I don’t know yet if the loss off control was due to a malfunctioning grid fin, or cold gas thruster, or an internal guidance system, or something else.
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SpaceX F9 - CRS-16 - SLC-40
- Thread starter MacGreiner
- Start date
I'd say the control system did compensate amazingly, as seen by attitude control and minimal yaw rate. It just wasn't able to overcome the lack of grid fin induce side slip/ tilt. Not sure anything could have without extra engine burns.
Thanks, so glad to hear that the cause is already known. While I was composing my lengthy post with screen caps, of course multiple posts came in and I did not scroll back far enough to see the one showing Elon’s tweet.
Let's call it a successful failure.
Good news is that future boosters will have better hydraulic pumps.
More tweets from Elon on the grid fin failure.
e-FTW
New electron smell
I think we have video here: SpaceX CRS-16 Launch LIVE - IRL from KSC - Twitch
(Scroll to one hour in, am on my phone here)
The spin seems to stop right before “landing”. Just nuts!
(Scroll to one hour in, am on my phone here)
The spin seems to stop right before “landing”. Just nuts!
Overall, this was incredibly impressive. There was a failure causing the booster to lose significant control. Everyday Astronaut video has some footage and you can see the booster was spinning and, not quite, tumbling. The landing burn began and almost completely righted the booster and allowed a soft water landing. It's hard to say whether it would stayed up if it tried the landing on the pad. It would have probably made it from the looks of that last moment of the landing. SpaceX is incredible.
If only NASA had agreed to use a “flight proven” booster perhaps this would not have happened. 
Better and direct link here:
Twitch
It touched down very softly before falling over due to landing on water despite spinning quite a bit.
Thanks for that link. Wow. It didn’t look as severely out of control from that point of view as it did from the camera on the stage. Very close to landing upright, but since it was in the water it of course could not stay upright. The person shooting that video could not see that the stage was not touching down on land, I assume.
Elon's tweet shows the rest of the landing:
Elon Musk on Twitter
Here's the bystander's (Das Valdez) video:
Elon Musk on Twitter
Here's the bystander's (Das Valdez) video:
I think that's a valid case.
Near as I can tell from the landing clip, the 'opposite' grid fin actually retracted a bit. It makes sense that such a loss of control would induce a difficult-to-recover roll. I think the control algorithm did a pretty solid job; I think the biggest roadblock to success was time--it took too much time to stabilize, which didn't leave enough time to target.
Edit: Elon's tweet poo-poos that a little, maybe a bit of retraction but not much.
Where we were at the LC-39 gantry position it looked like it landed successfully so it must only touched down only just out from LZ1.
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Thinking about it, it makes sense that the much more powerful gimbled rocket motor was able to wrest control away from the grid fins and reverse a pretty severe spin. I wouldn't be surprised if SpaceX learned from this and have the rocket turn on early to combat grid fin failures if this happens again (assuming there is enough propellant for that). Pretty impressive nonetheless.
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