Mission Information

Delta II: Countdown 101
Delta rockets have been carrying NASA spacecraft aloft since the 1960s, and today's Delta II has a long history of successful launches.

Delta II rocket launch

Image above: Clouds of exhaust form around a Delta II launch vehicle as it blasts NASA's Swift spacecraft on its mission from Launch Complex 17A at Cape Canaveral Air Force Station in Florida. Image credit: NASA

You can share in the excitement of the live countdown via NASA TV or 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 II countdown process.

T-150 minutes
  • Launch countdown begins
  • Personnel not involved in the count clear the launch area and warning horn sounds

  • T-146 minutes
  • First stage helium and nitrogen pressurization begins
  • Second stage helium tank pressurization begins
  • Turn on launch vehicle guidance system

  • T-130 minutes
  • First stage fueling begins

  • T-95 minutes
  • Weather briefing

  • T-87 minutes
  • Launch team polled for readiness to begin loading
    liquid oxygen (LOX)

  • T-80 minutes
  • Blast danger area is cleared
  • Liquid oxygen loading begins

  • T-60 minutes
  • Vehicle C-band radar transponder beacon checks begin

  • T-30 minutes
  • Perform engine gimbal steering checks (slew checks)

  • Drawing of the Delta II rocket.

    Image above: Illustration of a Delta II rocket. Depending on the payload, the size of the fairing can vary, as can the number of strap-on motors, from three, four or nine. Image credit: The Boeing Company
    › View Delta II Component Definitions

    T-15 minutes and holding
    Optional built-in hold determined by the launch window
  • Weather update
  • Launch team polled for readiness

  • T-15 minutes and counting
  • Top off liquid oxygen to 95 percent
  • Top off helium and nitrogen pressurization system
  • Range Safety radio command carrier turned on

  • T-14 minutes
  • Range Safety command receiver checks
  • Pressurize first stage fuel tank

  • T-7 minutes
  • Top off liquid oxygen to 99 percent

  • T-6 minutes
  • Verify observed weather is "go" for launch

  • T-5 minutes
  • Spacecraft to internal power (time is mission dependent)
  • Launch enable switch set to "on" position

  • T-4 minutes and holding
    Built-in 10-minute hold
  • Launch Conductor receives "go" to release from hold

  • T-4 minutes and counting
  • Arm launch vehicle and Range Safety devices
  • Launch vehicle switched to internal power

  • T-3 minutes
  • NASA launch manager reports "go" for launch

  • Liftoff of Delta II rocket.

    Image above: Emerging through the smoke and steam, the Delta II rocket carrying NASA's Deep Impact spacecraft lifts off. Image credit: NASA

    T-2 minutes
  • Raise liquid oxygen tank to flight pressure

  • T-80 seconds
  • Top off first stage liquid oxygen to 100 percent

  • T-70 seconds
  • Range reports "go" for launch

  • T-60 seconds
  • Launch enable switch set to "on" position

  • T-30 seconds
  • Liquid oxygen fill and drain valve closed

  • T-10 seconds
  • Arm launch vehicle ignition system

  • T-7 seconds
  • Go for main engine start

  • T-2.5 seconds
  • Command main engine start

  • T-0 minutes
  • Liftoff of the Delta II rocket!
    NASA's John F. Kennedy Space Center