Here is a flowchart for the program whose eventual, hopeful goal is to establish a self-sustaining colony on Mars. Tell me at which step you think it breaks down:
Build a huge rocket with lots of payload:
If it flies, go to next step;
If it doesn’t (now very nearly established that it will fly and not blow up, crash, etc.)
Make the huge rocket reusable:
If it can be recovered and reused, go to next step;
If it doesn’t, fly as an expendable booster which is still cheaper than any alternative out there for low-Earth orbit applications. (prospects for reusability now looking better)
Make the huge rocket reusable quickly and cheaply:
If the rocket meets its cost and cadence goals, go to next step;
If it doesn’t, it’s still cheaper than an expendable rocket for low-Earth orbit applications.
Establish that the reusable rocket can fly as a tanker to refuel Starship upper stages in orbit:
If fuel transfer works, go to next step;
If it doesn’t, you still have quick, cheap launch like Falcon 9 but bigger and cheaper.
Have a refueled Starship upper stage do an unmanned demo flight either round-trip to the moon or one-way to Mars:
If it works, go to next step;
If it doesn’t, you still have an enormous transtage and payload for one-way missions.
Have a Starship demonstrate the ability to support a crew in high orbit for the length of a Mars journey, about 260 days. 260 days in space is a modest goal that’s now well-established. The main deal breaker is dealing with radiation exposure beyond the protection of the Earth’s magnetosphere:
If it works, go to next step;
If it doesn’t, then manned interplanetary flight will be much harder than we thought. First real roadblock to Mars plans.
For all of the following steps the two defaults are:
If it works, go to next step;
If it doesn’t, delay next step indefinitely while the problem is worked on.
- Demonstrate that in situ fuel and oxygen production on Mars works.
- Demonstrate that a Starship can reenter the Earth’s atmosphere safely not just from orbital speeds but from interplanetary speeds.
- Demonstrate that a Starship landed on Mars can refuel in situ and return to Earth.
- Send first crewed mission to Mars and back.
- Set up preliminary Mars base; establish that a crew can live and work there for extended periods. Test food production and recycling efficiency. Measure long-term effects of reduced gravity. Debug equipment necessary for following steps.
- Start sending cargo missions to build up supply reserves to support expanded base population. Minimum is sufficient supplies to support all personnel until evacuation back to Earth if necessary becomes possible.
- First wave of settlers; expand base as logistics and finances permit.
- Keep the whole enterprise going. Reduce reliance on imports as much as possible.