The hardware we engineer comes from drawings that we draw directly in some cases, and also from the drawing tables and computers of industry companies like Rocketdyne and Aerojet in California. Mikey, for a ram jet, oxygen has a good density, and serves as the required oxidizer. Xenon has come into use for some forms of electric propulsion. Well, I will get my Ph.D., no matter how long it takes. We need to see many different elements of an engineering problem to make space flight doable.
Water electrolysis is a very doable and efficient process.
You have obviously been doing some studying in this area. Richard, the exhaust from launch vehicles is minuscule compared to automobiles and chemical plants. Nuclear energy is felt by many here to be the thing that will ultimately get us to being real space explorers. I personally am looking for young future space travelers like you to come up with something that no one has thought of. The connection there is slow.