On the evening of April 9, Delta IV Heavy completed its last mission and ended its 20-year flight career as the ULA heavy launch vehicle launched a classified military satellite for the U.S. National Reconnaissance Office.
This launch marks the end of the Delta series rocket’s history — in the future, their work will be taken over by Falcon and Vulcan. In total, the Delta family of rockets, consisting of five different types of boosters, has been launched 45 times in 22 years of operation.
As for Delta IV Heavy, which belongs to the heavy class of rockets and was manufactured by the American ULA, it is actually the third largest payload among current launch vehicles. Like other Deltas, Delta IV Heavy is a development of the United Launch Alliance (ULA), a joint venture between Lockheed Martin and Boeing. The first launch of Delta IV Heavy took place in 2004 and was partially successful due to the off-target orbit of the satellites.
The Delta IV Heavy rocket consists of two stages and two liquid side boosters, as well as two versions of the main fairing. All engines run on a fuel vapor «liquid oxygen — liquid hydrogen». The booster is capable of delivering payloads weighing up to 13.8 tons to geostationary transfer orbit and up to 28.3 tons to low Earth orbit. By April 9, the rocket had been launched 15 times — the main customers were the US National Military Space Intelligence Agency and the US Space Force, but the flight list also includes several non-military missions, including first unmanned spacecraft flight «Orion» and launching into space solar probe «Parker».
The launch was initially scheduled for March 28, but was postponed twice, first due to weather and then due to a malfunction of a pump on the nitrogen gas supply pipeline. The launch of Delta IV Heavy as part of the NROL-70 mission on April 9 was the sixteenth in a row — the rocket took off at 19:53 Kyiv time from the SLC-37B pad at Cape Canaveral Air Force Station. All details of the NROL-70 mission are classified. Most likely, the payload is an electronic intelligence satellite that was sent into geostationary orbit.
It is worth remembering that a few months earlier, the European Ariane 5, which had been flying for 27 years, retired, and its replacement Ariane 6 is late due to a number of technological problems amid a general crisis in European rocketry.