As United Launch Alliance (ULA) counts down to the planned 9 a.m. EDT Thursday launch of its final Delta IV Medium booster, this week offers an opportune moment to reflect on the career of a vehicle which has delivered a smorgasbord of military, civilian and scientific payloads into Earth orbit and beyond over the course of a spectacular 17-year career.
And although the Medium’s big brother—the Delta IV Heavy—will remain operational, in the words of ULA, “as long as it is required by our customers”, the swansong of this familiar orange-and-white rocket brings the curtain down on an impressive 100-percent mission success rate. In spite of an upper-stage anomaly experienced back in October 2012, the Delta IV has never failed to deliver its primary payload to the correct orbit.
On the eve of its final flight, the Delta IV Medium has flown 28 times from either Space Launch Complex (SLC)-37B at Cape Canaveral Air Force Station, Fla., or Space Launch Complex (SLC)-6 at Vandenberg Air Force Base, Calif. Its 29th and final mission on Thursday will see it deliver the second member of the Global Positioning System (GPS) Block III constellation of positioning, navigation and timing satellites into orbit. In the end, the prohibitively high costs of the “single-stick” Delta IV product line conspired heavily in hastening its retirement.