The only viable means of rocket propulsion we have now is chemical, as you say, which is not very efficient to say the least. These rockets are enormous “flying bombs”. I was thinking more along the lines of a nuclear fusion system that does not require elaborate calculations to establish exactly, plus a few extra percent for eventualities, how much fuel is required for a round trip. If space research is mostly funded by the US military, it's surprising that, after so many years since the first moon landing, such a propulsion system has still not become a reality. Moving equipment and people to Mars will not be possible otherwise. I don't think that humanity will get very far off of this rock until a practical breakthrough occurs in fusion research.