Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2  (Read 2965156 times)

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6420 on: 03/09/2016 03:27 pm »
Was that the first time ever that three engines were fired in flight in the atmosphere?
  F9R dev / GH2.  Didn't that thing have one good flight on 3 and a second flight on 3 that ended somewhat like what we have here?
_______

The characters yelling "a tin can hitting a steel deck - nothing to worry about!" obviously had never heard of a space shuttle named Columbia: "Piece of foam hitting an RCC panel - nothing to worry about!".
I'd bet everyone here has heard that news.  And its got nothing to do with this situation.  RCC is near the far end of the brittle-ductile spectrum.  Mild steel is also near the far end of the brittle-ductile spectrum.  Its just that they're at opposite ends. And the stage is limited in its speed by air drag to something in the turboprop speed range, and less for every moment of engine firing.  1/2MV^2
_______

For those arguing they will not be releasing the video, I most definitely don't see any reason why they wouldn't !
Have my doubts about if we'll be graced by a video. Think it'll be at most pics and a few tweets.
This was not the most videonegative comment that has been posted but only the most videonegative sentament I found in a quick search.  I've seen comments stating that its quite unlikely that we'll see video on four previous occasions.  All have been fully incorrect.  I'm betting on video here as well.  Praise be unto Elon!

_______

We have it on good authority what the terminal velocity is near seal level.  I have a number in mind but I'm not sure and I don't recall if its L2 or not.  I came across the authoritative post again ~2 weeks ago but didn't think to make a good mental note or bookmark of it.  Since it is relevant to the situation here does anyone have it?

_______

On the theory of the octaweb having punched through the deck and is currently stowed below deck... My initial thought was that the hole is too small for that but looking back at the overhead image I've gotta say yes.  Its round and the diameter is the same as the diameter of the large ?interstage? on deck.  But I wouldn't expect it to look like much, the damage ratio between what the barge deck has suffered to what the octaweb has suffered might be in the triple digits.  It would take the NTSB working with dental records and DNA to make sense of it.  I don't know how TEA behaves when dunked in water very quickly but I suppose there is some chance that it may be in that mess and still active and if so might slow down repair efforts. 

I've gotta imagine that when you take big turbopumps running at what, 30,000 rpm and run them into 1/2" steel plate at that kind of speed its gotta be dramatic.

We know from previous kabooms that the pressure in the tanks causes the tank skin to go radially outward and the upper end of the tank to depart axially away from the engines. If it hit vertically engines first then the top of the tank and interstage would go more or less up relative to a reference frame on the stage.  But (and this is unimportant other than for the visual musing in my head) would it go up relative to to a stationary reference or just continue down more slowly or something in between.  I hope the video framing is wide enough to show the top.  The big kick for me would be if the bottom of the stage slammed into the barge but the top was more or less decelerated to zero speed before falling to the deck.
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Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6421 on: 03/09/2016 04:19 pm »
Does anyone have knowledge on what the legal and / or certification hoops are that barge repairs may need to go through before CRS-8?  CG?  Naval engineers?  Re-survey?  I don't know what I'm talking about here but my guess is that this step if it is necessary could take longer than it takes to buff out the scratches.

edit: Looks like the good folks of Elsbeth III might be out shopping or having lunch or somesuch.
« Last Edit: 03/09/2016 04:30 pm by OxCartMark »
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Offline meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6422 on: 03/09/2016 04:32 pm »
The diameter should correspond to the octaweb sans engine bells, and that's about what we see.
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Offline cscott

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6423 on: 03/09/2016 04:39 pm »
We've had various discussions of recertification on this thread but my recollection is that we've never actually "caught SpaceX in the act" when it comes to the required inspection cruises, etc.  The official coast guard records seem to be filed on an extreme temporal delay, so we can't easily match up the paperwork with the barge-stalking.  But we've never heard of an ASDS outing delayed for paperwork; seems they've got a good relationship with whoever's doing the inspections.

In my not-very-well-informed opinion, I think the ASDS will be ready for CRS-8 *unless* there is long-lead-time damage to the thrust masters.  Not that it won't keep folks very busy in the interim.  Possibly they could "borrow" bits of JRtI if needed... I'm thinking electronic gear inside the containers mostly.  But everything is containerized, and assuming they can get the thrustmasters working everything else could be shipped over from long beach and welded to the deck in thirty days no problem.

Again... I am not a naval architect, I'm just basing this on how long previous outfittings of JRtI and OCISLY seem to have taken, based on our visual stalking.  There may well be not-visibly-obvious work to be done (like the paperwork you mention) that could hold things up.

