Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 3  (Read 484821 times)

Online Lar

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More grid fin stuff is off topic. Take it to the thread pointed out a few posts back. Or else your posts walk the plank. Savvy?
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline starhawk92

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Where would the repairs to the ASDS happen?  Can they fix it where it berths, or does it go to another port with the proper equipment and materials?  I lived in Kansas for a long time, so I know nothing about the sea/am the ultimate landlubber.

Thanks!

Offline Kabloona

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Where would the repairs to the ASDS happen?  Can they fix it where it berths, or does it go to another port with the proper equipment and materials?  I lived in Kansas for a long time, so I know nothing about the sea/am the ultimate landlubber.

Thanks!

The barge owner, McDonough Marine, is based on the Louisiana Gulf Coast, and that's where the barges have had their wings installed.

But hopefully this damage is minor enough that it can be done at Port Canaveral.  Welding equipment and steel plate are portable, as are experienced welders, and welding can be done even underwater if necessary (I just learned this by watching "Deadliest Job Interviews."  ;))

Offline cscott

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And JRtI had its wings installed in port, not at the Louisiana shipbuilder.
« Last Edit: 03/10/2016 02:37 PM by cscott »

Offline Kabloona

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And JRtI had its wings installed in port, not at the Louisiana shipbuilder.

Yes, good point. I forgot that minor operation.  ;)

Offline Kabloona

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FCC permit for CRS-8 transmitters:

https://apps.fcc.gov/oetcf/els/reports/STA_Print.cfm?mode=current&application_seq=69496&RequestTimeout=1000

ASDS location is given as 30.5 degrees N, 78.5 degrees W.

Permit does not guarantee an ASDS landing attempt on CRS-8, but it is apparently an option if they can get the repairs done fast enough.

Here are some more photos of the ASDS I took today. Drone, Panorama, and some shots from the Exploration Tower.

Full Album:

(Also caught a delta stage rolling up to the base)

http://imgur.com/a/SHt5g

Online gadgetmind

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So does it have a big hole dead centre or not? Most pictures say not, the first aerial view suggests it does, but maybe a bit of photoshop?

Offline OxCartMark

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I was the one that speculated that there may have been a hit dead center.  Shadows from scrap that was nearby was the other possibility.  This and other pictures prove that there never was a hard hit there.

But on the other side, the newly exposed bottom side, there appear to be more barnacles than I've ever seen in one place, about 2/3 of an acre of them.

edited, meant to say "never was" not "never wasn't".
« Last Edit: 03/11/2016 02:44 AM by OxCartMark »

Offline OnWithTheShow

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I was the one that speculated that there may have been a hit dead center.  Shadows from scrap that was nearby was the other possibility.  This and other pictures prove that there never wasn't a hard hit there.

Do you mean "never was"?

Offline Okie_Steve

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Anyone know enough about metallurgy to estimate the minimum force required to puncture the steel plating?
That and dry mass would give a lower bound on the velocity at contact.

Offline Kabloona

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Anyone know enough about metallurgy to estimate the minimum force required to puncture the steel plating?
That and dry mass would give a lower bound on the velocity at contact.

I think we have a reasonable idea of deck plate thickness, well enough to make a meaningful guesstimate, but the result will be strongly influenced by the assumed contact area, which in turn depends on angle of impact, how the aft end of the stage deforms on impact, etc, etc.

OxCartMark did a detailed calculation a while back assuming all the steel plate in the barge was of equal thickness, and he got a result of 1" thick all around, so I'd trust that number as being in the right ballpark.

http://forum.nasaspaceflight.com/index.php?topic=36326.msg1341509#msg1341509
« Last Edit: 03/10/2016 10:34 PM by Kabloona »

Offline mme

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Here are some more photos of the ASDS I took today. Drone, Panorama, and some shots from the Exploration Tower.

Full Album:

(Also caught a delta stage rolling up to the base)

http://imgur.com/a/SHt5g
Thanks!  Is that a person I see inside?
« Last Edit: 03/10/2016 10:35 PM by mme »
Space is not Highlander.  There can, and will, be more than one.

Online AncientU

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Anyone know enough about metallurgy to estimate the minimum force required to puncture the steel plating?
That and dry mass would give a lower bound on the velocity at contact.

I think we have a reasonable idea of deck plate thickness, well enough to make a meaningful guesstimate, but the result will be strongly influenced by the assumed contact area, which in turn depends on angle of impact, how the aft end of the stage deforms on impact, etc, etc.

OxCartMark did a detailed calculation a while back assuming all the steel plate in the barge was of equal thickness, and he got a result of 1" thick all around, so I'd trust that number as being in the right ballpark.

http://forum.nasaspaceflight.com/index.php?topic=36326.msg1341509#msg1341509

By the look of that tear and the possibly wood structure below, I'm wondering if the deck is some type of composite.  One inch steel would have peeled back, not torn; maybe quarter inch plate could tear... And why would you install timbers below decks?

The welding the landing legs/pads to the deck was discussed for an earlier version of the ASDS.  New tie-downs could be because deck is no longer steel.


"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Kabloona

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Quote
By the look of that tear and the possibly wood structure below, I'm wondering if the deck is some type of composite.  One inch steel would have peeled back, not torn; maybe quarter inch plate could tear... And why would you install timbers below decks?

