyond, so let them come to you and kill them as they approach, but let your squaddies do the heavy lifting; there's no sense in expending too much ammo or grenades on the foes when your squadmates can kill them all fairly handily.
Now, when the coast appears clear, you can start moving into the little arena here. There are two sniping positions, so immediately get your teammates into them, but stay behind the rocks here, as a Spider Droid is going to be coming out of one of the passages here. There isn't much your snipers can do against it, and it's only vulnerable in a small designated target area. The trick to beating it is waiting until you call out for an anti-armor position; when this occurs, you'll be able to command one of your squaddies to set up shop near the sniping position by the bacta dispenser. After that's done, all you really need to do is wait for him to blow the damn thing up. He will be taking fire from the tank, though, so try and stay behind him and help him out by using anti-armor rounds on the droid, or by sniping at the red ocular cluster from a safe distance away.
Hold Position For Gunship Support
After the Spider Droid's been dispatched, you'll be able to move up to the shielded doorway elsewhere in the area to trigger a conversation with Advisor that'll lead to the approach of a gunship. Unlike the rest of its brethren, this one won't crash to the ground and give you the convenient use of its turret; instead, it'll actually blow the doorway, allowing you to get in, but also allowing the hordes of droids within to leave. Only one of your snipers--the one closest to the doorway--will have a clean shot at these guys, so take the other two and start making your way towards the door and inside.
When you've sliced through the first interior door, you'll have to face off with another group of droids that are positioned on the far side of a long gap from you. They're far enough away to be pretty inaccurate, so set up one of your squaddies at the sniping spot and let him start wailing on the targets. The other pair of squaddies can help him out, but you'll eventually want one of them to start slicing the panel that'll extend the bridge. This will bring the droids closer to you, allowing you to finish them off before healing up and moving on.
Infiltration of the Core Ship
Navigate Through Storage Racks
Now that you've successfully managed to get on board the Coreship, your squad is going to be split up, with each of you responsible for destroying one of the ship's key components. Your task, for instance, will be to navigate through the storage racks holding the Super Battle Droids and shut them down. There are going to be a LOT of SBD's in the area, obviously, but luckily for you, most of them are in storage and dormant. They can be woken up, though, if you happen to bump into them or damage them, so try not to use any grenades until you're in the clear.
The first difficulty here will come in the form of a turret that'll fire at you from one of the walls; when you spot it, destroy it and proceed onwards a bit, but don't rush blindly ahead, because the destruction of the turret will have awoken one of the SBD's. Again, grenades are a bad idea here, so you'll probably want to run back to some cover, then use your sniper attachment to strafe out and pop the droid with headshots. When it falls, you'll be able to proceed through the gap it left in the storage racks and move on.
Eventually, you'll come to a bacta dispenser. The large hallway beyond this landmark seems nice and barren, but if you check the ceiling, you'll notice a turret above you, so destroy it. Although this'll set off the alarms in the area, they would've been set off after the turret noticed you anyway. Regardless, you'll have to deal with the appearance of a Geonosian Elite outside the window, so mark it with your use key to get its health readout before engaging in more strafing exercises with the wall. The Elite won't fly into the hallway, so you'll have ample cover, and you can easily backtrack to the bacta if you get hurt. When both the Elite and the turret are taken care of, plant explosives on the grate at the end of the hallway and move on.