Fitter's Octopus route with solid, early use of the Venom. Make the most of the Magrail, then replace with a HS-90. When clearing rooms, make sure to keep an eye on your main weapon's ammo count. Reload in between white air lock rooms.

Pick up an Assault Rifle for the second half of the mission. Should be able to keep your ammo constantly refreshed until you reach the spiral ascending reactor, where you can replace with dual wield HS-90s. In the last room, spam any remaining grenades as you exit the air lock.

Ammo management is key in this game. You should always replace your weapons before you run out of ammo. The default pistol is one of the worst weapons in the game. The Magrail is by far the best gun in the game. It kills any bad guy in one hit and kills helicopters in two hits (It actually does more damage than the rocket launcher!). You can also get collateral kills with the magrail. The venom is another great gun but it's mostly used to paralyze stronger enemies. Once an enemy is stunned you can melee them once to kill them.