This requirement grew out of concerns about SpaceX and how frequently they update the design of Falcon 9. And from where NASA stands, it’s a totally valid concern and requirement. The problem is that it has very blatantly only ever been applied to SpaceX.
The US Air Force has developed a viable corridor for launching to polar and other high-inclination orbits from Cape Canaveral. I spend some time thinking through who may be interested in using that corridor and what its existence could mean for the newer launch vehicles in development.
In thinking through who may launch to high-inclination orbits from the Cape, I totally forgot about DARPA’s XS-1 that will be based out of Cape Canaveral. I would be surprised if there weren’t plans to launch XS-1 from Vandenberg, but as of yet, we haven’t heard anything. Maybe the Department of Defense had XS-1 in mind when developing a polar corridor from Cape Canaveral?
Plans could change, obviously, but the last bit there seems to confirm that Orbital ATK is only going to build this launch vehicle if they are awarded funding from the Air Force in the upcoming Launch Services Agreements.
ZUMA has been wrapped up in the mystery surrounding USA 276 and the ISS since last November, when Marco Langbroek found that its launch window and trajectory lined up very closely to their orbits. After a few delays (with little insight into their causes, much like the launch of USA 276…), things seem to be lining up again.