SpaceX Falcon 9 : CRS-16 (Dragon SpX-16) : December 5, 2018 - DISCUSSION

[toruonu]

However, to your point, I'm not sure what you said really matters that much at this point, while of course there will be more robust/redundant systems, this landing attempt undeniably illustrates how much further we need things to be for propulsive landing of people (especially for the purposes of leisure travel) to become something. We can't claim BFR will be more reliable considering it hasn't even done a hop test.

Propulsive landing wasn't the issue here. Actually propulsive landing probably saved the stage and it made a soft landing. Had the stage been recovered using parachutes such spin I'd assume would tangle them and kill the chute system. So the propulsive landing IS the right choice if one were just looking at this footage Loss of a major control surface that actually worked against the system is what caused the issue here and gives though on how this will impact the BFS landings if one of the control surfaces seriously locks up.

[oldAtlas_Eguy]

There's already amateur footage of the landing attempt online.  It looks like one of the grid fins went hardover and got stuck.  Amazingly, the rocket managed to neutralize the roll and perform a soft touchdown anyway, but as it was on water it fell over and ruptured after touching down.

From the video I saw, it was still rolling during the landing / splashdown

From SpaceX the booster was still transmitting telemetry meaning it was floating and not ruptured.

[matthewkantar]

There's already amateur footage of the landing attempt online.  It looks like one of the grid fins went hardover and got stuck.  Amazingly, the rocket managed to neutralize the roll and perform a soft touchdown anyway, but as it was on water it fell over and ruptured after touching down.

From the video I saw, it was still rolling during the landing / splashdown

The last bit of video, as the legs deploy, focusing on the white spot where the leg was the rotation seemed to have stopped completely. Surprising as the roll rate was wild.

[Lars-J]

A view from the air... It landed much farther out in the ocean than it seemed from the one telephoto video:

https://twitter.com/flying_briann/status/1070392207696453632

[kevinof]

That really is damn good control - You basically had two controls working against each other all the way down and yet it did a controlled landing and no big kaboom.

Impressive stuff.

There's already amateur footage of the landing attempt online.  It looks like one of the grid fins went hardover and got stuck.  Amazingly, the rocket managed to neutralize the roll and perform a soft touchdown anyway, but as it was on water it fell over and ruptured after touching down.

From the video I saw, it was still rolling during the landing / splashdown

From SpaceX the booster was still transmitting telemetry meaning it was floating and not ruptured.

[deruch]

It was ice and it came off the booster at the lower end, not where the fins are.

No, go to the launch video and watch starting around T+5:50. The perspective is messing with you but you can clearly see that it is a small ring up close, not a bigger ring farther away from the camera. There's frames where you can see it in front of the gridfin, i.e. between the camera and the gridfin.

It may have been ice, no comment on that.  Just that it was from the area around the gridfins and actually bumped into the one on the left before it started floating up and away.

[testguy]

Still a pretty remarkable record of successful recoveries after the first landing. I suspect few in this forum would have predicted the success rate at this point. The fix to this particular problem seams pretty simple. I for one would give SpaceX an attaboy for what has been achieved to date.

[kraisee]

Watched from Cocoa Beach.   With Mk 1 eyeballs and with binoculars, it was clearly a wild ride down!

Assuming the stage landed just offshore of LZ1, ground winds are currently ~16 mph out of the NNW, so it is not going to take long before it is blown onto the beach somewhere along the peninsula.

https://www.google.com/maps/place/28%C2%B029'09.3%22N+80%C2%B032'40.1%22W/@28.4859214,-80.5795065,11129m/data=!3m1!1e3!4m6!3m5!1s0x0:0x0!7e2!8m2!3d28.4859216!4d-80.5444718

I'd imagine that a stage lying on its side with legs extended, encountering the shallow seabed, would not be good for the structure.

I hope they can get to it quickly.

Ross.

P.S. Re: The last one that landed in the ocean; we saw a squadron of 6x A-10 Warthogs arrive at Patrick AFB a day or so after the landing.   Never seen them before or since.   I believe they used that stage as live target practice because it still contained propellants and couldn't be towed safely back into Port Canaveral.   Not sure what they can do with this stage, so close to shore.

[CorvusCorax]

That really is damn good control - You basically had two controls working against each other all the way down and yet it did a controlled landing and no big kaboom.

Impressive stuff.

There's already amateur footage of the landing attempt online.  It looks like one of the grid fins went hardover and got stuck.  Amazingly, the rocket managed to neutralize the roll and perform a soft touchdown anyway, but as it was on water it fell over and ruptured after touching down.

From the video I saw, it was still rolling during the landing / splashdown

From SpaceX the booster was still transmitting telemetry meaning it was floating and not ruptured.

Yeah from the point of view of someone doing control systems, seeing this booster spin, battling aerodynamic forces and its own unresponsive actuators all the way down, and then making a recovery from such an extreme flight state and attitude and landing intact, that's like - control system porn!

I'm sure some people involved in the control system design at SpaceX will watch this over and over and over - with full telemetry visualisation. They're probably also going to show it to all new employees and interns, for years to come. This is glorious.

