the delta-V for the craft will be set to zero when you dock it with another craft in the example shown the crafts have a combined hydrogen mass of 150 tons and I can burn with the engine but the delta-V calculation is showing 0. https://imgur.com/8IPXxpv Here you can see the same main body with a liquid stage docked to it and it is showing a delta-V of zero. https://imgur.com/nMybQyz