Each XSTN-K gives a special buff related to the way of obtaining them when equipped and permanently installed. They are also used for getting past The Barrier.
Right along the wall around the core you can find a hidden mass system with therein 8 asteroid stations in a circle, numbered from I to VIII. That's related to the 8 Xsotan Artifacts you can find (aka XSTN-K numbered from I to VIII). When you have all 8, and you put each in a separate ship, and park that ship in front of the asteroid with the number of the artifact it has, a jumpgate to the core opens (see The Barrier for more information). Things leading to those artifacts can be found in sectors with a hidden mass signature (equip a radar upgrade).
Note that you don't need to do these in the order the artifacts are numbered.
- I: Project Exodus - Acts as a teleporter key to open Ancient Gates when equipped; Permanent installation is not necessary to use the gates.
- II: Researched at the Research Station with 3 Legendary modules (maximum 1 XSTN artifact) - Give +8 to Armed or Unarmed Turrets when permanently installed.
- III: Pirate Captain Swoks - Gives +10 to Armed Turrets when permanently installed.
- IV: Sold by the Traveling Equipment Salesman - Gives +10 Unarmed Turrets and +45% Cargo Hold when permanently installed.
- V: Artifact delivery quest - Gives small bonuses to nearly every stat when permanently installed.
- VI: the AI - Removes requirements for pilots, miners, and gunners when permanently installed.
- VII: MAD Science Mobile Energy Lab - Gives massive energy bonuses when permanently installed.
- VIII: Bottan the Smuggler - Gives massive hyperspace bonuses when permanently installed.