What's the technical term for that kind of positive feedback?
In general engineering, "the Scaling Problem." That occurs when the algebraic relationship between the requirement and the provision is not linear (e.g., doubling the volume of a tank requires four times the mass of the tank structure), or also when various properties of a single solution do not scale harmoniously (e.g., yield strength versus length versus mass of a beam). The way it works for rockets is particularly insidious.
But a very useful measure is the simple mass ratio. That's the ratio of a vehicle's total mass to its dry mass -- i.e., the mass that isn't fuel. A vehicle that masses 10,000 kg fully loaded, but whose structure, equipment, and crew mass only 2,000 kg has a mass ratio of 5. The mass ratio and the specific impulse of the propulsion system give the vehicle's overall ability to change its velocity, and holds as the absolute masses change while preserving the mass ratio.
But of course that masks the aspects of vehicle structural design that you alluded to. The mass ratio of a typical Earth launch booster these days is around 20. The mass ratio of the lunar module (2,200 kg dry mass, 2,400 kg ascent fuel) is about 2.1. That's the magic figure. Fuel reserved for the TEI burn would be considered part of the dry mass of the lunar module von Braun initially had in mind and thus significantly increase the ascent fuel requirement. That's the genius of the LOR approach. It's risky in the sense that it requires a lunar orbit rendezvous maneuver, but it's advantageous in that it requires considerably less fuel than von Braun's original estimate and assumptions.
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