Eradicator/Satellite Control (F3)

The objective of this level is to retrieve data from the three Ioxian moons using the satellite, which is done with a large combination puzzle similar to the three-switch combination lock you did in an earlier level. This level is probably one of the least complex in your main mission. There's a large central room with the satellite control which is the console with four switches, and three unpowered doors. Past the unpowered doors are three additional rooms with large monitors that for now won't be displaying anything. There are a couple additional rooms and a circuitous route around the level.

A few new enemies make their first appearances in this level. One is the Skeevin: these guys become very common and drop #4 ammo, making #4 your most useful "generic" projectile weapon. Another is the Gryklaan: they swim around in that green bio-muck and usually stay submerged. Sonic Shock Cells (#3) work especially well for taking these out. Also, a different version of HSD that has a flamethrower and drops #6 ammo, instead of the ones that shoot projectiles, is down in these lower levels.

Clearing out the area
First, go through the level and fight off all the enemies. Everything is accessible and you shouldn't have a problem with finding your way around, although things tend to be one-way in some places. While you're doing this, a few secret areas can be gotten to. In the room where you started, go to the corner diagonally opposite the level entrance, and activate the column with pipes and stuff. There's a secret area behind it. In the monitor room next door with the long straight walkway, activate the half-height console on the wall near the monitor. There's another secret area behind here. The third's a bit tougher. In the satellite-control room, you probably saw a shootable switch behind the control console, facing the powered-down door nearby. Go to the monitor room with the diagonal walkway (past the door by the switch), to the hallway beyond, and stand in front of the barred-off alcove. From here, shoot at the door in the monitor room to open it. You should be able to hit the shootable switch from here. When you do, the bars are opened briefly. Inside is a secret area with a Secret Level Access Keycard and a full-health.

Combinations
After you get the level cleared out, go to the satellite-control console. You'll need to try various combinations until you get a "satellite tuned for..." message. There are three combinations, one for each moon. When you find one, the door to the room with the appropriate monitor will power up (you won't have to try each room this way). Go up to the appropriate monitor, which will now be displaying one of the moons, to collect the data.

When you've tuned into all three moons and gathered the data, your task here is completed. Go to the side room underneath the overhead walkway in the satellite-control room, where a teleporter has opened. This is the level exit. But first, one more secret area. In the monitor room with the zigzagging walkway you probably saw a small door up in one corner. Now go to where the exit teleporter is, and look for a floor-plate switch like the ones in the previous level. When you step on this, that door is opened for a few seconds. Step on it, then quickly run to the monitor room and jump to the walkway from the ramp, then to the door and compartment inside. Inside is your first Death Sphere! (Don't be too bashful about using these, even though you can only carry one at a time. Nearly every level from now on will have at least one; many have two or more.) When you've done everything you want here, go to the teleporter and exit the level.