Where should teams draw the line between mission, epic, voyage, and story?

[rupurt]

One of Keel's strongest opinions is that the hierarchy should mean something.

Where do you personally draw the line between:

• mission as objective
• epic as problem space
• voyage as planned campaign
• story as executable slice

What anti-patterns have you seen?

• stories that should have been voyages
• voyages that should have been epics
• missions that are really just large tickets

Concrete examples would be especially useful.