Offline cambrianera

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6424 on: 03/09/2016 04:47 pm »

We have it on good authority what the terminal velocity is near seal level.  I have a number in mind but I'm not sure and I don't recall if its L2 or not.  I came across the authoritative post again ~2 weeks ago but didn't think to make a good mental note or bookmark of it.  Since it is relevant to the situation here does anyone have it?


First landing discussion, hrissan analisys: "Terminal velocity before landing burn is about 150 m/sec."
http://forum.nasaspaceflight.com/index.php?topic=39100.msg1465116#msg1465116
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Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6425 on: 03/09/2016 05:31 pm »
That's some pretty solid work.  But wasn't there also a statement from SpaceX or Elon on terminal velocity?
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Offline rsnellen4

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6426 on: 03/09/2016 05:59 pm »
Assuming that the Falcon 9 was vertical, the first substantial structure (not counting legs and engine bells) would be the center engine combustion chamber, followed by the 8 outer engine chambers, and THEN the octoweb structure.  The first could spike through the deck pretty easily, the second might widen the hole a bit, but the octoweb would probably arrest the penetration if it doesn't come apart after the powerheads come through the bottom of the fuel tank...

Offline CyndyC

That's some pretty solid work.  But wasn't there also a statement from SpaceX or Elon on terminal velocity?

Can we be confident the re-entry burn plus drag slowed the stage to a usual terminal velocity? Not clear why you're asking for this particular landing attempt. I've only read Elon Musk mention the usual planned speed at touchdown to be 2m/s or about 4.47mph.
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Offline cscott

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6428 on: 03/09/2016 06:08 pm »
Yes.  We can be confident the stage was at terminal velocity.  Even meteors end up at terminal velocity, and they are (a)  starting out at earth escape velocity, and (b) considerably less fluffy.

Offline CyndyC

The previous posts inspired me to put the images below together, and in the process I noticed an ideal clue to the size of the hole not too far behind it -- an 8-rung ladder, the length of which would equal 8ft from floor to top when folded. When the ladder length measures exactly 5/8" onscreen, the widest distance across the hole measures 17/16", so that hole is about 13.6ft across, about 1.5ft wider than stage 1. My visual impression is the engine bells do not exceed the diameter of the stage. Please don't hold me to the lawn dart approach theory, I'm somewhere between that and vertical, but the image I chose to overlay seemed appropriate enough for now, credit to a Tom Bozsoky.

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Offline meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6430 on: 03/09/2016 07:23 pm »
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Offline thor1872

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« Last Edit: 03/09/2016 08:20 pm by thor1872 »

Offline cstrahan

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6432 on: 03/09/2016 08:36 pm »
Just happened to arrive in Cocoa today and took the attached pic from across the harbor. I talked with a woman who had been staking out the barge most of the afternoon - she reported that they had been pumping water from both left and right sides earlier - now just left.

She said there were lots of folks on deck but a lot of talking and standing around. One nicely dressed person shaking hands.

Not much removal or cleanup activity that she could see.

Offline Rocket Science

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6433 on: 03/09/2016 08:41 pm »
Just happened to arrive in Cocoa today and took the attached pic from across the harbor. I talked with a woman who had been staking out the barge most of the afternoon - she reported that they had been pumping water from both left and right sides earlier - now just left.

She said there were lots of folks on deck but a lot of talking and standing around. One nicely dressed person shaking hands.

Not much removal or cleanup activity that she could see.
Welcome to the forum! :) Great pic and firsthand report thank you! 8)
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Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6434 on: 03/09/2016 08:43 pm »
Good stuff, Cindy.

That's more ASDS than I think I've ever seen.  It would be nice if someone could get a pic of the draft marks on the sides.  IIRC, it drafts 3 feet with no ballast (?). So I conclude there is a hole in the bottom.  Could be that large areas of bottom plate need to be removed and replaced.  Could be that there's only a small hole and much of the raising is to help (initially at least) in retriving the scrap metal in the compartment.  There would seem to be no reasonable way to raise that area out of the water for servicing so either they weld it underwater style or they go to a drydock (where?) or (extreme) they do some crazy ballasting maneuver that sinks or depresses the other end and projects the troubled end into the air.  The latter seems very improbable given that the equipment at the bow would need to be removed for that.  Hmm, or maybe if it needs to be raised they sink some barges under it and then raise it on them.

Looking back at Marek's super resolution pictures and the Ken Burns slowmo video you can see a green trailer mounted pump on the deck.
________

Just happened to arrive in Cocoa today and took the attached pic from across the harbor.
It appears to my eyes as if the large tarped section, the presumed interstage, is no longer on deck.
________

Hey, did anyone think of this scenario - the stage was coming down at terminal velocity and the multiple engine burn was commanded but the engines were so damaged (for instance, cooling jackets burned through by re-entry) that all they got was an open fire at the bottom but no appreciable thrust / deceleration.  That unlikely scenario would give the bright ball of light we saw in the video along with a hard hit.  Counter argument - unless at least one engine were burning properly it would be unlikely that the video link would have been interrupted.

