I suspect it's just a technology demonstrator, and test bed for materials..
...for something related to Prompt Global Strike (pretty decent Wiki page)
In a nutshell, there is a desire within the Pentagon for a conventional warhead equipped weapon, that can strike targets anywhere in the world within one hour, from CONUS, obviating the need ($$$) for Aircraft Carriers, and political headaches of basing tactical aircraft in foreign nations.
Cruise missile platforms, SSN's, surface combatants, (as well as carriers, and land based aircraft) aren't always in the right place, at the right time. And as amazing as cruise missiles are, they are relatively slow and vulnerable.
Not saying I'm all on board, but that is the general idea. (of Prompt Global Strike)