The wiki said it was obtained in the Dark Sector? Which is accessible through solar rails? I may have misunderstood then
The Orokin lab and Solar Rails are a relic of the previous Dark Sector system.
Dark Sectors used to be accessed through rails built and operated by clans, and those clans could set a material and credit tax. Clans could also fight over a rail and there were invasion style missions like you have now with Grineer and Corpus, but you would side for a clan.
The invasion missions themselves went through multiple iterations.
The first version it was PvP, with everyone starting with a rank 0 frame and weapons which would level up over the course of a single mission and as your gear leveled up your mods would come online. It was an unbalanced bullshit mess that was also fun in its own way. Unless there was an Ash or Valkyr on the opposing team, then it was just bullshit.
Eventually it was changed to be more like regular invasions, but the tileset was the Orokin Tower and occasionally NPC specters based on members of the clan you were fighting against would spawn in.
The system had major and minor changes throughout, at the very start there was no armistice period after a Rail was won over or successfully defended, and there was no way to play the normal mission while a Rail was contested, so some Rails that granted access to popular Dark Sectors were constantly under invasion and the sectors were inaccessible for weeks. Fun times.
There's a bit more to the story but those are the interesting bits in my opinion.
Eventually DE got tired of maintaining that shitshow, retired clan operated Rail system and so now Dark Sectors are just regular nodes on the map.
[EDIT]
Re-reading this it's hard to believe half the shit I wrote actually happened, kinda feels like a half forgotten fever dream that happened half a decade ago.
*checks calendar*
jesuschrist