CRS 16 Booster Question

[scaesare]

So in thinking about the aborted booster landing from CRS 16 a while back (the one with the locked grid fin that went in the spin), I have a question as to how it was corrected.

From Elon's comments, he said the engine worked to overcome the rotation of the booster. The captured video does indeed show the engine gimbaling madly and the booster does slow or even stop rotation just prior to the water touchdown.

My question is how? With a single center mounted engine that can gimbal, how was it able to correct for rotational momentum? It would seem that would require something offset form center, otherwise you'd only be able to correct for yaw or pitch.

If this has already been covered, my apologies... any pointers appreciated.

Thanks.

 

[Grendal]

So in thinking about the aborted booster landing from CRS 16 a while back (the one with the locked grid fin that went in the spin), I have a question as to how it was corrected.

From Elon's comments, he said the engine worked to overcome the rotation of the booster. The captured video does indeed show the engine gimbaling madly and the booster does slow or even stop rotation just prior to the water touchdown.

My question is how? With a single center mounted engine that can gimbal, how was it able to correct for rotational momentum? It would seem that would require something offset form center, otherwise you'd only be able to correct for yaw or pitch.

If this has already been covered, my apologies... any pointers appreciated.

Thanks.

It was discussed before but such questions are enlightening for those that aren't following the details day to day. Scott Manley lays it out pretty well.

 

[scaesare]

Ahh you know what, I looked at his vids to see if he addressed it and missed it... thanks @Grendal !

 

[scaesare]

So I just watched this and it's interesting, but:

1) Primarily addresses the angular momentum of the leg deployment, which wasn't my question

2) Claims it was the RCS thrusters that stopped the rotation.


I'm pretty sure in the post-launch interview Elon said it was the engines gimballing that counteracted the rotation. This tweet seems to confirm:

Was he just incorrect here?

 

[Yggdrasill]

I think the rocket gimbaling can in fact slow down the rotation, as the rocket is not rotating entirely vertically.

As long as the axis of rotation is perfectly though the center of the booster, the gimbaling can't do anything, but if you suppose the axis of rotation had been shifted 90 degrees (so it would rotate like if you spin a pencil on a flat surface), and the engine could gimbal 90 degrees, it could easily stop the rotation.

Now the rotation isn't nearly that far off center, and the engine doesn't gimbal nearly that much, but it will be able to slow down the rotation, over time.

 

[scaesare]

I think the rocket gimbaling can in fact slow down the rotation, as the rocket is not rotating entirely vertically.

As long as the axis of rotation is perfectly though the center of the booster, the gimbaling can't do anything, but if you suppose the axis of rotation had been shifted 90 degrees (so it would rotate like if you spin a pencil on a flat surface), and the engine could gimbal 90 degrees, it could easily stop the rotation.

Now the rotation isn't nearly that far off center, and the engine doesn't gimbal nearly that much, but it will be able to slow down the rotation, over time.

Hmmm...

I can see your point about correcting the off-center pitch/yaw (and there was indeed some of that in the video), but would that affect angular momentum (I.e. body spin) ant all?

 

[Grendal]

I think the rocket gimbaling can in fact slow down the rotation, as the rocket is not rotating entirely vertically.

As long as the axis of rotation is perfectly though the center of the booster, the gimbaling can't do anything, but if you suppose the axis of rotation had been shifted 90 degrees (so it would rotate like if you spin a pencil on a flat surface), and the engine could gimbal 90 degrees, it could easily stop the rotation.

Now the rotation isn't nearly that far off center, and the engine doesn't gimbal nearly that much, but it will be able to slow down the rotation, over time.

If so, then I'd say that it was a combination of RCS thrusters and gimbaling to slow rotation. I think this video gives a better view of what was happening with the engine gimbaling. The amount of control still being exhibited is impressive.

 

[e-FTW]

All of this confirms that SpaceX has superhero engineers.