Gary Zhou 
United Launch Alliance is targeting the launch of the penultimate Delta IV Heavy with the secretive NROL-68 mission at 3:29 AM ET (07:29 UTC). The launch will take place from Space Launch Complex-37 located at Cape Canaveral Space Force Station in Florida.
The Delta IV Heavy was first stacked at Space Launch Complex-37 back in early 2023 and originally targeted to launch mid-April 2023, however, an undisclosed issue came up during pre-launch checkouts forcing a delay to now.
The 33-story Mobile Service Tower that provides access and is currently shielding the rocket from Florida’s weather is due to be rolled back this evening ahead of launch, the tower is raised just a few inches by 40 hydraulic cylinders and rolls back at 0.25 mph to a safe point ~100 yards away. This could be delayed though by afternoon thunderstorms, but the launch window extends until 7:45 AM ET (11:45 UTC).
The Delta IV Heavy consists of 3 core boosters, each with an RS-68A engine. The hydrogen-fueled rocket produces 2.1 million lbs of thrust at liftoff, which can launch up to 62,540 lbs (28,370 kg) to low Earth orbit.
Following lift-off, the booster will head on an Easterly trajectory over the Atlantic Ocean, about 2 and a half minutes into the flight, the 2 side boosters are expected to separate 2 and a half minutes into flight according to ULA’s visibility map, however during past NRO launches, this has been just a vague placement due to the secrecy of the payload. Payload fairing separation will occur approximately 7 minutes into the flight and will also signal the end of ULA’s launch live stream at the request of the National Reconnaissance Office.
Launch weather at lift-off is predicted to be 75% favorable, but ULA will be monitoring lingering thunderstorms and high-ground winds. If weather or technical issues do not allow for launch, there are 2 opportunities for 24 and 48 hours later.
Watch the launch here, especially the lift-off as the Delta IV Heavy lights its engines.
