First launch attempt for Delta IV’s final mission gets scrubbed

United Launch Alliance’s Delta IV rocket is set to embark on its final mission, the NROL-70, for the National Reconnaissance Office (NRO). This launch will mark the 45th and last flight of the Delta IV, a rocket that has been in service since November 2002. Delta IV was developed by McDonnell Douglas, which merged with Boeing in 1997. The rocket was designed as a modular system, capable of flying in various configurations depending on the mission requirements. Friday’s mission will utilize the Delta IV Heavy configuration with three common booster cores (CBCs) and a five-meter Delta cryogenic second stage (DCSS).

Delta IV and Atlas V, both developed under the Evolved Expendable Launch Vehicle (EELV) program, were once fierce competitors. However, in 2006, United Launch Alliance (ULA) was formed, combining the satellite launch operations of Lockheed Martin and Boeing into a single organization. ULA has since been responsible for marketing launches to the US government. Delta IV has mainly served US military customers, including the Space Force and the NRO. Its missions have included communication satellites, weather satellites, navigation satellites, space surveillance satellites, and more. Notably, Delta IV Heavy also carried out high-profile missions for NASA, such as the Exploration Flight Test 1 (EFT-1) in 2014 to test the Orion spacecraft and the launch of the Parker Solar Probe in 2018 to study the Sun.

The NROL-70 mission is classified, but public information suggests that it involves launching an electronic signals intelligence satellite destined for geostationary orbit. Geostationary ELINT satellites are part of a series called Orion and are used for intercepting radio signals from terrestrial sources. These signals are then relayed back to the NRO for analysis. This will be the 17th Delta IV launch for the NRO and the seventh time an Orion satellite has been launched aboard a Delta IV.

The final flight of Delta IV has long been anticipated due to ULA’s plans to phase out the rocket and focus on its next-generation Vulcan rocket. Vulcan is expected to take over Delta IV’s responsibilities and fulfill US military launch requirements in the future. With the retirement of Delta IV, ULA will now rely on its Atlas V and Vulcan rockets for future missions.

Friday’s launch is scheduled to take place from Space Launch Complex 37B (SLC-37B) at the Cape Canaveral Space Force Station. SLC-37B was originally built for the Saturn I rocket during the Apollo program. Delta IV has predominantly launched from SLC-37B, with the remaining launches taking place at Vandenberg Space Force Base’s Space Launch Complex 6 (SLC-6). SpaceX will take over SLC-6 for its Falcon 9 and Falcon Heavy rockets.

The Delta IV Heavy rocket used for Friday’s mission has three CBCs and a five-meter DCSS second stage. The countdown will progress with the loading of liquid hydrogen and liquid oxygen propellants into the first and second stages. At liftoff, the engines will ignite, producing a fireball this is common for Delta IV Heavy launches. The rocket will ascend on an easterly trajectory over the Atlantic Ocean, targeting a geostationary orbit. Shortly after liftoff, it will perform a pitch-and-yaw maneuver to align itself with its planned ascent path. As the boosters approach propellant depletion, they will throttle down to limit acceleration. After shutdown, the outboard boosters will separate from the center core, which will continue burning until booster engine cutoff (BECO). The first and second stages will then separate, and the DCSS will deploy its RL10C-2-1 engine to perform multiple burns to reach geostationary orbit. The payload fairing will be jettisoned, and spacecraft separation will occur, followed by a collision avoidance maneuver to ensure the DCSS does not pose a threat to operational satellites.

After Friday’s launch, Delta IV’s long history will come to an end. The name “Delta” dates back to the early days of the US space program and has evolved over time with different versions and configurations. Delta IV’s retirement leaves ULA with the Atlas V and Vulcan rockets to fulfill future launch requirements. Vulcan made its maiden flight in January and has been selected, along with SpaceX’s Falcon 9 and Falcon Heavy, for future US military launches under the National Security Space Launch program.