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« Last Edit: 03/09/2016 08:49 pm by OxCartMark »
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Offline meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6435 on: 03/09/2016 10:16 pm »
Eeyup.

Wrt to speed, how many video frames show the plume?  We should be able to tell the difference between  25 m/s and 250...
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Offline the_other_Doug

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6436 on: 03/09/2016 10:17 pm »
Hey, did anyone think of this scenario - the stage was coming down at terminal velocity and the multiple engine burn was commanded but the engines were so damaged (for instance, cooling jackets burned through by re-entry) that all they got was an open fire at the bottom but no appreciable thrust / deceleration.  That unlikely scenario would give the bright ball of light we saw in the video along with a hard hit.  Counter argument - unless at least one engine were burning properly it would be unlikely that the video link would have been interrupted.

The counter-argument is only valid if we assume that the video feed was interrupted before the impact, and not by the impact.  If the broadcast system buffers a second or two of the video, that buffer showing the last second or so before the blast could simply have been lost, and the feed wasn't affected by a problematic plume and its acoustic energy.

My own thinking is that one or more of the engines failed to light or come up to thrust during the three-engine landing burn.  Think of it like this -- the only way a three-engine burn makes sense is by bringing three engines to full thrust for just a few seconds, at a very low altitude (like less than a km) to brake from terminal velocity to zero.  If it was possible to do a hoverslam and save fuel by doing a late, low-altitude single-engine burn at up to full thrust, they could have done that -- and I imagine that would use less fuel than starting up three engines.  Three engines means you need more thrust than one engine, at full thrust, could provide, I would think.  (So, okay, the three engines would have to amount to at least a little more braking than a singe engine at full thrust could provide, but not all three would have to fire at full thrust.  Each engine would have to run at a throttle of about 40% to give you more thrust than a single engine at full thrust, and we don't have enough info on the landing profile to know how much more was needed.  Maybe they really did need to run all three at full thrust.)

With that kind of maneuver, you need to slow down really fast with really small margins in terms of altitude.  Going roughly 150 m/s at terminal velocity, if you start up your engines at 750 meters and they don't start up, you hit the deck five seconds later...
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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6438 on: 03/09/2016 10:38 pm »
Good stuff, Cindy.

That's more ASDS than I think I've ever seen.  It would be nice if someone could get a pic of the draft marks on the sides.  IIRC, it drafts 3 feet with no ballast (?). So I conclude there is a hole in the bottom.  Could be that large areas of bottom plate need to be removed and replaced.  Could be that there's only a small hole and much of the raising is to help (initially at least) in retriving the scrap metal in the compartment.  There would seem to be no reasonable way to raise that area out of the water for servicing so either they weld it underwater style or they go to a drydock (where?) or (extreme) they do some crazy ballasting maneuver that sinks or depresses the other end and projects the troubled end into the air.  The latter seems very improbable given that the equipment at the bow would need to be removed for that.  Hmm, or maybe if it needs to be raised they sink some barges under it and then raise it on them.

Looking back at Marek's super resolution pictures and the Ken Burns slowmo video you can see a green trailer mounted pump on the deck.

The hole appears to be right over one of the ballast water tanks, so the pumping was most likely removing ballast water (and the copious quantities from the deck flooding that would have gone down the hole also) so they can get down there, tidy up, and take a look.  They're sure to have had divers down already, so they'd already know what they're up against.  In any case it sure doesn't look like it's sinking any time soon.
 
The only way we'll know if there's underwater damage is if they move the ASDS to a dry-dock or commercial slip-way somewhere nearby, because in my experience there's no other way (by ballasting, etc.) they could access that area whilst in the water.  ..but from all we know at this point, I'd suggest that if indeed there is a hole in the bottom at all (a dent more likely) it's a small one because the ribs that brace the bottom plating would have absorbed whatever impact force was left by whichever bit made the hole in the deck.

Of interest to me is the lack of scorch marks on anything around the hole - even the thruster in shot looks brand new.   Perhaps, as Doug says, they did have issues with re-lighting the engines after all...

But if it's the octaweb that made that hole, why were they so far off-target?
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Offline TomTX

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6439 on: 03/09/2016 10:43 pm »

But if it's the octaweb that made that hole, why were they so far off-target?

Easy answer is that they ran out of usable fuel partway through the last course correction.

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