Author Topic: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2  (Read 2965077 times)

Offline CameronD

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

Online 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." ;) 
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Offline Lar

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6442 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 #6444 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?
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Offline Comga

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6445 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?

Offline meekGee

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Re: SpaceX's Autonomous Spaceport Drone Ship Discussion Thread 2
« Reply #6446 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 #6447 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 #6448 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 #6449 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 #6450 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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