United Launch Alliance (ULA) has called off Thursday's (Mar. 28) attempt to launch its final Delta IV Heavy rocket, which was supposed to carry a US spy satellite from Cape Canaveral Space Force Station in Florida.

According to a ULA statement obtained by Space.com, the attempt was scrubbed with just under four minutes left in the countdown "due to an issue with the gaseous nitrogen pipeline which provides pneumatic pressure to the launch vehicle systems."

The next attempt was planned for Friday, Mar. 29, at 13:37 ET (17:37 UTC).

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The Delta IV Heavy carrying a classified payload for the National Reconnaissance Office (NRO) would be the 16th and final mission for the rocket configuration and the last for the Delta rocket family, which has been flying for over six decades. It would be replaced by the Vulcan Centaur, which made its maiden flight earlier this year carrying Astrobotic's ill-fated Peregrine moon lander.

The NRO builds and operates the US's fleet of spy satellites and rarely divulges many details about their launch capabilities.

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