As SpaceX continues to path find on Starship development and we can expect the production Starship to have different specifications and capabilities than these early versions.
There have already been discussions about its successor and what features should be included in the final production versions.
Starship 2023 & Stretch Starship: Tale of the tape
Future standard Starship models
The specifications of production Starships are likely to be in flux as the vehicle evolves.
Elongating the frame to make more room for propellent and adding more thrust before reaching production stage would seem inevitable for most future Starship variants.
Nine Raptors and Phat Tanks
On December 17th, 2021 the CEO revealed the plans, confirming a tweet published three months prior stating that Starship was “begging for an extra 3 engines.” Musk was likely referring to the fact that a 9-engine Starship – combined with upcoming 33-engine Super Heavy boosters – would create a rocket with 42 engines, a number made famous as “the answer to the ultimate question of life [and everything]” in Hitchhiker’s Guide to the Galaxy – both of which the CEO vocally enjoys.
As ever, it’s thus almost impossible to tell jokes from serious, consequential plans – as is the case with Starship.
Nonetheless, origination aside, adding another three Raptor engines to Starship – boosting the count from six to nine – and stretching its tanks could be a substantial upgrade.
According to amateur modelers, who are generally able to estimate rocket performance with enough information about its structures, shape, and engines; an optimal nine-engine Starship’s tanks would be stretched about 25% to store an additional 300 tons (650,000 lb.) of cryogenic liquid oxygen and methane (LOX/LCH4).
Nine Raptor Orbital Starship- 3 sea level and 6 vacuum
That upgraded Starship would have a liftoff mass close to 1600 tons (3.5M lb) and stand about 55 meters (~180 ft) tall – 10% taller than current ships.
At stage separation, close to vacuum, a stretched Starship with three sea-level-optimized Raptors (RCs) and six vacuum-optimized Raptors (RVacs) should produce at least 2000 tons (4.4M lbf) of thrust – and possibly more than 2250 tons (~5M lbf) depending on engine performance.
At that upper level of thrust, Starship – an upper stage – would be just 10% less powerful than the first stage of Falcon Heavy, the most powerful operational rocket in the world.
Regardless of its thrust, dimensions, or weight, what matters most is how a stretched, nine-engine Starship would impact that overall rocket’s launch performance.
If unofficial modelers are to be believed, the results are significant: compared to a ‘normal’ Starship with a six-engine upper stage and 33-engine booster, the stretched ship could theoretically boost the amount of payload the rocket can launch to low Earth orbit (LEO) from about 150 tons to 220 tons or more (330,000 to 485,000+ lb) – an almost 50% improvement.
In fact, per another recent comment from Musk indicating that Starship – unlike almost all other rockets – won’t temporarily throttle down on ascent, the total payload performance could be a bit less than 230 tons (~500,000 lb) – more than 50% greater than a shorter six-engine Starship.
If those estimates are accurate, upgrading Starship with nine Raptors and stretching its tanks is a no-brainer.
It might slow development and make all nine-engine ships cost a substantial fraction more but a 50% improvement in payload performance would significantly improve the efficiency of Starship’s more ambitious Moon and Mars launch profiles, which require numerous orbital refuelings.