Author Topic: SpaceX Texas launch site Discussion and Updates - Thread 12  (Read 664635 times)

Offline V42

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #40 on: 07/24/2021 06:50 pm »
It looks like most of the speculation was wrong irt direct assembly.  From Mary's photo they are using another jig.  The final level looks like it will only have three columns, with the gap at the built up area from the previous level.

No there are four columns, it's just the the 4th one is a little stubby one (see here) that will probably sit on top of the pulley block which is to be fitted on the taller column at overhang corner of section 8.

They'll either:

- attach this directly on top of that pulley block and then lift that two part assembly up to the aforementioned taller column on section 8 for installation. the rest of section 9 can then be lifted up and everything gets joined together;

or,

- install the stubby column to where it belongs on section 9 while it's on the jig at ground level, the stubby corner will be held in place to the two adjacent corner columns by the 2 horizontal connecting beams, not attached to the jig because it'll be "floating" above that corner of the jig with free air between. Then that gets lifted and joined to section 8.

All this talk (here and elsewhere) about the section 9 configuration ignores one thing… most proposed arrangements do not form a stable geometry for the lift when stacking. No matter how you close out the currently missing fourth corner, the assembly will sag without horizontal members joining the bottom of the corner columns together. But there is also no provision in the corner column gusset plates to attach them in that area. So unless the lifting fixture can provide the needed stiffness, either some kind of temporary bracing will need to be added or there is more to come to section 9 than has been proposed so far.
You can complete the missing diagonals wIth cables, right?  Maybe will need to tension them on final assembly but that's just another come-along.

Unfortunately cables don’t work well in compression ;). But I was mistaken and those temporary horizontal members are indeed there. So my apologies for not looking more careful and raising a nonissue.
Oh come on, you use two, look at any cable stabilized structure out there...

You do understand the concept of preload, right? Of course you can “push” on a preloaded cable as long as you don’t exceed whatever initial tension was in that cable. But a cable has to pull against something in order to preload it in the first place.

If you’re thinking of a simple tower stabilizing guy-wire system, you need at least two for a 2-D planar system and three for a 3-D system.

In a more general sense, you need as many degrees of constraint as rigid body degrees of freedom you are trying to restrain. A non-preloaded cable provides only 1/2 degree of freedom of constraint while a preloaded cable provides a full 1 degree of freedom of constraint.

Offline meekGee

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #41 on: 07/24/2021 08:07 pm »
It looks like most of the speculation was wrong irt direct assembly.  From Mary's photo they are using another jig.  The final level looks like it will only have three columns, with the gap at the built up area from the previous level.

No there are four columns, it's just the the 4th one is a little stubby one (see here) that will probably sit on top of the pulley block which is to be fitted on the taller column at overhang corner of section 8.

They'll either:

- attach this directly on top of that pulley block and then lift that two part assembly up to the aforementioned taller column on section 8 for installation. the rest of section 9 can then be lifted up and everything gets joined together;

or,

- install the stubby column to where it belongs on section 9 while it's on the jig at ground level, the stubby corner will be held in place to the two adjacent corner columns by the 2 horizontal connecting beams, not attached to the jig because it'll be "floating" above that corner of the jig with free air between. Then that gets lifted and joined to section 8.

All this talk (here and elsewhere) about the section 9 configuration ignores one thing… most proposed arrangements do not form a stable geometry for the lift when stacking. No matter how you close out the currently missing fourth corner, the assembly will sag without horizontal members joining the bottom of the corner columns together. But there is also no provision in the corner column gusset plates to attach them in that area. So unless the lifting fixture can provide the needed stiffness, either some kind of temporary bracing will need to be added or there is more to come to section 9 than has been proposed so far.
You can complete the missing diagonals wIth cables, right?  Maybe will need to tension them on final assembly but that's just another come-along.

Unfortunately cables don’t work well in compression ;). But I was mistaken and those temporary horizontal members are indeed there. So my apologies for not looking more careful and raising a nonissue.
Oh come on, you use two, look at any cable stabilized structure out there...

You do understand the concept of preload, right? Of course you can “push” on a preloaded cable as long as you don’t exceed whatever initial tension was in that cable. But a cable has to pull against something in order to preload it in the first place.

If you’re thinking of a simple tower stabilizing guy-wire system, you need at least two for a 2-D planar system and three for a 3-D system.

