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Launch Timeline
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Delta II Rocket Countdown
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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
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| 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
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| T-130 minutes |
- First stage fueling begins
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| T-95 minutes |
|
| T-87 minutes |
- Launch team polled for readiness to begin loading
liquid oxygen (LOX)
|
| T-80 minutes |
- Blast danger area is cleared
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| T-75 minutes |
- Liquid oxygen loading begins
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| T-60 minutes |
- Vehicle C-Band radar transponder beacon checks
begin
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| T-30 minutes |
- Perform engine gimbal steering checks (slew
checks)
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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
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| T-14 minutes |
- Range Safety Command Receiver checks
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| T-10 minutes |
- Pressurize first stage fuel tank
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| T-7 minutes |
- Top off liquid oxygen to 99 percent
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| T-6 minutes |
- Verify observed weather is "go" for launch
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| T-5 minutes |
- Spacecraft to internal power
- Launch enable switch to "on"
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T-4 minutes and
holding
Built-in 10-minute hold |
- Launch Conductor receives "go" to release from
hold
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| T-4 minutes and counting |
- Arm launch vehicle and Range Safety devices
- Launch vehicle to internal power
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| 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
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| T-80 seconds |
- Top off first stage liquid oxygen to 100 percent
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| T-70 seconds |
- Range report "go" for launch
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| T-60 seconds |
- Launch enable switch "on"
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| T-30 seconds |
- Liquid oxygen fill and drain valve closed
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| T-10 seconds |
- Arm launch vehicle ignition system
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| T-7 seconds |
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| T-2.5 seconds |
- Command main engine start
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| T-0 minutes |
- Liftoff of the Delta II rocket!
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NASA's John F. Kennedy Space
Center
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