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
Launch Countdown Begins
T-290 minutes
Begin cryogenic propellants loading
Begin Common Booster Core liquid oxygen (LOX) tank loading
T-220 minutes
Begin Common Booster Core liquid hydrogen (LH2) tank loading
T-180 minutes
Weather briefing
T-175 minutes
Begin second stage LOX tank loading
T-160 minutes
Begin second stage LH2 tank loading
T-85 minutes
Perform telemetry RF link checks
T-70 minutes
Perform Command Receiver Decoder testing
Image to right: The mammoth Delta IV Heavy awaits launch from its launch pad. Credit: Boeing
T-50 minutes
Begin RS-68 engine spin start pressurization
Perform launch pad gantry swing arm functional test
Perform RS-68 engine gimbal steering "slew" check
T-25 minutes
Weather briefing
T-8 minutes
Arm launch pad ordnance
Image to right: The mammoth Delta IV Heavy awaits launch from its launch pad. Credit: Boeing
T-5 minutes and holding
Enter 15-minute planned hold
Weather update
Transfer spacecraft to internal power
Launch Conductor Readiness Poll
Mission Director Readiness Poll
T-5 minutes
Transfer launch vehicle to internal power
T-4 minutes
Arm safe and armed switches
T-3 minutes
Common Booster Core LOX secure at flight pressure and flight level
Common Booster Core LH2 secure at flight pressure and flight level
T-2 minutes
Second stage LOX securing started
Vehicle hydraulic pressure verified at 4000 psi
T-90 seconds
Second stage LOX secure at flight pressure and flight level
LOX ground support equipment secure
T-80 seconds
Second stage LH2 securing started
Range reports go for launch
T-50 seconds
Second stage LH2 secure at flight pressure and flight level
Image to right: A Boeing Delta IV Medium-plus rocket stands inside its mobile service tower. Credit: NASA/George Shelton
T-45 seconds
Launch enabled "on"
Main power turned "off"
T-25 seconds
Solid Rocket Motor Thrust Vector Control System Blowdown
T-15 seconds
Launch vehicle igniters armed
Radially Outward Firing Initiators ignition
T-4.5 Seconds
RS-68 main engine ignition
T-0
Liftoff of the Delta IV rocket