"Delta IV Heavy: The End of an Era in Spaceflight"

United Launch Alliance's final Delta IV Heavy rocket, the world's most expensive commercially produced rocket, is set to lift off from Cape Canaveral Space Force Station with a classified payload for the National Reconnaissance Office. The rocket, powered by liquid hydrogen, has been a cornerstone for the US military's space program for over 20 years but is being retired to make way for the less expensive and higher-performance Vulcan rocket. The Delta IV Heavy's unique hydrogen-fueled engines create a dramatic fireball during launch, and its legacy includes launching national security missions and NASA spacecraft.