Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2  (Read 2406246 times)

Offline cstrahan

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6440 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 #6441 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 #6442 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.

Shades of

Forget shades, it was this:
« Last Edit: 03/09/2016 08:49 PM by OxCartMark »

Online meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6443 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 #6444 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...
-Doug  (With my shield, not yet upon it)

Offline thor1872

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Offline CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6446 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?
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.

Offline TomTX

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6447 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.

Offline CameronD

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6448 on: 03/09/2016 10:45 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.

Only trouble with that answer is that the fins run on nitrogen gas hydraulic fluid..
« Last Edit: 03/09/2016 11:16 PM 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.

Offline Herb Schaltegger

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) ...


As I wrote last night, "explains the list." ;) 
Ad astra per aspirin ...

Offline Lar

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6450 on: 03/09/2016 10:50 PM »
Only trouble with that answer is that the fins run on nitrogen gas..
I don't believe that's correct, they use an open loop hydraulic system, IIRC
"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
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Offline Wolfram66


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.

Only trouble with that answer is that the fins run on nitrogen gas..

CameronD: The GridFins run on hydraulic fluid, not N2. N2 cold gas thrusters are used for nudges and maneuvering outside the atmosphere . GridFins use open hydraulic system which dumps into Merlin engine fuel cycle.

Offline OxCartMark

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6452 on: 03/09/2016 11:06 PM »
New picture

Which implausiates my earlier conjecture that the center of the deck also has damage (none) and confirms that the interstage has been removed.

Please, anyone else that is going there to get us pictures please borrow Marek's camera which is a camera that thorougly doesn't suck.  New NSF rule: All non-drone ASDS pictures on the east coast to be taken with Marek's camera, all non-drone ASDS pictures on the west coast to be taken with Helodriver's camera.
__________

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.

No.  Three engines for a short time uses less fuel than one engine for a longer time.  The speed at the beginning of the burn is nearly the same at either the one engine start height or the three engine height but starting them later with higher acceleration means less time that gravity is soaking up your engine burn delta v.  Or in other words hovering eats fuel.  More slam and less hover eats less fuel.  (Punching through the deck can be done with as little as no fuel consumption)

_________

Regarding the discussion about nitrogen gas, it seems as if all of the comments are slightly off.  The grid fins are powered directly by an open loop hydraulic system which in turn is powered by high pressure hydraulic fluid which is stored in an accumulator type situation under nitrogen gas.  Without nitrogen pressure or hydraulic fluid there can be no movement of the grid fins.  But once the engines are fired up their control authority far exceeds that of the grid fins.  And that is particularly true a few seconds into the burn as air speed is reduced.
________

Elsbeth III remains on the south side of the channel.  My theory is that they've been out to sea for 3 weeks or so and once they came into port they had work to do to get back to ship shape.  Now tonight they're going to tie up near the bars where everyone can go out and have a good time and easily stumble their way back to the ship.
________

Here is what I was trying to find earlier.  Near proof that Marmac 300 series barges are rediculously stout.  http://www.dredgemag.com/March-April-2003/Titan-Lifts-4000-ton-Wreck/
________

Can I have my video now?

Online Comga

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6453 on: 03/09/2016 11:13 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.

Only trouble with that answer is that the fins run on nitrogen gas..

CameronD: The GridFins run on hydraulic fluid, not N2. N2 cold gas thrusters are used for nudges and maneuvering outside the atmosphere . GridFins use open hydraulic system which dumps into Merlin engine fuel cycle.

{bold emphasis mine}
I don't believe that we know that and strongly suspect that it is wrong.
The regenerative coolant is fuel that is dumped into the Merlin engine combustion chamber.
The fuel is, or at least was, also used as hydraulic fluid, but the systems are separate.  One is above the tanks (grid fins) the other is below the tanks (engines and bells.)
edit: The grid fins' hydraulic fluid is either collected in a tank or dumped overboard.
« Last Edit: 03/09/2016 11:14 PM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6454 on: 03/09/2016 11:48 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.
The fins can't help at low velocity.  The last bit of maneuvering is mostly engine.

The fins are for "passive" aero control between the reentry burn and the landing burn.

If the landing burn was interrupted (out of fuel, bad relight, etc) then this is what we'll see.

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.

Only trouble with that answer is that the fins run on nitrogen gas hydraulic fluid..
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Offline Space Ghost 1962

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6455 on: 03/10/2016 12:04 AM »
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.

Thank you for the nomination of most negative, but I must decline the honor, as on the field of SX negativity, there is no way I can hold a candle to either Ed Kyle or Jim in that regard - they both beat me cold. ;)

As to "why", suggest that Shotwell's remarks as to failures being hard to immediately diagnose is more the reason, even though her remark was aimed at "launch failures" in general, it applies here even more.

Suggest further that a lot is happening on this recovery that is "new", and that it may take a while to digest the implications of all of the compromises necessary to accomplish the return. By the time they have it "figured out", there will have been other recoveries "flown" and no one will be interested in the stale, "not newsworthy" SES-9 one. So it may be a footnote, and eventually added into the "blooper reel" without much remark.

It may surface again later when next they try a "zero boost back" recovery, as an aside of what they needed to know to make another like attempt.

Which would be unfortunate for those of us who'd like more hints "sooner", but entirely reasonable as it's their proprietary flight test, and for professionalism - they'd like to say something when they know something for sure.

edit: correction - Jim thinks this unfair
« Last Edit: 03/10/2016 12:46 AM by Space Ghost 1962 »

Offline Jim

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6456 on: 03/10/2016 12:30 AM »

Thank you for the nomination of most negative, but I must decline the honor, as on the field of SX negativity, there is no way I can hold a candle to either Ed Kyle or Jim in that regard - they both beat me cold. ;)



Since when is being evenhanded or skeptical counted as being negative. 

Offline cscott

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6457 on: 03/10/2016 12:37 AM »

Thank you for the nomination of most negative, but I must decline the honor, as on the field of SX negativity, there is no way I can hold a candle to either Ed Kyle or Jim in that regard - they both beat me cold. ;)



Since when is being evenhanded or skeptical counted as being negative.
Out of curiosity: do you think we'll see video from this landing attempt, Jim?

Offline Space Ghost 1962

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6458 on: 03/10/2016 12:47 AM »

Thank you for the nomination of most negative, but I must decline the honor, as on the field of SX negativity, there is no way I can hold a candle to either Ed Kyle or Jim in that regard - they both beat me cold. ;)



Since when is being evenhanded or skeptical counted as being negative.

My apologies - is the correction to your liking?

Offline Chris Bergin

Ok, Thread 3 time. Let me set it up.

Thread 3:
http://forum.nasaspaceflight.com/index.php?topic=39766.0
« Last Edit: 03/10/2016 01:02 AM by Chris Bergin »

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