UM…: ULA’s last six Atlas Vs can’t launch anything besides Boeing’s Starliner.

There are six more Atlas Vs in ULA’s inventory to launch Boeing’s Starliner crew capsules to the International Space Station (ISS) under contract to NASA. But it is not certain today that Boeing will use all six of those Atlas Vs. Last year, NASA reduced the number of guaranteed missions in Boeing’s commercial crew contract from six to four after chronic delays in the program. The next Starliner flight will haul cargo to the ISS, expending one of the remaining Atlas Vs.

So what happens to the Atlas Vs left in ULA’s inventory if Boeing doesn’t need to use them all? One idea would be to repurpose the rockets for other missions, perhaps to add launch capacity for the Amazon Leo network. But there’s a catch.

The Starliner spacecraft flies in an exposed configuration during launch, meaning the launch last week was the last time an Atlas V will fly with a payload fairing. Even if Boeing gave up some of the Atlas Vs under its contractual control, ULA would not be able to easily retrofit any of the leftover Atlas Vs for other missions.

A ULA spokesperson confirmed to Ars that the payload fairing now in production for the company’s newer Vulcan rocket—the replacement for the Atlas V—is “not interchangeable” with the out-of-production Atlas fairing.

If — when? — NASA ditches Starliner, it has to be cheaper and smarter to fabricate new fairings than throw away a handful of perfectly good Atlas rockets, right?