Achieving that goal requires getting a lot of tonnage to Mars, so expendable rockets are a joke, a waste of time. Fairings too.
Scale matters -- large rockets are efficient. Avionics for a large rocket are no larger than for a small rocket and you gain gauge advantages with size -- you can afford thicker, more accurate castings and skins on a large rocket. (The same goes for trucks and ships).Their current Falcon 9 is close to a local maximum for a kerosene-burning rocket which is limited to a 12-foot diameter because of road transport constraints and its length is constrained by the skin thickness required to avoid bending.
Methane is a better fuel than kerosene -- a rocket goes further if it shoots gas out the end faster and a bigger percentage of its mass is propellant. Furthermore, oxygen is cheap and you can go to a higher oxygen/propellant ratio with methane and you can make both oxygen and methane on Mars.
He gave some timetable guesses with the caveat that they assume exponential innovation:
- 80-90% confident of reaching orbit with Starship next year.
- 50-60% confident of ship and booster reuse next year.
- High volume flights in 2022 -- each capable of launching up to 400 Starlink satellites.
- Refuel in orbit in 2022.
- Two or three years for a moon ship -- after refueling in orbit.
- An un-crewed Mars mission in maybe four years (at the time of the second Mars transfer window from now).
The above assume a non-linear rate of innovation. When asked what makes SpaceX so innovative, Musk first said "I don't really know," but went on to credit having ambitious sub-goals like:
- Full and rapid reuse.
- Orbital refueling.
- Propellent production on Mars.
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