In today's launch of the Delta IV heavy, it was stated that the starboard booster rocket would be ignited first, followed by the port and centre boosters.

I would have thought this would give some extra push which would tip the top of the rocket to port - my expectation was that they would ignite all three simultaneously.

Why do they do it this way?

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    $\begingroup$ I sort of figured they would start the center core first, not one of the side ones. The fire on launch was amazingly impressive in past launches. $\endgroup$
    – geoffc
    Aug 28, 2013 at 19:52
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    $\begingroup$ @geoffc - it was quite a good fireball today as well :-) $\endgroup$
    – Rory Alsop
    Aug 28, 2013 at 19:54
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    $\begingroup$ Nothing quite like watching a rocket launch, when the fire is higher up than the engine bells. $\endgroup$
    – geoffc
    Aug 29, 2013 at 2:09
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    $\begingroup$ All 3 boosters are held down, any tipping would be minuscule. Unlike the Shuttle, where a large torque was applied far outside the CoG and in a location that wasn't held down, yielding noticeable movement. $\endgroup$
    – Hobbes
    Sep 29, 2016 at 15:32

1 Answer 1


The starboard booster was ignited two seconds earlier as an attempt to diminish the fireball effect noticed in earlier launches.

William Graham of NASASpaceflight.com says:

The effect – caused by the rocket’s exhaust igniting hydrogen vented near the rocket – has scorched or even set fire to the first stage insulation on previous flights. While it has been observed on launches from both Vandenberg and Cape Canaveral, the effect is more severe on west-coast launches.

According to Stewart Money of Innerspace.net:

Under the new sequence, the starboard engines fires first, creating a draft which directs the gases from center and port engines down towards the launch platform.


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