Rocket modules appear for rockets out on missions. I have two rockets out on missions and the cargo bay and liquid oxidizer tanks appeared but I could not interact with them.
Generally rockets have been very buggy recently. For the longest time the rocket on the right had no bars/meters to indicate how full the tanks are; and the rocket on the left would leave those meters after a launch. This is the first time the entire module appears and is persistent through a save game:
I saved a game with two rockets out on missions. When I loaded the game, rocket modules appeared and I could not interact with them.