2)If that failed engine is not the central one but one of eight peripheral engines, the total thrust vector will not pass through the center of mass, that will cause rotation round center of mass. I think engines need use "Gimbal Capability" to counteract that rotation.Is it possible to shut down another engine that locate at symmetrical position?
IIUC, right now the Merlins only have a single throttle point. So no throttle-up would be available to compensate, nor throttle-down to g-limit. Engines would have to shut off to g-limit.
the root cause of the F1.2 failure was not slosh or the first stage hitting the second. It was whatever caused the first stage to rotate.
This rotation was caused partly by the Merlin engine pointing slightly off center-of-mass at shutdown. However, analysis now indicates that a majority of the rotation was caused by increased aerodynamic forces acting on the 2nd stage and fairing, due to the vehicle being lower than expected during stage separation and at a high angle of attack.With corrections to the mixture ratio and helium pressurant margins, as well as improved thrust and Isp from the Merlin 1C engine that will be used in all future flights, the separation altitude will be considerably higher and aerodynamic forces will not be a factor. Merlin shutdown will also be initiated at a lower acceleration.
There is high confidence that LOX slosh was the primary contributor to this instability...Falcon 1 did not use slosh baffles in the second stage tanks, as simulations done prior to flight indicated the slosh instability was a low risk. Given that in space there are no gust or buffet effects, the simulations did not take into account a perturbation, as occurred due to the hard slew maneuver after stage separation. Extensive 2nd stage slosh baffles will be included in all future flights, as is currently the case with the 1st stage.
