Ice rockets earthside
Next Fire Turtle tried to make a pulse jet motor out of ice injected with propane. Alas, the exhaust came out a hole melted in the side instead of the hole intended. If you look closely at the start of the side view portion of the video (the second half), you can already see the flaw in the casting where the ice is thin and the hole will appear:
Having looked ahead to a future when the economics and technologies become propitious, my own proposal was to take a grinder to an ice cylinder floating in space, melt the resulting ice flakes into water, and feed that liquid into a solar thermal rocket engine. The small snow-cone machine would gradually eat up most of the ice on the multi-year voyage from comet (or Ceres, or similar) to market. Alternatively, ammonia might be extracted from the comet and stored as a liquid inside a tank made from water ice, adding complication to the extraction process but greatly increasing the efficiency of the rocket motor and thus the mass of water ice, ammonia, or other comet stuff brought to market. More explanations of these icy and muddy daydreams lie here. When I was a kid in body as well as at heart I just stomped around in mudpuddles.
The ice rocket could in that future eliminate the need to launch from earth not just rocket propellant, but also propellant tanks -- or more precisely substitute a much lighter coat of sealing paint and sun shade for the tanks. A well-shaded vacuum can become extremely cold, preventing the ice from sublimating away. After propellant, tanks are by far the heaviest and bulkiest items that today must be launched out of our planet's deep gravity well, and ice rockets could substitute native materials for both.
Meanwhile, it's all just good clean terrestrial fun.
P.S. I also like the search engine.