All the engines of the Delta IV are not ignited at the same time: One of the lateral engine is started few seconds before the other. I imagine there is a good reason for not starting all engines at once (this feature is also observed on other launchers such as the Saturn V)

Given one booster starts earlier and its engine burns several hundred kg of propellant per second (172500 kg of LOX + 29500kg of LH in 245s), it may provoke an unbalance in launcher mass repartitions. How is that handled?


1 Answer 1


The engines on the Delta IV Heavy, like most large liquid-fueled engines, can gimbal, vectoring up to 6º in any direction, so any mass imbalance can be corrected for almost instantly.

That said, it would also be possible to just start with a couple hundred kg of propellant more in the tanks on the booster that lights first; propellant tanks are generally not loaded 100% full.


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