Author Topic: SpaceX Falcon 9 : CRS-16 (Dragon SpX-16) : December 5, 2018 - DISCUSSION  (Read 255699 times)

Online catdlr

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Here's my question...If the stage knows it's aborting a pad landing to land on the ocean, why then lower the legs at all?  Would it then make lifting onto a barge eaiser with the legs connected to the stage?
It might allow the legs to take some of the impact instead of the engines taking it all.

Great answers:  Thanks CorvusCorax and Nomadd.
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Offline Lars-J

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Its always possible I'm simply overrating my interpretation of the Mark 1 eyeball, so you could be right. It could also be that the vehicle's quick rotation is obliterating the visibility of the cold gas plumes, but it certainly doesn't look very much like previous large "firings" of their nitrogen RCS thrusters.



Yes, I think you are overrating your mark 1 eyeball. The light conditions are different - and the background. In the video there, note how much lighter the RCS plume looks against the ocean background... Almost like the sky color would be? And then look again at the tracking footage that Elon tweeted. Against a sky background.

Another point which may explain the RCS plume being less visible at touchdown might be that it actually ran out... or almost did. I bet this landing used up more then the average nitrogen gas.
« Last Edit: 12/06/2018 06:30 am by Lars-J »

Offline woods170

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Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins. AFTS is for ascent only. Why do you think the initial aiming point for landing is out to sea?
Exactly because AFTS is not active during entry and landing.

Offline niwax

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Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins. AFTS is for ascent only. Why do you think the initial aiming point for landing is out to sea?
Exactly because AFTS is not active during entry and landing.

AFTS is also pointless on landing, it just makes sure you scatter debris over the entire launch site. It works when your velocity vector is pointing away from the launchpad.
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Offline kevinof

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I also think the optics of even a controlled termination is far worse than an intact stage gently landing on the water intact.

If you're going to have a failure, make it a good one.

Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins. AFTS is for ascent only. Why do you think the initial aiming point for landing is out to sea?
Exactly because AFTS is not active during entry and landing.

AFTS is also pointless on landing, it just makes sure you scatter debris over the entire launch site. It works when your velocity vector is pointing away from the launchpad.

Offline ugordan

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Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins.

It is safed *after* the entry burn.

Offline MaxTeranous

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Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins.

It is safed *after* the entry burn.

If the entry burn fails, the stage breaks apart anyway doesn't it ?

Offline CraigLieb

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If this were the 1950-60s, we'd be talking about the unbelievable skills of the pilot who wrestled the craft all the way to the ground and regained control at literally the last moment to soft land his aircraft intact....

Good job Major Tom!

Dare I say, the avionics aboard B1050.1 has "The Right Stuff"?!

Maybe this "black box" could be Time magazine's Computer of the Year?  (Is Time still relevant?)
It’s the people that designed and implemented the control strategy you can recognize. Three cheers for the dedicated team of software and hardware designers that created this amazing vehicle and system.
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Offline Step55

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From "the camera that shall not be named", looks like they are loading some equipment onto OCISLY. Just saw them load to pallet sized objects onto the deck with the small crane.

Offline jpo234

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If this were the 1950-60s, we'd be talking about the unbelievable skills of the pilot who wrestled the craft all the way to the ground and regained control at literally the last moment to soft land his aircraft intact....

Good job Major Tom!

Dare I say, the avionics aboard B1050.1 has "The Right Stuff"?!

Maybe this "black box" could be Time magazine's Computer of the Year?  (Is Time still relevant?)
It’s the people that designed and implemented the control strategy you can recognize. Three cheers for the dedicated team of software and hardware designers that created this amazing vehicle and system.

That would be Lars Blackmore's team.

https://twitter.com/larsblackmore/status/1070459490867142656

« Last Edit: 12/06/2018 11:57 am by jpo234 »
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Offline quagmire

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I am surprised there wasn't a plan in place to recover a booster after a water landing. Especially after the 1st stage that survived its intentional water landing, but had to be destroyed. One would think a plan would have been made on how to recover a booster bobbing in the water after they had to destroy that one.
« Last Edit: 12/06/2018 12:23 pm by quagmire »

Offline edzieba

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After the previous 'water landing' (B1032) that was successful but could not be recovered due to booster safety, I wonder if some splashdown-specific code was added (or even some minor hardware mods) to allow for the booster to reliably safe itself in the event of a splashdown. Approach to the booster seems to have been more blase than B1032, though it could just be that its presence near a major port and waterway (and proximity to land, and floating along the cost uncontrolled) was deemed as more of a hazard than approaching it with manned craft.
Dare I say, the avionics aboard B1050.1 has "The Right Stuff"?!

Maybe this "black box" could be Time magazine's Computer of the Year?  (Is Time still relevant?)
With the spin arrested by the leg deployment, and the leg pneumatic cylinders (and legs themselves) being made of CF, "Inanimate Carbon Rod" is still in the running!

Offline woods170

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Frankly, I'm surprised the AFTS didn't terminate and it still executed a soft landing off shore.

AFTS is saved before the entry burn begins.

It is safed *after* the entry burn.

I looked it up and you are correct. But, that still leaves the stage without AFTS after the initial aiming point has been established (via the entry burn and assumed ballistic entry from that point forward).

In short: by the time the the flight computer senses that the grid fins are not responding there is no active AFTS present to trigger a self-destruct.

Offline SciNews

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Hans Koenigsmann, SpaceX Vice President of Mission Assurance, about the anomaly

Offline RoboGoofers

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I think the anti slosh baffles had a lot to do with stopping the spin.

Online LouScheffer

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It was the leg deployment that did most of the work.  And the same change in rotational inertial would have made it harder for the control system.
This assertion is contradicted by the onboard footage. The roll is mostly nulled by the time the legs begin to deploy.
I don't really agree with that, the instant the legs pop out the roll basically stops.
Both assertions are true.  Using, we can use the time the shadow passes the tip of the left fin to measure the rotation rate.  Times are measured as youtube time + frames.
1:47 + 15/30
1:49 + 14/30
1:51 + 13/30
1:53 + 17/30
1:55 + 24/30
1:58 + 3/30
2:00 + 19/30
2:03 + 13/30
2:06 + 25/30
----- Legs come out
then about 1/4 more turn in 4 seconds.

So the roll rate was dropped from 1+29/30 (1.966) seconds per turn to 3+12/30 (3.40) seconds per turn before the legs came out, and was decreasing quite quickly. (By extrapolation, the next turn would have taken about 4 seconds.) But the legs also had a big effect, reducing the remaining roll rate by a factor 2-4.

EDIT: fix typo in last time.
« Last Edit: 12/06/2018 01:55 pm by LouScheffer »

Offline OxCartMark

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There's a lot of marine radio traffic involving our ships but I don't have time to listen and transcribe as I did last night.  Anyone?

https://www.broadcastify.com/listen/feed/21054/web
Actulus Ferociter!

Offline envy887

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Latest Elon tweet update-

"Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines."

Block 5.1

They have already made other changes to Block 5, like the new COPVs. Don't expect a new block yet.

Offline rsdavis9

Is the grid fin hydraulic motor powered by an electric motor?
I thought at first they used a hydraulic reservoir with gas pressure.
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Offline OxCartMark

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I don't know whether the power source is electric or something else but I know that its no longer operated by a pressurized reservoir and the fluid disposed of overboard.  They're using a closed loop system with a pump now and have been for a long time, likely soon after they ran out of fluid on one of the early landings which was about the time that it became apparent that grid fins were getting the job done and it was worth investing more in them.
Actulus Ferociter!

Tags: CRS-16 
 

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