SETTLING OFF EARTH
- transitioning to an ever expanding settlement -

A large lunar and Martian settlement could happen a lot earlier than many would anticipate. The key technology that would make this happen would be SpaceX's Starship. Not only would it be large enough to support a rapid population growth but, more importantly, a fully-reusable launcher would mean that the ticket price would be low enough to allow a very large number of people to afford to move off Earth.

Increasing the number of people who can move to the Moon involves three things:
    - Affordability
    - Number of launch sites
    - Frequency of launches
    - Number of passengers per launch

AFFORDABILITY
The significance of a fully and rapidly reusable rocket has frequently been described in this way. Imagine how much a plane ticket would cost if passenger jets were not reusable. Each trip would require the construction of a new airplane much as we have been doing with rockets. But a fully reusable rocket requiring not much more that refueling means that the trip will be much, much more affordable and, as the price comes down linearly, the number of people that can afford it goes up much more.

NUMBER OF LAUNCH SITES
Right now, SpaceX is using one east-west launch site in Florida and is building another one in Texas. With time, Elon has indicated that ocean-based platforms will be where most of the launches will originate from. And SpaceX has already purchased two oil platforms which will be their first two ocean-based launch facilities.

FREQUENCY OF LAUNCHES
SpaceX has stated that it is their goal to get their partially-reusable Falcon 9 launching as frequently as every day (load and launch with minimal inspection). Right now it typically takes something like three months between launches of the same rocket. But SpaceX is developing a tower with arms to catch Starship while it is returning to land. The purpose of this is not so much to eliminate the need for the rocket to carry the landing legs but so that they can quickly place the caught upper stage Starship upon the Super Heavy booster in about an hour. With rapid refueling, they hope to launch several times a day.

Elon has set as a goal to produce a fleet of 1,000 Starships with the associated Super Heavy boosters, tankers, and propellant depots. They are currently building the factory to make the engines and bodies in rapid fashion. Based upon progress being made, 1,000 starships over a period of five to ten years seems achievable. This many Starships with multiple refueling launches for each Starship would require many launch sites.

NUMBER OF PASSENGERS PER LAUNCH
Starship is stated to be able to house as many as 100 passengers at a time on trips to Mars. This seems a bit tight. But 100 passengers for a 3 day trip to the Moon seems doable. Indeed, perhaps it could take more than that due to the reduced travel time and the reduced provisions needed.

PUTTING THE NUMBERS TOGETHER
1,000 Starships with, say, nine tanker refueling flights per Starship every 26 months means that SpaceX would need to be launching about 12.5 launches per day. If each launch site were to complete three launches per day then SpaceX would need all of four launch sites. This seems more than doable.

1,000 Starships carrying 100 passengers per starship over 20 years would result in two million people moving off Earth. Elon's goal would be to have one million people on Mars over a 20 year period. But some of the ships would need to be cargo missions until production of bulk products could be produced at destination. Our assessment is that SpaceX's place and rate of progress makes what would normally seem like a crazy vision something that might actually be able to be achieved.