NASA - National Aeronautics and Space Administration

Delta rockets have been carrying NASA spacecraft aloft since the 1960s, and today's Boeing Delta II has a long history of successful launches. Image at Right: Clouds of exhaust form around a Boeing Delta II launch vehicle as it blasts NASA's Swift spacecraft on its mission from Complex 17A, Cape Canaveral Air Force Station. Image credit: NASA Through the Virtual Launch Control Center, 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 II 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.

Illustration of a Delta II Rocket

Image at Left: The Delta II Launch Vehicle.
Image credit: The Boeing Company
+ View Delta II Component Definitions

T-150 minutes

Launch countdown begins Personnel not involved in the count clear the launch area; warning horn sounds

T-146 minutes

First stage helium and nitrogen pressurization begins Second stage helium tank pressurization begins

T-140 minutes

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

T-75 minutes

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)

T-20 minutes and holding Built-in 20-minute hold

Weather update Launch team polled for readiness

Image at Right: On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Delta II rocket carrying the Deep Impact spacecraft looms into the night sky. Image credit: NASA

T-20 minutes and counting

Top off liquid oxygen to 95 percent Top off helium and nitrogen pressurization system Range Safety Radio Command Carrier on

T-14 minutes

Range Safety Command Receiver checks

T-10 minutes

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 Launch enable switch to "on"

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 to internal power

T-3 minutes

Spacecraft Mission Director reports "go" for launch

Image at Left: 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 report "go" for launch

T-60 seconds

Launch enable switch "on"

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