In a more general sense, you need as many degrees of constraint as rigid body degrees of freedom you are trying to restrain. A non-preloaded cable provides only 1/2 degree of freedom of constraint while a preloaded cable provides a full 1 degree of freedom of constraint.
It's not hard.

If you have a rectangular frame, you can stabilize it with a single diagonal, if the diagonal can take compression without buckling.

Alternatively, two tension-only diagonals (e.g. cables) will also do.
ABCD - Always Be Counting Down

Offline V42

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #42 on: 07/24/2021 09:14 pm »

You do understand the concept of preload, right? Of course you can “push” on a preloaded cable as long as you don’t exceed whatever initial tension was in that cable. But a cable has to pull against something in order to preload it in the first place.

If you’re thinking of a simple tower stabilizing guy-wire system, you need at least two for a 2-D planar system and three for a 3-D system.

In a more general sense, you need as many degrees of constraint as rigid body degrees of freedom you are trying to restrain. A non-preloaded cable provides only 1/2 degree of freedom of constraint while a preloaded cable provides a full 1 degree of freedom of constraint.
It's not hard.

If you have a rectangular frame, you can stabilize it with a single diagonal, if the diagonal can take compression without buckling.

Alternatively, two tension-only diagonals (e.g. cables) will also do.

I fully understand what you’re trying to say, it’s just that it’s not applicable to the specific configuration of the 9th segment. First, we’re talking about tension only members (i.e., cables) so compression capable members (i.e., beams) don’t apply.

Secondly, you’re correct two crisscrossing tension-only diagonals will prevent a simple frame from parallelogramming. But it must be a complete four sided frame, either self forming like a picture frame or effectively become one like a soccer goal post (with its inverted U-shape frame) where the ground forms the fourth side.

But the original post was in regard to the current segment 9 configuration’s need of a horizontal beam connecting the bottom ends of the corner columns to stabilize it when it’s being lifted. With it (as indeed photos show it has been added) nothing else is needed. And if it was not there, running diagonal cables as you suggested would not work. Imagine the soccer goal post example above. Diagonal cables work to stabilize it as long as it’s attached to the ground (synonymous to segment 9 sitting on its assembly jig). But try to lift that goal post off the ground (synonymous to segment 9 lifted off its jig without that lower horizontal brace) and those cable diagonals won’t do the whole job. The vertical side posts (and likewise segment 9’s corner columns) would still be free to move inwards towards each other.
« Last Edit: 07/24/2021 10:18 pm by V42 »

Offline AstroDave

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #43 on: 07/24/2021 10:11 pm »
https://twitter.com/NicAnsuini/status/1419051813043638272

  My guess, a large diagonal piece that goes from one corner of launch tower to other, and supports upper sheave assembly.

First image, from Starship Gazer, is upper sheave assembly that would tie into four eyes on underside of grey structural piece.

Second image, from Ocean Cam, is lower sheave assembly that would be connected to lifting/catching structure.

Offline alugobi

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #44 on: 07/24/2021 10:36 pm »
They are not going to use cables, so please take that sidetrack elsewhere.


Online pyromatter

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #46 on: 07/24/2021 11:02 pm »

Offline AstroDave

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #47 on: 07/24/2021 11:05 pm »
  First image shows two 8 hole flanges on tower segment opposite stubby tower, from bocachicagal's image (_DSC9639 (2).JPG) from BC Production Update thread.

  Second image shows 8 holes drilled in I-Beams of newly delivered structural piece, image from Nic Ansuini.

  Third image is a hack job of photo editing showing my take on where this piece will be placed within tower section #9. Image of upper sheave support is screen shot from Ocean Cam video in BC Production Update thread.

Edit: Damn! Time it took to review some images to attempt a hack photo edit, and tower team already has it in place. This is going to be sweet to see in final form.
« Last Edit: 07/24/2021 11:14 pm by AstroDave »

Offline alugobi

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #48 on: 07/24/2021 11:31 pm »
Quote
The drawworks and cable spooler/drum around the adjacent corner of the tower's base says otherwise.
That's a given.  Those other two were debating the fine points of how to make a girder structure that wasn't what we could see happening in the pictures, hence a sidetrack.

Offline baking

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #49 on: 07/25/2021 02:26 am »
The thumbnail from this "SpaceX Pink" video is credited to @Bl3D_Eccentric although I can't find the original:



I just want to point out that he calculated the lengths of the partial columns well enough to know that there would be a gap there, which has just been filled with the new diagonal beam/sheave support.  Good work!

