Last night I got the cargo screen for ships up and running. It will currently display a sortable list of cargo that is on the ship, and if the ship is landed at a colony owned by the same player, it will also display a list of all cargo assigned to that colony.
Now I need to add the functionality that will let the player transfer cargo between the ship and the colony, and also to split and merge groups of the same type. This will allow the player to take a 100 unit pile of ore and split it into two piles before transferring one pile to the colony, or vice versa.
Eventually ships will be able to dock to each other and transfer cargo, and expeditionary forces will have the same abilities. All of this is necessary before I can implement the mining, gas giant scooping, and comet harvesting actions in the game since those all create new piles of materials and there has to be some place to put them.