The New System That Could ACTUALLY Replace Rockets

This system would be great at launching material into orbit with one system and for human transport with another, more gentle system. There should also be systems on the Moon pointed both to Mars and to Earth to send water or hydrogen and oxygen fuels to LOE. 

It or Starship could launch Lunar and Martian habitat modules (with equipment if weight permits) to be sent via some type of orbital maneuvering vehicle into an elliptical orbit to a lunar transfer orbit - without regard for when they land. Just fill the space until ready to install in mass. When ready, intercept modules when close to the Moon and circularize them and then, with fuel generated from Lunar soil (possibly with an autonomous system) land astronauts from the Gateway to transfer fuel modules to landing frames that they can ride up to modules and ride back down - one at a time, refueling on the surface. Also send up in a similar fashion a Lunar-mover to position individual modules into an interlocking habitat with another machine designed to bury habitat modules when linked up.

As you can see, job one is to land and install machinery to extract O2 and H2 and a frame to transfer what should be a whole collection of modules from orbit to the surface. The modules can be launched once designed with an assembly line ready to go. BTW - the same kind of assembly line should be developed to build both simple housing and housing with personal food production facilities (especially hydroponics, but possibly also mini-protein VATs.

Space Station modules (again with or without equipment) can be launched either by screw drive or by Starship - either inflatables or solids - for transfer to LOE and then boosted to a factory orbit for integration and boosting or placement for Earth or Mars Orbit (after we model and test rotational gravity systems). An orbital Mars colony would be crewed in Earth orbit and then boosted. It will take a ridiculous amount of fuel sent up from either the oceans or the Lunar surface, whichever is cheaper. Volume is infinite - meaning we don't have to worry about the size of the ship, just the mass. Inflatable bladders can hold reaction mass for an ionic engine system for the colony tug - which would then refuel from Martian soil (the habitat will remain in orbit) for return to Earth to tug another colony to either Mars, the Belt or one of the gas giants.

Early Mars equipment can be sent from a screw drive catapult from the Moon, with multiple launches in various orbits that can arrive at various curves to intercept Mars on either simultaneous or staggered schedules. Another option is to use Martian moons as a loading dock. With ion engines that worry about mass but not volume, we can build in flexibility.