![]() How to calculate the Δv of a rocket stage that transitions from Kerbin atmosphere to vacuum.Δv = ln ( 18 Tons / 2 Tons ) × 380 seconds I sp × 9.81m/s² = Maximum Δv of 8199.1632327878 m/s Δv = 2.1972245773 × 380 seconds I sp × 9.82m/s² = Maximum Δv of 8199.1632327878 m/s (Replaced the log of mass with a constant as the ratio of total mass to dry mass is constant regardless of the number of tanks used as there is no other mass involved) Δv = 21.576745349086 × 380 seconds I sp = Maximum Δv of 8199.1632327878 m/s (Reduced to its most simple form by combining all the constants) True Δv The following example will use a single stage and fuel tanks in the T-100 to Jumbo 64 range with an engine that outputs 380 seconds I sp. This calculation only uses the mass of the fuel tanks and so the ln ( Mstart / Mdry ) part of the Δv equation has been replaced by a constant as Mstart / Mdry is always 9 (or worse with some fuel tanks) regardless of how many fuel tanks you use. Δ v = l n ( M s t a r t M d r y ) ⋅ I s p ⋅ 9.81 m s 2
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