While we should take this serious, I think is is very important to do our outmost to allow space exploration to continue. Remember without rockets launching satellites into orbit we would not have had climate science.

Long term space offers us an opportunity to move dirty industries off Earth, as well as solving resource shortages with asteroid mining.

I don’t know think clean fuel isn’t used today because it is too expensive or difficult but because it is not an important priority. Emissions from the space industry is simply not high enough at the moment to focus on green fuel right now.

Unit cost is a volumes game. Making green fuel is likely way cheaper at volume than the smaller volume we got now. There will always be fixed costs which will drive up units costs if you do this for very small quantities.

If CO2 is a problem then metal based fuels may be a possible solution as they basically just produce rust that falls down as by product. Only issue is that they are not great for reuse I would imagine.