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On its fifth try, a United Launch Alliance Delta IV rocket blasted off from Cape Canaveral at 7:28 p.m. today with three Air Force satellites.

Weather pushed the launch 45 minutes into a 65-minute window, but the rocket finally jumped from its pad with 821,000 pounds of thrust and sailed into a mostly clear blue sky. Sunlight caught the rocket's contrail as it arced southeast over the Atlantic and cast shadows on clouds below.

The 27th flight of a Delta IV appeared to be off to a good start, but at the Air Force's request ULA cut off its broadcast about five minutes into the flight, after the upper stage engine ignited.

It could be several hours before ULA confirms the launch was a success.

The primary mission aboard the 20-story Delta IV was the Air Force's first two of four satellites that will patrol near-geosynchronous orbits, roughly 22,000 miles above the equator, for threats to U.S. spacecraft.

Many high-value military and commercial satellites orbit in that region, and the Air Force is increasingly concerned about an attack on one of them. As a deterrent, the Air Force declassified the existance of the Geosynchronous Space Situational Awareness Program (GSSAP) earlier this year.

The satellites will circle around the geosynchronous belt and inspect other spacecraft up there to better understand their capabilities. They would see if any satellite got too close to U.S. vehicles.

Also on board the rocket was a small experimental satellite called ANGELS, developed by the Air Force Researach Laboratory. The satellite was designed to practice close approaches of the rocket's spent upper stage, testing technologies that could further improve the military's ability to autonomously approach and inspect other high-orbiting spacecraft.

While the GSSAP and ANGELS capabilities are intended to protect U.S. satellites, some countries may be concerned about their potential to be used for aggressive acts.

If this flight goes smoothly, ULA plans to follow up with a second launch this week from the Cape. An Atlas V is targeting an 11:23 p.m. liftoff with a new GPS satellite, at the opening of an 18-minute window.

SpaceX is preparing a commercial satellite for launch on a Falcon 9 rocket early Aug. 4, potentially resulting in three Cape launches in one week.

Today's mission was a struggle to get off the ground. Technical trouble scrubbed the first attempt last Wednesday, and then weather spoiled three more countdowns on consecutive days.

Today's forecast called for a 60 percent chance of favorable weather, and the odds finally came out in the Delta IV's favor, with 20 minutes to spare in the window.

With this launch complete, ULA plans to perform some modifications to Launch Complex 37 to support the planned first flight of NASA's Orion exploration capsule in December.

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