When you say refueling missions I assume you mean Starship tankers that will refuel Starship in orbit. Actually they will be perhaps a slightly shorter version of Starship but they will have to carry extra fuel as a payload. That means either their tanks are bigger or they have special tanks just for refueling Starship. They won’t have a crew compartment or a place for a payload. Their payload is the extra fuel.
It is possible it will look something like this, shorter because propellant is much more dense that any payload or crew area. It is also possible they will actually have 4 tanks instead of 2 larger ones. That could mean special tanks just for the extra fuel with unique plumbing to make it easier to transfer the propellant. If it were 4 tanks I think it would be a bulkhead in stead of a dome on top of the methane tank with shorter LOX and methane tanks and then finally a dome on top of the upper methane tank.
The reason I suggest that alternative is that to transfer propellant out of a standard Starship tank you pump it out the bottom, the same way you load it and how it feeds the engines. In order to do that you have to provide settling thrusters that push both ships in the forward direction. That is the only way to be sure the propellent is at the outlet, allowing you to pump it. That settling thrust uses about 5% of the fuel brought by the first tanker but as the mass grows that rises to somewhere around 15% of the fuel used up thrusting.
The 4 tank alternative could allow for very unique plumbing in the upper smaller tanks where the outlet is on the tile side of the tank but is piped through the tank to the shinny side where it is fed to the Starship using a pump. That would allow simply spinning the ships for the settling gravity and saves almost all of that wasted fuel, which adds up to about 1 tanker worth for a full load like a moon mission.
This image is off a little. The half toward each other should be shiny stainless steel, but this is how the tanker will mate to Starship for propellant transfer, though it might even be inverted. That way if it has the smaller forward tanks the lines could interface directly with Starship’s fill lines without running the length of the ship. Those fill lines are near the engines.
