- Having >60% fewer gimbaling engines also means a corresponding reduction in power needed for TVC - so less battery weight.

- additional helium capacity to start the additional engines: thank you - another plus for the new design: LESS helium will be needed onboard, as all fixed engines are only ground-lit -- and fewer engines will be re-lighted in this design.

If it works now why change it?

If the tanker variant is indeed mass not volume limited then how many more engines would it take to change that? Ignoring engine thrust upgrades and the unknown added mass in fuel lines etc for a first approximation.

Quote from: Okie_Steve on 11/27/2023 08:20 pmIf the tanker variant is indeed mass not volume limited then how many more engines would it take to change that? Ignoring engine thrust upgrades and the unknown added mass in fuel lines etc for a first approximation.Rough estimate follows.Assumptions: SuperHeavy dry mass: 200 tonne SuperHeavy propellant capacity: 3400 tonne Ship dry mass: 100 tonne Normal ship propellant capacity: 1200 tonne Normal Starship payload capacity: 100 tonne Bulk density of subcooled methalox: 900 gram/litre Cargo ("nosecone") volume: 1000 m^{3}A fully loaded ship would thus mass 1400 tonne, and the full Starship stack is 5000 tonne. (By "normal" Starship, I mean one that is designed to carry e.g. satellites to orbit, or cargo to the Moon or Mars, i.e. not a tanker or a depot.)Making a tanker by extending the tanks of the ship fully into the nose cone would increase its propellant capacity by 1000m³ * 900g/l = 900 tonne. The ship's mass would then be 100t+1200t+900t = 2200t, and the entire stack's mass would be 200t+3400t+100t+1200t+900t = 5800t.5800t is a 16% increase over 5000t. This actually matches fairly well with the 18% increase in thrust you would get be going from 33 to 39 engines on SuperHeavy.For the ship, 2200t is a 57% increase over 1400t. That's reasonably close to the increase in thrust you get by going from six engines to nine, which SpaceX is already planning.

Making a tanker by extending the tanks of the ship fully into the nose cone would increase its propellant capacity by 1000m³ * 900g/l = 900 tonne. The ship's mass would then be 100t+1200t+900t = 2200t, and the entire stack's mass would be 200t+3400t+100t+1200t+900t = 5800t.

Quote from: Okie_Steve on 11/27/2023 08:20 pmMaking a tanker by extending the tanks of the ship fully into the nose cone would increase its propellant capacity by 1000m³ * 900g/l = 900 tonne. The ship's mass would then be 100t+1200t+900t = 2200t, and the entire stack's mass would be 200t+3400t+100t+1200t+900t = 5800t.Did you notice what you just wrote? by adding 6 more engines - no other improvements included - the tanker's performance jumped 10x from 100t to 1,000t (!!) I am sure this is overly optimistic, but it does get the point across well: this proposed configuration may be really useful.

I mean SH used to have 37 engines, so I don't think an increase of engine count from the current 33 is out of question. But I imagine it's a pretty low priority right now.