I do that using a combination of different mods like mekanism and thermal expansion. I setup an oxygen collector farm on the overworld, then have the collectors pumping out oxygen gas to mekanism condensators to turn it into a liquid, pump the liquid oxygen through a thermal expansion tesserect, and then turn the liquid back into a gas on the tesserects other end(the airless planet/moon) and pump the gas into sealers or bubble distributors... only issue with this method is you need ALOT of collectors and top tier pipes to make up for the gas to liquid bottleneck when having alot of oxygen using machines active. That and the chunks the collectors are in on the overworld need to be loaded 24/7 as well or this doesn't worki was hopeing their was a addon that would let me generate oxygen in say the over world and use something to transfure it dimentionaly kind of like a tesseract if their is a addon or if someone can make one for this it would be appreciated