UPDATE (4/6/17): Achievement finally popped while on my Hard Mode playthrough!
I beat the game on Easy (on August 30, 2016, FYI), and this never popped for me for some reason (It didn't even say "Done, Unlocking" on my Achievement List) and yet I was able to get the achievements for Completing the game on any difficulty, completing the game without dying, and completing the game without killing any humans. Weird.
But just saying that would not really call this a solution. So... here's a quick version (as quick as I can make it) of what to do. NOTE: I did this on Easy - I plan to do it again on Hard to get the Hard difficulty achievement out of the way eventually, so things might be more difficult than my guide may point out. You were warned...
Soon as you start Mission 17, you're in an elevator leading out into Solomons Habitation Tower - Habitation Decks. To your right will be a save station, but be careful - there will be a human guard patrolling the area, and he WILL shoot you! Either stay clear of him while you work, or kill him (which will attract the Alien), OR have him shoot at you and attract the Alien to kill him instead. I found the Alien to be easier to handle than the human (scaring it away with the Flamethrower or a Molotov).
No matter what you do, go to the corner where the Transit door is and to your left will be a sealed door requiring the Ion Torch to cut open the lever to open the door (WITHOUT attracting the Human or Alien). Soon as the door's open, follow the corridor into a small room with a terminal. Access the file marked "Code for Repair Job" as it has a code you will need (1851).
Note: on my Hard playthrough, the guard actually followed me into this room, so I had to use the Stun Baton on him, which still attracted the Alien, but thankfully it was still out in the larger room where the elevator was. I bided my time until it left and then moved on.
Go back into the main room and to your right is a locked door you can use the 1851 code to open up and go through. Follow the corridor, keeping in the center to avoid the metal detectors and setting off alarms, and at the end interact with the control panel in the center to restore power. There is another save station in this room, so use it if you will.
Head back to the main room once more and now you will be able to open the locked door by the first save station. Open the door, BUT have your Flamethrower ready - a Facehugger will "greet" you from behind several boxes inside the room. Torch it, then be prepared for the Alien to come looking for you. If it does, hide OR scare it off. If not, then count your blessings. Regardless, loot the room, and then interact with the console in this small room to get the transit back up and running. Move to the Transit doors and hit the call button. It will take a bit, so back yourself into the corner to the Transit doors' left (your left) and have your Flamethrower ready in case the Alien comes back. Soon as the Transit doors open, get inside and hit the
button when prompted to get the Transit going.
You'll arrive at the Habitation Upper Transit, but you won't be here long. Ahead on the right wall is an open elevator door. Get to it, but be wary of another Alien patrolling the room (but sometimes it's not there). Once inside, hit the button to move the elevator. It's a short ride, as the elevator gets halted and the door opens to reveal you have to traverse out of the car into the next area, to find an alternate route to the Spaceflight Terminal. There's a save station your left just after you get out of the elevator - use it.
Follow the hallway and deal with a Synth that approaches you (I prefer a charged Bolt Gun shot to the head), moving on through the hallways into the Cantina. An Alien might appear in here, too (persistent chaps, aren't they?). Duck-Dodge-Hide, or scare it away, then cross over to the terminal, noting the fully-loaded forklift blocking exit to the right of it. Interact with the terminal and read the file "Last Stand" to get another code (1984), which you need to use on the wall locker behind you and to the right. There's a keycard inside - take it and turn right around with the locker to your back to look for a standalone keypad on your left, waiting for you to use said keycard. This will unblock the exit enough you can crawl underneath the forklift's front. and move on.
Hang a left at the T section ahead of you, coming to a locked door. Use your Ion Torch on the panel next to the door to help open said door.
Now comes the "Fun" part of this mission - follow the hallway straight and as it curves to the left. Note the first (locked) door on your right in the first straight hallway - you'll be back here shortly. Keep going until you enter the Rec Room (take note of a darkened area with one place to hide if you need to use it, especially on Hard Mode) and stay to the right where there's a save station and a vent. Save your progress and take the vent into the next room (the Projector Room). Ready your Flamethrower as you stay right and enter a smaller room. Face left when you hear a shriek, and burn the Facehugger that tries to come at you. Once it's dead, grab the keycard next to the body in this room and retrace your steps. There's another keycard port in the left corner of the Projector Room. Using it will open not only the locked door you passed earlier in the hallway, but also the door connecting the Rec and Projector Rooms... as well as alert the Alien to your activities. After the Alien leaves (you scare it off or hide until it gets bored and moves on), go back into the Rec Room and save if possible before going back the hallway you came from, backtracking to the door mentioned earlier, which will now be on your left.
Inside the room along the back wall is another save station (you know what to do with it, right?). To the left is an open door into another room, but enter is with caution - the Alien will more than likely jump in through the semi-blocked door on the left. Chase it off or hide, and then go to the closed door with a lever on its right. Pull the lever...
...And the power goes out, keeping the door shut.
This is the part where you'd say "Well, that's just perfect! NOW what do I do? ...Wait a minute! There was a generator in the Projector Room, next to the door to the room that had that Facehugger and the keycard. ...do I REALLY gotta go back down that spooky hallway and through the Rec Room AGAIN?!"
Sadly... yes, you have to.
Backtrack to the Projector Room, keeping an eye out for your "biggest fan" the Alien along the way. Restart the generator and then, yep, go back one more time through the hallway and back to that room where you had to pull that lever. Thankfully, the door will be open this time. Inside and to the left is another vent - take it and follow it until you get out, take a left and then a right for the open elevator.
BIG note: If you exit the vent and see an open elevator on your right, DO NOT TAKE IT! This was where I messed up and thus I didn't get the achievement to unlock. Again, go to the LEFT after exiting the vent and take the other elevator waiting for you.
Hit the button to move onto the next area, where you hand to crawl under some debris, n left to take some stairs down and then head straight for a door you need to use your Ion Torch to access it's lever. Pull that lever to open a corridor leading to another elevator and the next chapter.
Mission 17, finished!