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When the countdown clock reaches zero, the Atlas V booster engine and single solid rocket booster ignite and the flight begins. The vehicle reaches Mach 1 after about 57 seconds, then flies through "Max Q," the area of maximum aerodynamic pressure, about 12 seconds later. The rocket's single solid rocket booster will be jettisoned after …

The countdown has resumed and there are four minutes remaining until the 7:05 p.m. liftoff of the United Launch Alliance Atlas V rocket carrying NASA's OSIRIS-REx spacecraft.

The switch to internal power is complete. Standing by to pick up the countdown at 7:01 p.m.

Launch Conductor Scott Barney has checked in with his ULA team members and they confirmed they are go to resume the countdown at the T-4 minute mark. The hold will be released at 7:01 p.m. Liftoff is on schedule for 7:05 p.m. EDT.

OSIRIS-REx is switching from ground-based to internal power.

Countdown clocks are holding for 15 minutes in the final built-in hold of the night.

Although the countdown will pause at the T-4 minute mark, the team's work will not. During this 15-minute planned hold, we can expect to hear final readiness polls as NASA Launch Manager Tim Dunn and ULA Launch Conductor Scott Barney verify OSIRIS-REx, the Atlas V rocket and the Eastern Range are ready to proceed.

Weather conditions remain favorable for liftoff at 7:05 p.m. EDT. "All [launch commit criteria] are ‘go' and expected to remain ‘go' for the remainder of the countdown," Launch Weather Officer Clay Flinn told controllers.

OSIRIS-REx is headed to Bennu, a roughly spherical asteroid measuring about 1,614 feet (492 meters) in diameter. All asteroids represent remnants of the building blocks of our solar system, so why did scientists decide to send a mission to this one? Location, location, location. For a sample return mission, accessibility is key. Bennu travels in …

Overall mission management for OSIRIS-REx, including systems engineering as well as safety and mission assurance, is provided by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Dante Lauretta is the mission's principal investigator at the University of Arizona, and the spacecraft was built by Lockheed Martin Space Systems in Denver. Launch management is the responsibility …