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United Launch Alliance’s first Vulcan Centaur rocket completed a critical test-firing of its Blue Origin-built BE-4 main engines Wednesday night, clearing one of two remaining technical hurdles before the launcher is cleared for its inaugural flight later this year.

United Launch Alliance called off a test-firing of the company’s first flight-rated Vulcan Centaur rocket at Cape Canaveral Thursday to troubleshoot a problem with the booster’s engine ignition system.

United Launch Alliance’s first Vulcan rocket was filled with methane and liquid oxygen propellants at Cape Canaveral last week for a tanking test, but managers decided to move the rocket back inside a hangar for a few adjustments before proceeding with an engine test-firing.