Step-by-step instructions for making a two-way teleportation system in Subnautica Below Zero. Allows bi-directional travel between your main base and a Seatruck (or another satellite base).
Principle of Operation
Each time you generate a Teleportation Module, the game remembers the order in which they were fabricated. If more than one Module is powered, activation of the Tether Tool always takes you to the location of the oldest Module. If you shut off power to the oldest Module, it sends you to the next oldest. Thus the principle of this system is to temporarily disrupt power to the older module in a way that automatically recovers unattended. This is accomplished with various power-producing and consuming devices in the game.
Basic Set-up
Build a Multipurpose Room near (but separate from) your main base. Attach a single Solar Panel, which produces 75 energy/minute. Also attach a Seatruck Dock containing a plain Seatruck (regular batteries, no upgrades) with the OLDEST Teleportation Module. This Seatruck and Module remain in the Dock permanently as your main base's home teleportation station.
Inside the Multipurpose Room, build a Water Filter Machine and a Jukebox. Let the Filter produce water and salt, but do not remove them. This insures the Filter draws no power until we want it to.
Build a second NEWER Teleportation Module and attach it to your main Seatruck that you use for exploring and collecting. Your Seatruck must be powered. You'll also need a Tether Tool with Ion Cubes.
Basic Operation
To activate the system, wait until night. Then remove 1 salt from the filter. The filter draws 51 energy per minute, so drains the Panel batteries in about 88 seconds. Unfortunately the Filter stops drawing power when total energy reaches zero (to prevent activating emergency power). So to push things over the edge, you also need to turn on the Jukebox, which does not stop drawing power until emergency power activates. Once the station goes dark, activate the Tether Tool. It will take you to the Module on your main Seatruck.
To return to your Main Base, wait until day. At this point power at the home station is restored and the Water Filter resumes filtering and the Jukebox remains off. The panel produces enough power to refill the salt in the filter in less than one day. So from this point forward, the system is reset. Activation of the Tether Tool will always return you to your home teleportation station.
Advanced Options
1) Add a Sleeper Module to your main Seatruck. This allows you to immediately reset the Tether destination to home by sleeping after you arrive at your Seatruck.
2) Add 7 Flood Lights to the top of your home teleportation station. These will draw 7 x 12 = 84 energy per minute, which exceeds the Solar Panel power production rate (75 energy per minute). However, Flood Lights shut off automatically when room power drops below 15 energy. Thus they don't impact the operation of the Filter, but they do prevent the home teleportation station from ever having more than 15 energy. This dramatically shortens the time you have to wait to activate the Tether Tool after removing salt from the Filter.
3) Link your main base to a satellite base. If you have a satellite base somewhere, add a Seatruck Dock with a plain Seatruck, and attach a THIRD Teleportation Module. If you detach the SECOND module from your Seatruck (causing it to lose power), you will then have bi-directional travel between your main base and your satellite base. To re-establish travel between your main base and your main Seatruck, simply reattach the SECOND Module.
4) Add an infinite Ion Cube source. In your main teleportation station, add a Fabricator, Recyclotron, and Locker containing extra Ion Cubes, and at least one piece each of Lithium, Gold, and Silver. Each time your Tether Tool reaches ⅓ capacity (usually the case after one round-trip), replace the Ion Cube with a fresh Ion Cube. Then take the depleted Ion Cube (with ⅓ remaining capacity) and fabricate an ion battery. Then put this battery immediately in the Recyclotron to get back the Silver, Gold, and Lithium, plus a fresh Ion Cube with 3/3 capacity! This allows renewable two-way travel for as long as you want!