ULA/Jeff Spotts

After Saturday night’s successful delivery of an Air Force communications satellite to orbit, the medium variant of the Delta IV rocket has now launched 26 times. All of the Delta IV medium launches, which primarily have served the US armed forces, have ended in mission success.

Other US-based rockets have launched more, but no modern rocket with all-American components, from the engines and solid-rocket motors to the upper stage, can boast of such a record of success as the Delta IV Medium. And yet now the rocket’s parent company, United Launch Alliance, desperately wants to retire the booster. Why?