United Launch Alliance Delta 4 Heavy launcher carries NROL-32

A United Launch Alliance Delta 4 Heavy launches with a National Reconnaissance Office payload NROL-32 from Space Launch Complex-37 at 5:58 p.m. EST (2258 GMT). Credit: Pat Corkery/United Launch Alliance

The launch came after the first attempt was scrubbed for 48 hours due to issues suffered during fuelling - relating to anomalous temperature data signatures detected on the port and starboard strap-on common core boosters during cryogenic fueling.

Delta IV-H Preview:
The Delta IV which will perform the launch is Delta 351, a Delta IV Heavy with three Common Booster Cores and an upper stage with a diameter of five metres.

The first stage of the Delta IV is a Common Booster Core or CBC, powered by a single RS-68 engine. This will be augmented early in the flight by two additional CBCs attached to it on either side.

The second stage is the five metre Delta Cryogenic Second Stage or DCSS, which is powered by one RL10-B-2 engine.

More about NRO at NASA Spaceflight