NROL-91 liftoff. Credits: ULA

NROL-70 Mission Launches On ULA’s Last Delta IV Heavy Rocket

United Launch Alliance (ULA) has successfully launched its last Delta IV Heavy rocket, carrying the NROL-70 classified mission

On April 9, 2024, after a 20-year-long career, the last Delta IV Heavy rocket lifted off from SLC-37B at Cape Canaveral, Florida. ULA’s most powerful launch vehicle cleared the launch pad for the last time at 16:53 UTC, carrying the NROL-70 mission for the US National Reconnaissance Office (NRO). Nearly four minutes after liftoff the lateral booster separated from the central core, which released the second stage 40 seconds later.

The liftoff was firstly scheduled for March 28. However, the launch was scrubbed due to an issue with a liquid pump failure on the gaseous nitrogen pipeline which provides pneumatic pressure to the launch vehicle systems.

A classified mission

NROL-70 was awarded in 2019 to ULA, as part of the National Security Space Launch (NSSL) phase 2 contract.

Since it’s a mission for a government agency, the payload is classified. So, no details about the purpose, mass, and size of the satellite have been disclosed to the public. ULA has only stated that “the NROL-70 mission will strengthen the NRO’s ability to provide a wide-range of timely intelligence information to national decision makers, warfighters, and intelligence analysts to protect the nation’s vital interests and support humanitarian efforts worldwide.”

NROL-70 poster. Credits: NRO
NROL-70 poster. Credits: NRO

As for previous missions of this type, the live broadcast ended shortly after the separation of the upper stage.

With today’s launch, an important chapter in American aerospace history has closed. For years, the Delta IV Heavy, the heaviest version of the Delta IV family, has been the most powerful rocket in operation worldwide.


An arduous launch history

Initially developed by Boeing, it later came under the management of United Launch Alliance (ULA), a joint venture between Lockheed Martin Space and Boeing established in 2006.

The maiden launch, in December 2004, was a partial failure. An earlier shutdown of the side booster caused an incorrect deployment of the payload. In 2007 it successfully launched the DSP-23 mission, as part of US Space Force’s Defense Support Program. However, since this first successful flight, the Delta IV Heavy only launched 14 more times, with a less-than-exceptional average of fewer than one launch per year.

Among the rare flights of the rocket are mainly missions for the NRO, in addition to the launch of NASA’s Parker Solar Probe and the Exploration Flight Test (EFT-1) of the Orion capsule in 2014.

A Delta IV Heavy liftoff carrying the Orion capsule during EFT-1 mission. Credits: ULA
A Delta IV Heavy liftoff carrying the Orion capsule during EFT-1 mission. Credits: ULA

Over the years, the rocket has faced significant challenges in carving out space in the global market, mainly due to its high costs. The arrival of SpaceX’s Falcon 9 and Falcon Heavy marked a decisive moment, prompting ULA to retire it in anticipation of shifting launches to the company’s new Vulcan rocket. For example, a launch aboard the Delta IV Heavy had a cost of at least $300 million, significantly higher compared to the approximately $100 million per launch of the Falcon Heavy.

The maiden launch of Vulcan Centaur, which will fly 38 times for Project Kuiper. Credits: United Launch Alliance
The maiden launch of Vulcan Centaur. Credits: ULA

This has also led to a diversification in the allocation of contracts for NSSL mission launches. Whereas the Delta IV Heavy was once a primary choice for the DoD, now, for example, the last 21 launches awarded by the Space System Command are almost evenly distributed between ULA and SpaceX.


The rocket in details

The ULA’s Heavy-lift rocket stands 70 meters tall and is capable of carrying up to 28 metric tons of payload to Low Earth Orbit (LEO) and 13 metric tons into geostationary transfer orbit (GTO).

The first stage consists of three common booster cores (CBC) strapped together. Each booster is powered by one RS-68A LH2/LOx engine, capable of producing 3,100 kN of thrust at liftoff. The Delta Cryogenic Second Stage (DCSS) is powered by a single, vacuum-optimized RL10 LH2/LOx engine. Both the first and second stage’s engines were manufactured by Aerojet Rocketdyne.

The iconic fireball during NROL-68 mission liftoff. Credits: ULA
The iconic fireball during NROL-68 mission liftoff. Credits: ULA

Despite the rare flights, launches of the Delta IV Heavy have always been exciting for enthusiasts. Iconic is the characteristic fireball that forms upon engine ignition. At the start-up of the RS-68 engines, for a few seconds only liquid hydrogen is released, which being highly volatile, rapidly propagates upwards along the sides of the rocket. When the oxygen flow also begins in the engines, the excess hydrogen burns rapidly, creating the spectacular flame that engulfs the boosters.

Farewell to the “most metal” of rockets.


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Francesco Sebastiano Moro

Francesco Sebastiano Moro

Aerospace engineering student at University of Padua, passionate of space and aerospace sector.

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