SpaceX Falcon 9 v1.1 - Jason 3 - SLC-4E Vandenberg - Jan 17, 2016 - DISCUSSION

[leetdan]

Considering top vs. bottom view, how much is generally known about the inner plumbing and structure?  Is there anything trade secret or ITARS related that would prevent them from releasing an image from that angle?

Compare to engine bell pictures of which there are many in the public domain.

[Johnnyhinbos]

If only there was some device that could accurately measure the height of the ocean at a given point. Oh, wait...

[DecoLV]

Since everyone else if offering their armchair engineering today, I'll offer mine: A $2.00 kickstand that flips out from the side of the rocket body when a bubble level switch + logic tells it the landed stage is tipping over. No more boom, stage saved. Done.

[CameronD]

I'm wondering if one of you talented people could estimate the up and down movement of the ASDS from the video prior to the freeze. There is a section on the video feed of the launch that shows the horizon relative to the deck throughout a couple of peaks and valleys. It would be interesting to know the exact wave heights and deck movement for future ASDS landing attempts.

From what I read of it, wind seems light (under 10kts at a guess) but there's a big swell running. ..definitely time to dole out the sea-sickness tablets.

 

[edkyle99]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

[meekGee]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

I'm nursing the theory that the sea state or wind state mess with the landing timing, and one of the legs touched down before locking.

[Lars-J]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

It might have contributed. But then again the sea state might have toppled it over even if it landed correctly.

[Jim_LAX]

Maybe the landing software needs to be made "wave smart" during the last few seconds before touch down.  Just my thoughts.

[Herb Schaltegger]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

It might have contributed. But then again the sea state might have toppled it over even if it landed correctly.

Apparently someone in the morass of hellish UI and rotten humanity that is Reddit did an analysis with a not-obviously-wrong numbers for stage, octoweb and engine mass, and determined that the the roll or pitch angle would have to exceed 23º or so for the stage to be at risk of tipping. I saw nothing remotely close to that in the pre-landing views of JRtI.

[Lars-J]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

It might have contributed. But then again the sea state might have toppled it over even if it landed correctly.

Apparently someone in the morass of hellish UI and rotten humanity that is Reddit did an analysis with a not-obviously-wrong numbers for stage, octoweb and engine mass, and determined that the the roll or pitch angle would have to exceed 23º or so for the stage to be at risk of tipping. I saw nothing remotely close to that in the pre-landing views of JRtI.

Oh cool, I stand corrected. Now that I think about it, the stage is bottom heavier than it looks. Hopefully the leg pads has a lot of friction so it wouldn't slide around. 

[mfck]

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

It might have contributed. But then again the sea state might have toppled it over even if it landed correctly.

The stage has probably more than half of it's weight in the lower third of it's height and with its aspect ratio being about 1:3 base to height, you'd need the surface to pitch or roll about 30° to topple it. I don't think the swell was that bad in the video. IMBW.

Edit. Ninja'ed...

[Robotbeat]

It's an empty pop can with a steel weight in the bottom.

[NovaSilisko]

I'd worry about it sliding before I'd worry about it tipping.

[CameronD]

You'd hope SpaceX have thought of that already.

Subsequent news that the leg did not lock.  Does this mean that the sea-state did not in the end play a decisive role in the landing result?

 - Ed Kyle

It might have contributed. But then again the sea state might have toppled it over even if it landed correctly.

Apparently someone in the morass of hellish UI and rotten humanity that is Reddit did an analysis with a not-obviously-wrong numbers for stage, octoweb and engine mass, and determined that the the roll or pitch angle would have to exceed 23º or so for the stage to be at risk of tipping. I saw nothing remotely close to that in the pre-landing views of JRtI.

Statically or dynamically??  My calculations around rolling and pitching of the ASDS as shown in the webcast would have the stage going overboard a long way before 23º..  Imagine one leg being "punched upward" as it hit the deck whilst the corresponding side drops away slightly.

Of course the N2 thrusters would be going full-tilt at that point, so it's more of a "what if they failed" scenario and hopefully not all that likely in actual practice.
 

[Rocket Science]

I'd worry about it sliding before I'd worry about it tipping.

Need to string some arrestor cables across the deck...

[AJA]

They've got a picture right before landing!
https://twitter.com/SpaceX/status/688905957422706688

I can't for the life of me model anything on short notice, but here's an exceedingly quick representation of what it looks like we're seeing, first in a perspective similar to the camera, then in an imaginary view from a bird's eye perspective. The piles of scorched crap visible in the foreground of the photography are what's left of the tankage.

That's a compelling interpretation to be sure, but then the bit of the leg that's visible seems discoloured. So I'm leaning toward thinking that it's the outside - i.e. away from stage body - surface of the leg (which becomes the inside when in landing configuration, since the legs flip over).

Are the water cannons spraying salt or fresh water? If fresh, it seemed like they had them started up fairly early (though maybe they just have huge tanks and don't care). If salt, were they supposed to track the stage as it came in? Seems like maybe not the best idea to spray salt water at things. Or maybe they were spraying water on something else entirely...?

Seems like they would need a boatload (literally) of fresh water to maintain it that long.

I too, would like to know of the answer to this...

Radar altimeters are small and cheap, you can have one in each leg.


However, I think you want to know the state of the barge from further away, so the correction is 50 seconds aways, not 5...

Doesn't the stage already have one? Instead of having individual ones on each leg, which would add to radio-noise, and interference with one-another; would you rather have a positional (perhaps angular) indicator, and maybe even some strain gauges (to account for bending) along the legs... to know of their positions relative to the stage?

[Tuts36]

They've got a picture right before landing!
https://twitter.com/SpaceX/status/688905957422706688

Damn.  That looks like a 4 point, straight up landing, at least from this angle.

[Rocket Science]

X marks the spot!!

[Mongo62]

Damn.  That looks like a 4 point, straight up landing, at least from this angle.

Which matches what was tweeted, that it made a good landing only 1.3m from the center of the bullseye, but one of the legs was not latched and it fell over after landing.

[punder]

Beautiful (and poignant) photo, thanks AJA.

The explosion would originate in the compromised fuel tank, adjacent to the open "inside" surface of the leg. So I still think it's the top of the octaweb that is visible, not the bottom. But in any case, the whole thing would be enveloped momentarily in a cloud of burning kerosene... So discoloration would be everywhere.