SpaceX F9 - CRS-16 - SLC-40

[mongo]

Could still see land 20 seconds before touchdown on the booster cam. (nauseating)

 

[HVM]

They need bigger cup of rice that with the fairing...

 

[mongo]

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.

If the center engine is on the center line, I'm not sure how it had any spin authority since there would be no lever arm to work against. Could the fuel itself be the stabilizing factor, both in terms of slosh friction and offsetting the CG to allow the center engine some moment arm?

 

[nwdiver]

Let's call it a successful failure.

Good news is that future boosters will have better hydraulic pumps.

I think that what was really impressive is that the F9 was largely able to compensate for the failed hydraulic pump. It sure looked like it COULD have landed but they sent it out over water as a safely measure.

 

[SMAlset]

Couldn't be around to see this launch and will rewatch later. Did watch the video someone posted a few posts back however. Our news just mentioned the launch and that worms were going to the station but no mention of Stage 1. What caused the spin? uneven firing of the landing boosters? Would have been amazing if it didn't tip over given it was still spinning close to land.

 

[Mike1080i]

If the center engine is on the center line, I'm not sure how it had any spin authority since there would be no lever arm to work against. Could the fuel itself be the stabilizing factor, both in terms of slosh friction and offsetting the CG to allow the center engine some moment arm?

I agree, it seems unlikely a center engine only landing burn could stop the roll. However, it would be decelerating the stage and that would mean less and less force acting on a stuck grid fin. I'm a little surprised the roll didn't push propellant away from the inlets so the engine could ignite and continue to burn.

 

[mongo]

I agree, it seems unlikely a center engine only landing burn could stop the roll. However, it would be decelerating the stage and that would mean less and less force acting on a stuck grid fin. I'm a little surprised the roll didn't push the propellant away from the inlet so the engine could ignite and continue to burn.

Upon further thought (and an apple), if the stage is tumbling (or whatever you call a tilted spin), then the center engine is offset from the CG/ axis of rotation and can provide spin stabilization. As long as it cancels the spin before canceling the tilt.

Good point on starvation, the deceleration forces and tank level must have been sufficient to keep the intake filled.

 

[Mike1080i]

I think that what was really impressive is that the F9 was largely able to compensate for the failed hydraulic pump. It sure looked like it COULD have landed but they sent it out over water as a safely measure.

It was impressive that the stage handled the issue as well as it did. As I understand it, the stage is targeting a point just off shore just in case of a failure. It only diverts from that point to the landing pad after the landing burn has started. If so, it seems to have performed as intended.

 

[SMAlset]

Always interesting to watch nonetheless!

 

[nwdiver]

It was impressive that the stage handled the issue as well as it did. As I understand it, the stage is targeting a point just off shore just in case of a failure. It only diverts from that point to the landing pad after the landing burn has started. If so, it seems to have performed as intended.

Makes sense. I wonder if it would be worth having a barge anchored offshore in the future just in case. I'm sure that booster costs >$10M... seems like it might be worth it... Not a drone ship, just a barge as a backup landing site.

 

[bxr140]

Some pretty hard engine gimbaling in the DIY video too...

 

[Mike1080i]

Upon further thought (and an apple), if the stage is tumbling (or whatever you call a tilted spin), then the center engine is offset from the CG/ axis of rotation and can provide spin stabilization. As long as it cancels the spin before canceling the tilt.

Good point, that could be a possibility.

 

[Mike1080i]

Makes sense. I wonder if it would be worth having a barge anchored offshore in the future just in case. I'm sure that booster costs >$10M... seems like it might be worth it... Not a drone ship, just a barge as a backup landing site.

I doubt a barge landing would have been successful anyway as it appears to have been in a slow roll all the way to the surface. Probably better to solve the issue so it doesn't happen again.

 

[ecarfan]

if the stage is tumbling (or whatever you call a tilted spin), then the center engine is offset from the CG/ axis of rotation and can provide spin stabilization. As long as it cancels the spin before canceling the tilt.

I don’t know if the center engine gimbal can react quickly enough and can move through a sufficiently large arc to stabilize a spin of that magnitude.

 

[e-FTW]

Spins are bad: Goose would still be with us if it weren't for one of those. ;-)

 

[e-FTW]

Elon's tweet shows the rest of the landing:
Elon Musk on Twitter

This video shows one of the most amazing things I've seen SpaceX pull off.

 

[MacGreiner]

Spins are bad: Goose would still be with us if it weren't for one of those. ;-)

Flat spin.

 

[MacGreiner]

Looked to me like it was the landing leg deployment that actually arrested the spin.

 

[HVM]

D. Stamos/Helodriver (@SpacecoastPix) | Twitter

 

[ecarfan]

I realize this probably had nothing to do with the grid fin issue, but it was odd looking Luka Bakhsoliani on Twitter