Wait until the Heavy Trooper is below a container, then shoot the container and it will fall on him and, just like before, make him expose the fuel tanks on his back. Shoot the tanks, and then reload while you look for more cover and repeat the process until he is finally dead. Follow the waypoint to the ladder and climb up into the complex.
Kill the Helghast (you should be pretty good at this now) and look out for a weapon that will make the next few sections incredibly easy. It's the VC5 Electricity Gun, just like the one used by the Heavy Weapon Trooper you've just killed.
This beauty features infinite ammunition supplies and can zap entire groups of enemies at once, and at a decent range. Do not swap it for anything else until you are forced to because you've got some big, fat, killing to do. Take the ladder up into a transportation bucket and get taken to the next section.
Although you can reload the Electricity Gun as often as you want without having to find any extra ammunition it does take time to charge to full capacity, and so you'd be advised to press reload whenever you have a free moment.
The more frequent the reloads, the less time the reload will take. Duck into the transportation bucket and pop up to unleash electric death on every Helghast you encounter. Look out for a blue box that should be zapped to allow you to continue on your way. The bucket will open and you will fall to the floor. With the Electricity Gun at hand the next section is super simple.
Follow the waypoint to the lift while using the Electricity Gun to take out flying Sentry Bots with incredible ease. Take the lift and swap to pistol to shoot any spiders because they've been mutated by the mysterious Helghan mineral and are immune to electricity. Meet up with Rico in Transportation Control where you'll also find some INTEL. Follow Rico to Central Observatory.
You've finally found Evelyn, Garza and the rest of Alpha. They are being interrogated by Radec and are about to be executed. Things are looking grim, but you won't have to worry about a solution since Rico will quickly lose his cool and charge in - guns a blazing.
He'll kill all the Helghast for you as Radec escapes, but his aiming is too aggressive and clumsy and some stray shots catch Garza. He's not going to get to the next section quickly, but if you have kept the Electricity Gun you'll have no problem following the waypoint, destroying multiple Sentry Bots and Helghast with ridiculous ease.
THARIS AERIAL DOCK
Fry more Helghast with the Electricity Gun and when Evelyn has unlocked the door to the tower go in and climb the stairs where you'll find a sniper rifle. Alpha are now being attacked by a mass of Helghans who are too far away for the E Gun to be much use, so snipe them while waiting for an ISA transport to take you back to The New Sun and feel slightly upset that Garza dies of his wounds. Damn you Rico!
MISSION EIGHT: THE CRUISER
The Helghast are bringing the fight directly to the ISA fleet that's orbiting their planet. Take the elevator up towards the bridge and be prepared for enemy contact as soon as the lift reaches its destination. Ready some grenades and use them on the Helghast infantry that will burst through a wall.
Then get back to using standard arms and standard tactics and be aware that these enemies will try and get close to work you over with knives so make sure you are never caught short reloading and reload as often as you can. Follow the waypoint onto the Bridge where you will meet Jan Templar who has a special request.