Enlarge / United Launch Alliance's first Vulcan rocket on the launch pad before liftoff in January. (credit: United Launch Alliance)

The second flight of United Launch Alliance's Vulcan rocket will take off in September with a dummy payload in place of Sierra Space's Dream Chaser spaceplane, preserving a chance for ULA to begin launching US military satellites on the new rocket by the end of the year, officials announced Wednesday.

Tory Bruno, ULA's CEO, announced the change in flight plan for the second Vulcan rocket in a conference call with reporters. There was little hope Sierra Space's Dream Chaser would be ready to make its first resupply run to the International Space Station before the end of the summer.

Dream Chaser had been booked to launch on the second test flight of ULA's Vulcan rocket for the last five years. With the near-flawless inaugural flight of Vulcan in January and a successful second flight later this year, ULA's Vulcan will be certified by the US Space Force to loft the military's most sensitive national security satellites into orbit.