You'll find yourself in a room with a Bench, Store, and some leapers/slashers. Get ready.
You'll get some dialog about fixing an elevator, head out into the zero-gravity environment and head below the giant elevator/cube. Shoot the thrusters below it to get it blasting upwards and into the correct place.
Then head back, preparing for a fight with some creepy Necromorphs.
These things will break into your elevator en masse, just shoot their arms till they back off. You won't die from lack of oxygen, so just worry about killing these things.
After thats over, you'll be dumped into a room full of cysts and some lockers. Keep an eye out.
The fun part: You meet an evil AI called ANTI who's an annoying bitch and tries to kill you.
Take the poor guy "sleeping" on the bed and make the door scanner to the left of where you first met ANTI scan his corpse to let you inside.
ANTI will realize your shenanigans and try to kill you with laser traps, throw something or shoot the trap to get rid of it.
When you get to the next room, ANTI will fuck you over by placing you between the glass and releasing necromorphs. Just shoot the triangle.
Once completed, hack the nearest terminal to power the cargo lift so you can proceed.
Tiedemahoweveryaspellit will open some dialog, just ignore him.
When you proceed, ANTI will then shut off the air supply, leading you to face a few Stalkers. You need to hack a terminal at the end of the hallway to turn on the air.
You'll pop up into the mainframe. ANTI will be there spouting some stuff about you to stay away, just keep going. Some minor puzzles here.
For now, you don't need to touch this yet, just head into the crawlspace.
Take all the plugs and put them into the right outlets till they're all green so the console which you can press shows up.
Some Enhanced slashers will show up. Dispatch them, then go to the other side by rerouting the crawlspace and repeat what you did.
Once you completed the 'puzzle' the circuits will show up. Punch them all till they explode to shut off ANTI and move forward.
After some Necromorphs, Ellie will hold a dialogue and you'll proceed down a hallway. Beware of some cysts.
Then you'll come onto this room filled with leapers, lurkers, and slashers.
Take that power closet for some medkits and credits. Save here, it'll be hard from now on.
Hack into the terminal and prepare for some spacewalking!
Nicole will yell at you again, after that ends press the blue terminal (already pressed here) and exit the door that unlocks.
You'll open the door into space, quickly press Alt to unlatch and fly over to that mirror in the background.
Click E on the mirror's console, that'll start Kinesis, just drag the mirror so its light aligns with the panel to the top right.
Keep an eye on your oxygen, if it goes below 30 seconds then get your ass to a station or you run the risk of dying.
Once you hover over to the second mirror a glowing baby Cthulhu will arise and attempt to throw homing squids at you. It's a waste of ammo to shoot down the homing missiles, so just avoid with Shift+Direction.
Shoot the big yellow bulbs to kill it, which it'll drop a Ruby Semiconductor worth big $$$.
Then, go up and align the second mirror.
The Solar Array will then power up and you can head back to the station to continue.
After heading back to the station, you must press E on a "door", really a chair, to propel Isaac into space! Yipee!
The chair will project Isaac at the speed of light, from which you'll have to avoid objects or Isaac will be turned into paint.
After a cascade of easily avoided objects and a tube, you'll be shown this mean mother hubbard, simply head into the green chute to avoid staining this huge debris.
Correct avoidance of becoming paint is shown here.
Once you survive the biggest piece of debris you'll be hurled into the space-city incredibly fast. Aim for the glowing tower, you honestly can't miss it.
After some tumbling, Isaac will then land in a pretty epic way, some lockers and medkits will be available to you, including a Store and a Save Station.
Continue into the next room to be reunited with Stross and Ellie.
After dialogue, the room will lose oxygen and Necromorphs will attack you until Ellie opens the door for you (just survive, it takes about a minute.)
After opening the door, you get to see Ellie's face and hear Ellie's whining.