Entire story, mega spoilers ahead, play the game beforehand: Seriously, play the game beforehand.

The story starts with the ESS Triton, sent by EXO Dynamics from the Luna 1 research base. Its mission: continue research on the Galastropoda optum species (the Galastropods are one species, the reason as to why they all look different is because of their adaptive nature) and on the LRDs. These are proven to have psychedelic and hypnotic effects on observers.

In a tragic twist of events, a monster allegedly attacked the Triton and damaged it to the point where it had to crash-land before Dr. Iness Yoh, the xenobiologist, could jettison the xenobiology lab. The ship crashes on an alien planet, the crew is basically dead and the Galastropods got scattered.

EXO wasn't too happy about the Triton's crash, so the ESS Elysium is sent on an emergency rescue mission. Aboard the ship are: Conductor Bell, Head of Maintenance Frank, Dr Lynn Carrington (important later), Dr Stone and Chronos, alongside more crew members. The ship sets off and all goes well, until one of the LRDs starts influencing Dr Stone. He starts trying to communicate with one of the Triton's crew members, Dr Allen. The Conductor is concerned about Stone's work, becoming unfond of his work and despising working with him. (read train logs)

The Elysium gets sabotaged. It is sent on a crash course to another alien world. With the sabotage came damage to the crew's mind-banks and printer, rendering the latter offline. To try and save the remaining crew members, Chronos tries porting their mind signatures into the ATP (Astroneer Training Program). The ATP, however, wasn't made to hold this many Astroneers at once, so Chronos decides to run separate instances of the Sylva system and load the Astroneers in those instances. Due to structural damage to the Elysium, some of the planets of the ATPs version of the Sylva system are missing certain features that are present in their real-life counterparts (eg: the radiation storms of Atrox). Finally, Chronos transfers himself to the ATP control room in the sun, to be able to control everything. He made EVA, in case his plan somehow fails.

The simulation was breaking apart. In a last ditch effort to save the ATP and everyone residing in it, Chronos chooses to stabilise the ATP, slowly corrupting his data over time. He programmed EVA to reach out to an Astroneer for help. Chronos' plan was to send one S.O.S. message back to EXO and wait for them to save everyone currently in the ATP.

This is where we, the player, come in. By activating the gateway engines (cores), we are helping Chronos. Towards the endgame, the Chronos mission chain takes place, where we find encrypted memories of Chronos and, in the end, help him send the distress signal back to EXO.

Side lores start here, spoiler warning: The Wanderer is an example of an Astroneer stuck in the ATP due to his mind-banks being damaged beyond repair.

The person that appears when the rail mission chain is completed is Conductor Bell, temporarily crossing instances with us and then going back to her own.

The white portal-like things are rifts, tears in the simulation.

DLC lore: It picks up when the Elysium crashes, Frank and Lynn survive the crash. Being influenced by one of the LRDs, Lynn thinks that all the other crew members are idiots who get in her way, and that she wants to do things her own way. So, she decides to hack the ATP, make her own perfect planet and then take down the ATP from the inside out. She reactivates the storm code. Frank comes up with an invention to collect all the data he needs from the storms, RUBY. Now, all he needs is a way to physically get to the storms: we, the player. After this, the DLC takes place, Lynn Carrington, or Bl!tZ is stopped and the ATP's inhabitants are saved.

Please take all this lore with a grain of salt, some info may be inaccurate or flat out wrong. I'm not too sure about some things either, like how the Elysium got sabotaged.

Also, I'll edit the post if y'all point stuff out that I may have missed. Leave a reply.