The National Reconnaissance Office’s (NRO) NROL-91 mission lofted into orbit aboard a United Launch Alliance (ULA) Delta IV Heacy rocket on Sept. 24–the fifth and final Delta IV Heavy launch from Vandenberg Space Force Base, Calif., since 2011.

ULA is a partnership between Lockheed Martin [LMT] and Boeing [BA].

Two ULA Delta IV Heavy launches of NRO payloads from Cape Canaveral Space Force Station, Fla., remain next year and in 2024, the NRO said.

NRO Director Chris Scolese praised the role of Delta IV Heavy and Medium variants in 15 NRO launches since the NROL-22 mission in 2006 and said in a statement that the agency “will explore new vehicles for launching payloads even more efficiently and effectively, with even greater capacity, agility, speed, and resilience.”

The final Delta IV Medium launched from Vandenberg on the NROL-47 mission in 2018, per NRO.

Of late, the agency has stressed that it is pursuing a responsive space strategy with industry to strengthen intelligence, surveillance, and reconnaissance coverage and provide lower cost, domestic and international launches.

In July, the NRO and the Australian Department of Defense launched a jointly developed payload aboard a Rocket Lab USA [RKLB] Electron rocket from Rocket Lab Launch Complex-1 in New Zealand for the NROL-162 mission (Defense Daily, July 13).

In February, NRO launched the NROL-87 mission aboard a SpaceX Falcon 9 rocket–NRO’s first launch this year–followed by the NROL-85 mission in April aboard the reused rocket body from NROL-87–the first rocket reuse by the NRO and the second Falcon 9 launch under the U.S. Space Force’s National Security Space Launch contract.