Fuel Duct Question

[Rusty6899]

Basically, I'm trying to perform a return trip to Duna using a 4 stage rocket. I have satellites set up orbiting both Duna and Kerbin for refueling.

My first stage uses serial staging with 7 Jumbo-64's. Second stage uses asparagus staging with 7 Jumbo-64's. Third uses asparagus staging with 7 FL-T800's. Fourth stage (return stage) uses asparagus staging with 7 FL-T400's.

To get into Kerbin orbit takes up the first two stages and the first 2 tanks of my third stage. The problem is that I would rather use serial staging for my third stage before I dock with my Kerbin Space Station and then use asparagus staging after to get a Duna encounter. This would allow me to retain all 7 tanks of my third stage until after I refuel, making my trip to Duna much more feasible.

My question is whether it is possible to disable the fuel ducts during my ascent and then enabling them once I have refueled. I can't see any way of doing it, but if there is I would be happy to hear it.

I realise that I could just not jettison the tanks until after I dock, but then I would miss out on engine power that should really be usable.

[enki]

I would hang on to the tanks until you dock and not worry about it. Would you rather miss out on a little power during the circularization burn or miss out on having that fuel once you get your mission underway? The only good toggle I can think of involves using docking ports to toggle fuel crossfeed and would only add mass and complexity to the craft. If you used TAC Fuel Balancer it will override the fuel lines allowing you to balance the tanks, but still then you'll just have fractions of 7 tanks that are extra weight. You really don't benefit from changing it that I can see.

[CorruptDB]

You can stop fuel flow out of individual tanks by right clicking the tank and clicking the little green arrow next to the fuel/oxidizer amount. It should change into a red circle with a line and shouldn't feed fuel until you re-enable it. As far as I know, you don't have any control over fuel lines themselves.

[Rusty6899]

Well I managed to get there and back anyway. I was pretty close to running out of fuel on the way back. Cheers.