The Delta IV is a new model of rocket from Boeing. The vehicle is capable of carrying single or
multiple payloads weighing between 9,480 to 28,620 pounds. Once in space, the Delta IV can place spacecraft in polar, sun-synchronous, geosynchronous, geosynchronous transfer and low-Earth orbits..

Image to right: A Boeing Delta IV Medium-plus rocket lifts off from its launch pad. Credit: Boeing/Carleton Bailie

At the heart of the Delta IV is the first stage Common Booster Core, which features a liquid oxygen- and hydrogen-powered RS-68 engine. The second stage engine is a Pratt & Whitney RL10B-2, also fired with the same propellant combination.

The Detla IV can be outfitted in various configurations to lift medium, medium-plus, and heavy satellites and spacecraft:

Delta IV Medium: One Common Booster Core first stage topped with a second stage engine.

Delta IV Medium-plus: One Common Booster Core with two or four strap-on solid rocket motors and topped with a second stage engine.

Delta IV Heavy: Three Common Booster Cores joined together and topped with a second stage engine.

Follow the Countdown Live on the Internet
Through the Launch Blog, you can share in the excitement of each new launch with live coverage directly to your computer via the Web. Coverage usually begins two hours prior to liftoff, and you can use the countdown events below to track the prelaunch milestones and learn about the Delta IV countdown process.

Live launch commentary is also provided on NASA TV.

Here are some countdown milestones and key events that take place after the countdown begins. Keep in mind that event times and lengths are approximate and subject to change.

T-315 minutes