Who thought the future would be giant chemical rockets (100x BFR?)thundering around the solar system? Transportation infrastructure for the solar system, Rail Road Tycoons of space. The potential is immense.
It's not. The math doesn't work, the rocket equation bites too hard. This is one of the reasons to be keeping an eye on the recent claims over the past few years that fusion reactors may be something that could be shrunk down to shipping container sizes in the relatively near future. Get a functioning fusion reactor into space and suddenly the solar system is, if not your backyard, something very reachable.
But it's possible we won't see any practical way to lift off from Earth other than chemical rockets for a while.
We really need to be able to get places in a couple of weeks, and chemical rocketry just gets absurd for that; even if you can do it, you've got to fling massive refueling stations around and such. A fusion-based system would have power density sufficient to not just fly to Mars in a reasonable period of time, but to fly back without having to be refueled, which means we can go places without first figuring out how to build a fairly expensive and massive infrastructure that allows us to get back.
If you really want something that can be put into production in a matter of years, then it would be fission-based rockets. Maybe they'll be more acceptable if they are not launched from Earth.