File image of the Atlas 5 rocket sitting at the launch pad. Photo: Lockheed Martin

The debut launch of Lockheed Martin's next-generation Atlas 5 rocket has been officially rescheduled for August 12 following the successful completion of some additional umbilical retraction tests.

Liftoff from Complex 41 at Cape Canaveral Air Force Station in Florida will occur around 6 p.m. EDT (2200 GMT). The exact launch window will be computed 30 days in advance.

Managers decided to delay the July 29 target launch date so engineers could repeat a full checkout of the umbilical retraction system, which pulls back the various lines running from the mobile launching platform to the rocket at liftoff, a Lockheed Martin spokeswoman explained.

In an earlier test, engineers didn't like how one umbilical retracted. Subsequent efforts got that line to work properly. But Lockheed Martin opted to delay the launch in order to test the retraction of the entire umbilical system one more time to ensure there will be no problems when the Atlas 5 blasts off, the spokeswoman said.

The August 12 launch date was selected since it was the next available slot on the Air Force-controlled Eastern Range, according to Lockheed Martin.

The Atlas 5 will be rolled atop the mobile platform from the Vertical Integration Facility to the open-air launch pad on July 15 for the third and final countdown dress rehearsal before its maiden voyage. Events during this test will occur at virtually the same time of day they will during the real countdown, providing a realistic simulation.

The rocket will be fully fueled as the countdown reaches the final moments on July 16, giving the launch team another chance to practice procedures. This rehearsal, however, will be the first time mission customer Eutelsat will be on hand. The company's Hot Bird 6 direct-to-home TV broadcasting satellite will be launched by this inaugural Atlas 5.

If all goes well, the rocket will be safed and rolled back to the Vertical Integration Facility on July 17.