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Countdown 101: Delta IV

A Delta IV rocket lifts off from the pad. 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

  • A Delta IV heavy rocket rests on its launch pad. 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

  • A Delta IV rocket sits enclosed within its service structure. 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




  • Find this article at:
    http://www.nasa.gov/mission_pages/launch/delta_IV_count_101.html