OSIRIS-REX (Origins, Spectral Interpretation, Resource Identification, and Security - Regolith Explorer)

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 …