In this page you can find walkthroughs of additional mission in Prey that can be unlocked while exploring the Life Support section of the Talos I Station. Completing those missions is completely optional, but you can acquire valuable items by doing so.
The opportunity to unlock this mission arises after reaching the Water Treatment Facility and dealing with the Typhoon Technopath (done during the Reboot main mission). Look around near the entrance to the facility (northern part of the room) for a note - it's located right next to the generator used to restore power to the station. Examining the note will unlock the described mission.
Your first task is to find the injector. It's located at Tobias Frost's corpse. You can find the corpse by going to the Security Station, finding Frost on the employee list and starting tracking, but this step is completely optional. Head back to level 1 and examine its western section. Notice the entrance to the toilets, covered by glue. Break the glue balls and look for the entrance to the ventilation shaft (shown in the first screenshot). Turn on the flashlight, as the area is dimly lit. Tobias' corpse can be seen in the second screenshot. Examine the corpse and you will receive Psychoactive Particle Injector (you can also listen to the TranScribe recording).
Head back to Water Treatment Station where you've started the mission. You must reach the room located above, in the south-western part of the station. Start by locating stairs. Go through the balconies to the monitoring station and either take out or avoid any contact with the elite Phantom located there. Continue your march west - your destination is the water quality laboratory. The main entrance to the lab is locked. It can be accessed by using Mimic Matter and squeezing through the narrow entrance, but it's easier to shoot at the windows (shown in the above screenshot) and using the Artax Propulsion System to get there.
There can be a corrupted operator inside of the lab - be prepared to take him out (it can also be done by attacking the machine when it stops near the window, before entering the room). Place the injector you've acquired earlier into the large slot of the central machine. This will complete the mission. From this moment onwards, using fountains and other places where you can draw water from will restore a small portion of your health and a minimum amount of psi as well.
This mission can be unlocked after reaching the security station located in the western part of Life Support, near the passage to Talos I Lobby. Security is closed but you can solve this problem with the Mimic Matter ability, turn into a small object and squeeze through the small entrance (you can also come back here later, after acquiring the necessary keycard). Once inside the security room, use the nearby computer and read the message about the missing engineer - Jean Faure. This will unlock the mission.
Before you leave the security room, open the employee list tab and search for Jean Faure. Start the tracking process, as her corpse is well "hidden" and even knowing the location won't help much, as reaching them is quite difficult.
Jean Faure's corpse can be found in Talos Power Plant. You must reach level -3 and enter the room with the reactor. If you've done according to this guide and started tracking the corpse, the object you're looking for will be marked in the southern part of the room. Reach the elevator shaft shown in the above screenshot by using multiple metal balconies in the area. You won't be able to use the elevator, but you should be able to see a small hole located behind the bars - this is your destination.
You must now reach another entrance to the elevator shaft, located on the lower level. This can either be done by going down the stairs in the northern part of the reactor lobby, or by carefully jumping down. Your destination is the area shown in the above screenshot (watch out for a Mimic that might be lurking in the area!). Press the button now - it won't let you call the elevator, but it will guarantee you access to the unused elevator shaft.
It's time for the most difficult part of the mission, as you must complete a climbing sequence towards the mentioned hole located on the upper level. This can be done by using the GLOO Cannon. Use it to stick glue balls into two neighboring walls and jump on top of those balls, slowly moving towards the upper level. You should often save, as it's easy to fall down. Remember to also use Artax Propulsion System and that you won't fall down if you don't land on the glue ball perfectly - in that case the protagonist will grab the "ledge" and climb on top of it.
Continue the climb until you reach the small entrance shown in the first screenshot. Don't be hasty, as there should be a Mimic and a Phantom located on the other side of the said entrance. Try to attack them from your side and get to the other side once they are down. You can now go through multiple corridors until you reach the corpse of Jean Faure shown in the second screenshot. Examine the corpse to find a neuromod and the keycard to Air Filtration Control Room.
Air Filtration Control Room is located on level 2 of Life Support section of the station. Get back to that location and go through the decontamination area on level 1. Watch out for Phantoms, corrupted operators and flames - the last one can be dealt with by using the GLOO Cannon. Once you're at your destination, use the keycard you've just acquired on the closed doors and examine the new room. Inside you will find another neuromod and Jean Faure's TranScribe.