The detective work into the Atlas 5 rocket’s first stage performance trouble during the Cygnus cargo ship launch a week ago has implicated the fuel system as the likely culprit for using up the liquid oxygen supply too quickly.

A United Launch Alliance Delta 4-Heavy rocket stands 233 feet tall at Space Launch Complex-6 at Vandenberg Air Force Base, California, ready for liftoff Saturday night carrying a top secret U.S. government spy satellite into orbit.

United Launch Alliance vows a “seamless” switch from the Atlas 5 to the new Vulcan rocket in launches of Boeing’s astronaut taxis.