The concept of alternative fuel sources is very interesting, and it will enrich the game. Alternatives to Hydrazine provide more paths for players to advance and explore the game world - introducing a lot of choice I think everyone will enjoy. Ethyl groups in general are common substances in chemistry; coming from organic fermentation, or extraction from natural gas in the form of ethane. It would be weird not to have some given its ubiquity. Natural gas ties into a former suggestion of mine: Gas Hydrate as a mineable resource. Early sources of Ethanol could be made from fermentation (as @individual-1 suggested; maybe with Carbon Dioxide byproduct); later on in game progression, players reaching outer planets/moons find and refine Gas Hydrate into Petroleum/Ethanol. Perhaps there would be distinction between both, one being Bioethanol, and the later Petroleum; however, serving the same purpose. That way Ethanol fuel sources can be used on both hospitable, and inhospitable planets (biosphere vs. anti-biome planets). To expand Ethanol uses even more... Ethanol, much like Isopropyl Alcohol, can sanitize. Both are solvents that dissolve lipids; the substance many microorganisms are made from. Suggestions have been made to introduce Space Diseases, or some kind of evasive parasite that preys on Astroneers. Combined with another suggestion, a Terrain Tool Projector Augment, Astroneers will spray down hostile biomass, or parasitic creatures. Think the Facehugger from Aliens, but instead of guns, Astroneers just slash the little beasties with a dose of super space hand sanitizer.