I think it did both "peel" and "tear." It looks from that photo like a big petal of the "peeled down" steel has been cut away. Timbers may have been to support the bent "petal" from below while it was being cut out.


(After peeled steel cut out:)






(Before peeled steel cut out:)
« Last Edit: 03/10/2016 11:10 PM by Kabloona »

Offline OxCartMark

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OxCartMark did a detailed calculation a while back assuming all the steel plate in the barge was of equal thickness, and he got a result of 1" thick all around, so I'd trust that number as being in the right ballpark.

True I did that based on the assumption of uniform thickness of all outer surfaces and ballast partitions and my weight numbers came out exceedingly close to the known weight but afterward someone with fewer assumptions and more naval engineering knowledge (Docmordrid??) came in and convinced us very convincingly that the deck thickness was something else.  1/2"?,  I seem to vaguely recall.  If someone wants to sort through the 300+ pages of ASDS thread 2 they could probably find it.


Anyone know enough about metallurgy to estimate the minimum force required to puncture the steel plating?
That and dry mass would give a lower bound on the velocity at contact.

There are so many problems with trying to do that with normal classroom mechanical engineering knowledge, so many.  You've got strain rate sensitivity (the material's yield strength is higher in a fast hit than in a standard tensile test), you have deformation of the plate into a partial bulge so that even knowing the area of the break you aren't able to multiply that area simply by the shear strength (if it was punched out) or tensile strength (if it was domed and the dome pulled off), and you have the force at the interface of the plate and the rocket being divided between impact (accelerating the plate) and doing work to open the hole.  Also, its not going to happen simultaneously around the perimeter of the hole but rather it would be a sequence of local actions.

I'd guess that the best answer to your question if there is one will come from the military field where I presume there are charts or formulas of projectile size or mass or energy vs. ship hole size.  Perhaps if nobody steps forward with such info we could look around at ships that have been damaged by impacts of known energy (USS Cole comes to mind but probably much thicker steel plate) and work somewhat backward to see what energy and thus speed the stage would have.

Or wait a few more days and see if we can get speed info from the video.

OK, here is a really quick but useless extrapolation to be used for entertainment purposes only:
An online chart of punch press tonnage for these assumptions [1/2" A36 steel, 1" diameter punch] shows an expected punch force of 50 tons.  Assuming the situation of a hole being punched in a machine [all sheared at once, force is proportional to perimeter which is proportional to diameter] then for a 12 foot diameter the force would be 144x 50 tons or 7200 tons, 14.4M lbf, 6M kgf.  Don't take this calculation seriously other than to say you wouldn't want to have your finger between the crashing stage and the deck plate during the event.

Offline matthewkantar

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Six portable welders and a dude.

Steel delivery?

Offline Herb Schaltegger

OxCartMark is correct above that there are MANY variables here. Amusingly, a lot of this kind of analysis parallels the very empirical work performed in the WWII era and earlier by the U.S. Navy Bureau of Ships with regard to armor plate penetration studies using a wide variety of projectiles. The outlines of what's involved in a full analysis of that stuff can be gleaned from reading some of those old BuShips Battle Damage Assessment Reports and books/articles by trivia-obsessed #shipnerds, who spend as much time rehashing the Battle of Jutland as we do parsing ShitElonSays and SpaceX kremlinology - more, actually, since they've been at it for almost a century now.  Google is your friend if you want to dig into that stuff.
Ad astra per aspirin ...

Online launchwatcher

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(USS Cole comes to mind but probably much thicker steel plate)
Not necessarily thicker:

http://www.military.com/Content/MoreContent?file=FL_cole_bradp

Quote
The blast ripped a 40-by-20 foot hole in the Cole's half-inch-thick hull plates below the forward smokestack,


Offline CameronD

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Quote
By the look of that tear and the possibly wood structure below, I'm wondering if the deck is some type of composite.  One inch steel would have peeled back, not torn; maybe quarter inch plate could tear... And why would you install timbers below decks?

I think it did both "peel" and "tear." It looks from that photo like a big petal of the "peeled down" steel has been cut away. Timbers may have been to support the bent "petal" from below while it was being cut out.

There's absolutely no doubt, and never has been, that it's a steel deck.. but let's agree it's approximately 3/4" thick (give or take 1/4") shall we?? :D

The timbers could also be propping up a busted deck beam whilst they get in there and weld it back in place.

It's telling to me that they've pumped out all their ballast tanks - anti-foul (what's left of it) showing all round, spill control boom yet no evidence of hydrocarbon sheen on the water - not something they normally do after target practice.  At first I thought maybe that meant they had a smallish leak, but it's more likely they need the compartment absolutely dry to carry out the repairs and do a close inspection of the hull from inside and want the work-site as level as possible.


Adding: Welding spatter and filings plus salt water = instant rust and is a right PITA to clean up afterwards - and you can't just leave it there either.  Usual practice the world over is to put down hessian sacks or similar and vacuum up afterwards and both of those things are kinda difficult inside a wet compartment.  And that's ignoring the discomfort caused by welding (heat) inside a poorly-ventilated black steel box with condensation running all around (and on!) you whilst you try to strike a spark.
« Last Edit: 03/11/2016 12:28 AM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

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