Spoilers!
The aethernauts are a group of scientists you meet in Act I. After discovering a mysterious hole underground leading into the void of space, they set about 1) plugging the hole, 2) building gear to protect themselves from the dangers beyond, and 3) exploring.
Prior to the beginning of SRPG, they ventured out from the mysterious wormhole, which as fate would have it is located not too far from the moon. Seizing this unprecedented opportunity, they naturally tethered the moon to their viewing station and created a gondola to travel back and forth from it. Over the years that followed, they established a small, semi-autonomous base on the surface of the moon to continue their explorations.
Things were fine until they detected a strange meteor impact and sent the lone lunar aethernaut to investigate. He didn’t come back, but someone else did.
The Baron.