Powerful Delta IV Heavy rocket launches US spy satellite

The powerful United Launch Alliance (ULA) rocket launched a hush-hush satellite for the US National Reconnaissance Office (NRO) from Vandenberg Space Force Base in California on September 24.

The Delta IV Heavy took flight at 6:25 p.m. EDT (2225 GMT; 3:25 p.m. local time) from Vandenberg's Space Launch Complex-6 on a mission called NROL-91, Space.Com reports.

The NRO builds and operates the US fleet of spy satellites, the activities and payloads of which tend to be classified.

An NRO mission description(opens in new tab) outlines NROL-91 only in vague terms, saying it "supports the overall national security mission to provide intelligence data to the United States' senior policymakers, the Intelligence Community and Department of Defense".

This launch was the 14th overall for the Delta IV Heavy, which debuted in 2004. The 233-foot-tall (71 metres) rocket is capable of lofting 62,540 pounds (28,370 kilograms) to low Earth orbit (LEO), more than any other currently operational launcher except SpaceX's Falcon Heavy.

ULA is phasing out the Delta IV Heavy in favour of a new rocket called the Vulcan Centaur, which could debut by the end of 2022. Just two Delta IV Heavy flights remain, both NRO missions that will launch from Cape Canaveral Space Force Station in Florida. Those missions will lift off in 2023 and 2024 if all goes according to plan.