If they can safely recover the booster and offload the onboard data and get the hardware analyzed... thats not a failure then, its way better than a success. no success ever gives you that much awesome data to learn from! (Unless, you are doing a scientific lander mission to mars or something like that)

[oldAtlas_Eguy]

Still a pretty remarkable record of successful recoveries after the first landing. I suspect few in this forum would have predicted the success rate at this point. The fix to this particular problem seams pretty simple. I for one would give SpaceX an attaboy for what has been achieved to date.

The most important point is that they will have the actual hardware to inspect to see what failed. Whether this booster ever flies again or not is secondary.

[oiorionsbelt]

Any clues a to what boat would have been dispatched to aid the booster?

[OxCartMark]

As it slowed down, the stuck grid fins would have less authority (because there is not as much air flowing through them) and the RCS would have more authority. Makes sense that it looked more stable right as it neared a dead stop.

True that.  You could definitely see the roll rate reducing in the last 10 seconds or so.

Also, I think some of the early gyrations (as opposed to simple roll) early on could have been attributed to (once some rotation was started) the bad fin and the fins that were attempting correction rotating into and out of the airstream.  Keep in mind that at that point the stage is presented at some angle to the oncoming airstream so that the body lift can do the bulk of the horizontal movement.

Can someone in the know please comment on whether the control system and engine gimbaling would be likely to be effective at the high roll rates we saw or at the lower roll rate we saw later?  You can clearly see in the video that the engine is firing off to the side and that the direction is changing relative to the fixed ground based camera but I wonder if this was GNC and engine successfully working to do their job despite the roll or if the engine is at a fixed angle to the centerline of the stage and the redirection is only due to the roll.

[tonya]

Everyday Astronaut played a video of it a few minutes ago. Looked wild and then much calmer as landing burn started.

It looked like the leg deploy reduced the roll quite swiftly, much like an ice skater but aerodynamic drag may have slowed it more than the shifting weight.

As it slowed down, the stuck grid fins would have less authority (because there is not as much air flowing through them) and the RCS would have more authority. Makes sense that it looked more stable right as it neared a dead stop.

That makes sense, and the legs are inline with the fins. As soon as the legs start to deploy, what little airflow there is over the fins will be turbulent. I couldn't see it in the video, but likely to be RCS that killed the roll.

[mme]

A view from the air... It landed much farther out in the ocean than it seemed from the one telephoto video:

https://twitter.com/flying_briann/status/1070392207696453632

I think that this supports (admittedly as a single data point) that it probably targets the IIP offshore for a significant portion of the landing.

My biggest concern is all the concern trolly articles that will be released now. Especially for commercial crew.

[vanoord]

At what point when you don't have complete control of your rocket flying back toward land does range safety kick in? While i'm sure they are happy they got their rocket back (albeit a little wet) I expect we will need to be asking some questions about whether the automated flight termination system worked as it was designed - and if it did - who didn't trigger a manual termination and why not? Dangerous as hell.

I wonder if - as long as they've got the visual feedback in realtime - that it makes as much sense to let it drop into the ocean rather than blow it.

For a start, there's much less propellant to pollute the ocean...

[RDMM2081]

Observation: During the initial grid fin deployment, they deployed to their "flight configuration position" very slowly.  I assume this is because of the hydraulic pump issue, however the announcer clearly said something to the effect:  "The grid fins are deploying nice and slow so (some reason)".

Which is true or more likely given that we now know there was a serious issue with the grid fin hydraulic pump system?

[ugordan]

I wonder if - as long as they've got the visual feedback in realtime - that it makes as much sense to let it drop into the ocean rather than blow it.

Visual feedback has nothing to do with it any longer, F9 flies an automated flight termination system with no ground input.

[oldAtlas_Eguy]

Everyday Astronaut played a video of it a few minutes ago. Looked wild and then much calmer as landing burn started.

It looked like the leg deploy reduced the roll quite swiftly, much like an ice skater but aerodynamic drag may have slowed it more than the shifting weight.

As it slowed down, the stuck grid fins would have less authority (because there is not as much air flowing through them) and the RCS would have more authority. Makes sense that it looked more stable right as it neared a dead stop.

That makes sense, and the legs are inline with the fins. As soon as the legs start to deploy, what little airflow there is over the fins will be turbulent. I couldn't see it in the video, but likely to be RCS that killed the roll.

Transfer of momentum. When the legs deploy they transfer momentum slowing the roll. When that occurred the control system had enough authority to finish the roll dampening just before surface contact. It might have even survived a land landing.

[envy887]

Observation: During the initial grid fin deployment, they deployed to their "flight configuration position" very slowly.  I assume this is because of the hydraulic pump issue, however the announcer clearly said something to the effect:  "The grid fins are deploying nice and slow so (some reason)".

Which is true or more likely given that we now know there was a serious issue with the grid fin hydraulic pump system?

The TI fins have always deployed much more slowly than the aluminum ones. That didn't look unusual to me.

[Scylla]

Observation: During the initial grid fin deployment, they deployed to their "flight configuration position" very slowly.  I assume this is because of the hydraulic pump issue, however the announcer clearly said something to the effect:  "The grid fins are deploying nice and slow so (some reason)".

Which is true or more likely given that we now know there was a serious issue with the grid fin hydraulic pump system?

Titanium fins have always deployed much slower than aluminum fins.

Argg....Ninjad...