SpaceX's Falcon rocket family is close on Delta's heels and could surpass the 389-flight milestone later this year. However, there's an important distinction to make with the Delta IV rocket ...

Fiery scenes from a Sept. 24, 2022, liftoff of a Delta IV Heavy rocket. Video by United Launch Alliance The Delta IV Heavy burns ultracold liquid hydrogen, which is a high-performance fuel.

The United Launch Alliance's (ULA) Delta IV Heavy rocket lifted off from Space Launch Complex-37 (SLC-37) at Cape Canaveral Space Force Station in Florida at 12:53 p.m. EDT (1653 GMT) on April 9 ...