SpaceX were founded as a space development company and aim to produce all the space technology needed to colonize Mars. This will require an extraordinarily capable launch vehicle and since inception they have continually increased the size of their vehicles to improve the payload delivered to orbit (i.e. Falcon 1: 0.18t, Falcon 9: 22.8t, Falcon Heavy: 63.8t through to Starship: 100t). Overall this suggests they could develop something even more capable once Starship is operational, to ensure the feasibility of their colonization effort. Currently SpaceX possess a top flight development team who require a continuous supply of fresh work, so it seems unlikely they would risk losing this development capability at such a critical juncture.
Version 2 Starship
SpaceX recently began to construct a Version 2 Starship, which will likely become the first fully reusable, Super Heavy Lift (SHL) launch vehicle. Both stages employ the Raptor 2 engine, arguably the best methalox rocket engine in the world. However, SpaceX are continually improving the technology they produce, including their vehicles and engines.
“Raptor 2 has significant improvements in every way, but a complete design overhaul is necessary for the engine that can actually make life multiplanetary. It won’t be called Raptor.” ~ Elon Musk
This could be interpreted to mean SpaceX intend to continue iteration of their Raptor engine to provide the necessary performance for a practical colonization vehicle. Alternately they could plan to produce a new and more powerful engine to replace the Raptor series entirely. Given how engine performance largely determines a launch vehicles capabilities, an examination of what’s physically required to achieve colonization might be the best way to determine their intent.
Any practical attempt at space colonization, such as establishing a permanent settlement on Mars, will likely require bulk transport of unprecedented scale. Currently SpaceX plan to achieve this by launching 1,000 Starship spacecraft to Mars during the month long Mars launch window (which occurs once every 26 months).
“Building 100 Starships/year gets to 1000 in 10 years or 100 megatons/year [to orbit] or maybe around 100k people per Earth-Mars orbital sync.” ~ Elon Musk
This large fleet of Starships would probably require an additional 1,000 propellant depots to refuel them in orbit, before they depart during the relatively short Mars departure window. Fortunately SpaceX would have 25 months to refill these depots between Mars windows, which will probably require 8,000 launches of their Starship Tanker vehicles. Fortunately these vehicles are designed to be rapidly reusable, which suggests only 20-30 Tankers are actually needed to fully replenish these orbital depots over the interim 25 month period. Overall the original plan provides reasonable redundancy during the early stages of the colonization effort as they ramp-up the number of Starships in operation, but scaling to the 1,000 ship level could prove challenging, for a variety of reasons.
The following bar graph illustrates the number of Starship launches to Earth orbit, during the 26 months between Mars launch windows, excluding any launches required to deploy the orbital propellant depots. Assumes each Tanker Starship can transport 150 tonnes of propellant to orbit (due to reduced dry mass), all Mars bound Starships require 1,200 tonnes of propellant and all Crew Starships are launched during the final month. Maintaining passengers in orbit for any longer would expose them to unnecessary risks, such as: radiation exposure, muscle/bone wastage, and deplete valuable resources required for their Mars voyage (e.g. air, food, water etc). Perhaps a delay of a week or two might be acceptable to prove how each Crew Starship performs in space, any further delay is probably not worth the cost.
Overall the advanced capabilities of Starship (100mt to LEO with full reuse, low operating cost, accelerated production etc.) seem the perfect fit for Mars colonization, except when you consider the practicalities of making life multiplanetary. The equipment and personnel required to elevate Mars to a position where it becomes self-sufficient would be staggering, even if they employ bio-engineering and additive manufacturing to produce goods and machinery in situ on Mars. Unfortunately the fleet which plies between Earth and Mars would also have to accommodate normal commerce, e.g. commodities, luxuries and visitors, in addition to essential colony building materials and personnel. Hence even this ambitious 1,000 ship plan could soon become lacking, due to the ever escalating demand for transport, and difficulty operating such a preponderous number of vehicles. In effect SpaceX will have outgrown Starship.
Given all the above, there’s no substitute for scale, hence SpaceX plans to substantially increase their vehicles’ launch capability, through developing a new and more powerful engine called Raptor 3. Of course in the long-term, there’s certainly some latitude in their approach to scale and nuance within each approach…
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