It's still much cheaper and easier in the long run to build one launcher big enough to do a straight shot from Earth to Mars or other target. You have all the a

It's still much cheaper and easier in the long run to build one launcher big enough to do a straight shot from Earth to Mars or other target. You have all the assembly done on Earth and put all the lift capability into a single hyperbolic trajectory straight to the target, instead of doing on-orbit assembly (which we know how to do but is still outrageously harder) and devoting a lot of launch capability into putting mass in a circular orbit in an orbital plane around the Earth that's constrained by the launch site latitude, only to have to counteract a lot of that Delta V to put that mass onto a new hyperbolic escape trajectory along a plane defined between Earth and the target once it's put together. I believe SpaceX is planning on developing a still more powerful heavy launch rocket that could shoot human crewed missions straight to Mars in a single shot. The Falcon Heavy could send a substantial payload to the Mars surface.