Here is phase 3 in NASA’s plan to actually send a person or people to Mars:

Then there’s phase three, or Earth Independent – the name gives away what the idea is here. It includes manned missions to the Martian moons and eventually the Martian surface, and once we’ve set foot on the Red Planet tests and experiments can begin to figure out how best to establish life. By this stage, missions will need to be self-sustaining, with minimal reliance on people back home.

It is likely that actually doing this would involve one of the newer propulsion systems they are experimenting with such as the EM Drive.  The tests are early but the results came back as an early success.

How far away do you think this would be?  Or perhaps you have some ideas on additional phases?

Feel free to comment with your thoughts.

thanks to sciencealert.com for the great info