That’s a solid line of inquiry. Plants convert solar energy into chemical bonds through photosynthesis, so their sugars are already a low‑toxicity energy source. The trick is getting from sugar to something usable in a spacecraft engine. One route is fermenting the sugars into ethanol or butanol, then refining them into liquid propellants. But the real efficiency gains come from lignocellulosic biomass—think algae or fast‑growing crops—that can be directly converted to bio‑hydrogen or biogas. Algae are especially promising because they grow in large, closed bioreactors, produce high lipid content, and can be harvested without competing for arable land. The challenge is scale: you need a tight energy loop—feedstock growth, conversion, and waste recycling—while keeping the system’s mass and power budget within launch limits. If you can hit that sweet spot, you’ll get a propulsion fuel that’s both clean and essentially free of toxic byproducts. Any particular plant or algae strain catching your eye?