SpaceX's Interplanetary Transport System has a well-defined plan for getting to Mars:
- Launch the ITS spaceship into LEO
- Launch five ITS tankers to fill the spaceship's tanks.
- Launch the spaceship on a trans-Mars trajectory.
- Enter Mars's atmosphere, shedding most of the velocity aerodynamically, then landing usings its engines.
What will the plan for returning from Mars to Earth look like? If the spaceship is fully fueled from ISRU methane/oxygen, will it have the delta-v to get from the Martian surface back to Earth without refueling, or will it require refueling in Mars orbit?