I assembled a large and relatively modular ship in orbit recently for the purpose of interplanetary travel. I wanted to attach a nuclear engine to the bottom of the ship for more efficient long-range thrust however it seems that It isn't drawing fuel properly. It is attached using a few sets of decouplers and a few service bays and a few hitchhiker cans lie between the engine and the tanks. I make this configuration on the ground and it works just fine but no matter what I try in space it won't fire or even recognizes the fuel being attached to the engine. The only real difference between the ground config and the space one is that the space one was assembled in space and the ground one being assembled in the VAB. Here is a picture, any ideas?