I don't think we really have a proper equivalent for that. Though I guess what's left to explore is mostly deep ocean and we're not really expecting to need much in the way of diplomacy down there. Then again, we have made first contact with aliens, so some kind of global diplomatic representation might be a good idea, but it seems pretty unlikely with the world as it is. More likely America will just muscle its way in and take over by virtue of having the most advanced space program.