Last West Coast Delta IV Heavy to launch with NROL-91 - NASASpaceFlight.com - NASASpaceflight.com

United Launch Alliance’s (ULA) Delta IV Heavy rocket made its last West Coast launch on Saturday, carrying out a mission for the National Reconnaissance Office, as it moves one flight closer to retirement.

Liftoff of the NRO Launch 91 (NROL-91) mission from Space Launch Complex 6 — at the Vandenberg Space Force Base in California — took place at 3:25 PM PDT (22:25 UTC).

Delta IV Heavy is the most powerful version of the Delta IV, one of two rockets developed under the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program to meet the US Government’s launch needs in the early 21st century.

One of the first steps in that transition was winding down Delta IV operations, with the last Delta IV Medium+ launch taking place in 2019.

Delta IV Heavy, with its significantly higher payload capacity, has been kept in service to carry out a handful of national security launches that cannot be performed by Atlas V.

Saturday’s mission, NROL-91, is the final Delta IV launch from California’s Vandenberg Space Force Base, with the rocket’s remaining missions to be executed from the East Coast at Cape Canaveral.

While the National Reconnaissance Office (NRO) keeps details of its satellites classified, the use of a Delta IV Heavy and the fact the launch is taking place from Vandenberg speak volumes.

Delta IV Heavy missions carry satellites that have too great a mass for the most powerful Atlas V configurations to place into their destined orbits, indicating the satellite is very heavy, bound for a high orbit, or both.

Those signals intelligence satellites are typically launched by smaller rockets, so the combination of rocket and launch site suggests that NROL-91 will deploy one of the agency’s large imaging satellites, part of a program identified in previously leaked documents as Crystal.

The satellite launched by the NROL-91 mission is expected to take on the designation USA-337, the next available number in this sequence.

Deployed by the NROL-71 mission in January 2019, it was the last-but-one KH-11 to launch prior to NROL-91.

Hazard areas published ahead of the NROL-91 mission, to warn aviators and mariners to stay away from areas where debris from the launch is expected to fall, suggest that this mission is targeting the same inclination as USA-290, rather than the more typical SSO

With Saturday’s launch marking the last Delta IV flight from Vandenberg, it is not clear whether this also means that NROL-91 was the final launch of a Crystal satellite

Future missions could follow this model, or alternatively, Crystal satellites could continue launching aboard a different rocket — such as Falcon Heavy or ULA’s next-generation vehicle, Vulcan

Delta IV during rollout from the Horizontal Integration Facility to the launch pad ahead of the NROL-91 mission (Credit: United Launch Alliance)

The Delta IV Heavy is a two-stage expendable launch vehicle, with its first stage consisting of three Common Booster Cores (CBCs)

First flown in November 2002, Delta IV has made 42 flights prior to the NROL-91 mission, of which 13 have used the Heavy configuration

The NROL-91 payload, encapsulated in its fairing, is installed atop the rocket (Credit: United Launch Alliance)

Although the Delta IV program is being wound down, Saturday’s launch marks the first flight of a new engine variant, the RL10C-2-1, which replaces the RL10B-2 used on previous Delta IV missions

The RL10C-2-1 is expected to be used on the remaining Delta IV launches, as well as future Space Launch System (SLS) missions with the Interim Cryogenic Propulsion Stage (ICPS), which is derived from DCSS

Delta IV launches from Vandenberg Space Force Base take place from Space Launch Complex 6 (SLC-6), and with Saturday’s launch marking the last Delta IV mission from Vandenberg, this is expected to be the last time the complex is used in its current configuration

After MOL’s cancellation, SLC-6 was selected as a launch site for Space Shuttle missions to polar orbit

Such orbits could not safely be reached from the Kennedy Space Center, so a launch pad on the West Coast was deemed necessary for planned military Shuttle missions

Athena was far smaller than the rockets that SLC-6 had been designed to serve, but Boeing’s need to find a West Coast launch site for its Delta IV rocket would bring the pad a new lease of life

The first of 10 Delta IV flights from the pad — including the NROL-91 mission — took place in June 2006 when a Delta IV Medium+(4,2) flew the NROL-22 mission, deploying a signals intelligence satellite

Including Saturday’s launch, the Delta IV Heavy configuration has used the pad five times, with all of its launches deploying Crystal satellites

Overall, NROL-91 is the fourteenth launch to take place from SLC-6

In keeping with previous Delta IV missions, the rocket has been assigned a flight number, or Delta number, which indicates its place in the history of the Delta series of rockets

While the Delta IV is a completely different rocket even compared to the Delta II that retired a few years ago, the tradition has been maintained, and the rocket that performed Saturday’s launch is be Delta 387

10 seconds into the burn, Delta IV’s payload fairing separates, and the NROL-91 payload is exposed to space for the first time

With Delta 387’s mission complete, only two more Delta IV missions remain to be launched

This is one of three Atlas V launches currently slated for the tail end of 2022, with deployment of JPSS-2, a military weather satellite, slated for the start of November and the US Space Force 51 (USSF-51) mission tracking no earlier than December

(Lead photo: Delta IV Heavy and NROL-91 ascend toward orbit. Credit: Jack Beyer for NSF)