Offline DreamyPickle

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #50 on: 07/25/2021 11:13 am »
The pictures from the side can be a confusing. It seems that the segment being built right now only has three "legs" and that the new component that was just mounted goes directly through where the fourth leg will be. Once lifted it will go directly over the existing "nose". I also has large holes at the end to mount some sort of pulley.

It's fixed in place and quite short so this can't be used as a crane. Instead it seems likely that a set of cables will pass through the nose and connect to a section below that slides on rails at variable height.

Offline VaBlue

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #51 on: 07/25/2021 01:02 pm »
It's fixed in place and quite short so this can't be used as a crane. Instead it seems likely that a set of cables will pass through the nose and connect to a section below that slides on rails at variable height.

Yeah, I've been wondering what people have been calling a crane.  Since the ~40' tall foundation was poured for the tower, there's been zero evidence of any tower type crane going through the middle of the it.  I have to wonder if they're calling the Drawworks system to lift the catching/stabilization arms a 'crane'?  That's the only thing I can think of...  At this point, it seems pretty clear how those arms will move up and down.

The question I have now is how do they move laterally?  Or do they?

Offline DreamyPickle

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #52 on: 07/25/2021 02:50 pm »
Are there any other examples of a tower with a vertically sliding carriage like SpaceX appears to be building?

I can't think of any launch tower arm that was not firmly fixed to the tower itself.

This adds a lot of complexity and the only good reason to go for sliding arms is in order to dampen the shock of a booster being caught.

Offline grndkntrl

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #53 on: 07/25/2021 03:00 pm »
Are there any other examples of a tower with a vertically sliding carriage like SpaceX appears to be building?

I can't think of any launch tower arm that was not firmly fixed to the tower itself.

This adds a lot of complexity and the only good reason to go for sliding arms is in order to dampen the shock of a booster being caught.

Yes, the vertical drop rides at amusement parks have a basically similar method of operation. Though at a much smaller scale of course, and without arms extending from the seating platform.



edit: there's also the tower at the second launch pad of the ISRO's Satish Dhawan Space Centre, but that's only about a third the height of the tower at Boca Chica, however it is much more complex with the number of arms, gantries, and other things it has going on, albeit it doesn't have to catch anything.



You could also compare it to the basic principle of the lifting mechanism on a forklift truck and/or stackers.

There are lots of reasons why they went with the multipurpose arms on a carriage approach, all of which have been discussed here extensively.

It's actually not really that complex at all when you really think about it.
« Last Edit: 07/25/2021 06:51 pm by grndkntrl »

Offline beentheredengthat

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #54 on: 07/25/2021 04:11 pm »
.

You could also compare it to the basic principle of the lifting mechanism on a forklift truck and/or stackers.

There are lots of reasons why they went with the multipurpose arms on a carriage approach, all of which have been discussed here extensively.

It's actually not really that complex at all when you really think about it.

Yes! I knew this reminded me of something

« Last Edit: 07/25/2021 04:12 pm by beentheredengthat »

Offline edzieba

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #55 on: 07/25/2021 04:20 pm »

Swing-jig crane? Pivot at the 'back' corner, extends over the shortened 'front' corner near the launch table. The corner doesn't point directly at the launch table (rotated slightly counter-clockwise) so the jib only needs a relative small angle of swing to be able to move from directly above the launch table to sufficiently far off to clear the legs. Roll SPMT next to launch table, swing jib over, lift vehicle, swing jib over table, lower vehicle.
Simple, and unlike the grabber-arms it's a practically off-the-shelf system, which means it can be implemented fast.

Offline DreamyPickle

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #56 on: 07/25/2021 04:25 pm »
Swing-jig crane? Pivot at the 'back' corner, extends over the shortened 'front' corner near the launch table. The corner doesn't point directly at the launch table (rotated slightly counter-clockwise) so the jib only needs a relative small angle of swing to be able to move from directly above the launch table to sufficiently far off to clear the legs. Roll SPMT next to launch table, swing jib over, lift vehicle, swing jib over table, lower vehicle.
Simple, and unlike the grabber-arms it's a practically off-the-shelf system, which means it can be implemented fast.
There are some pictures which show bolt holes on this new "arm" as well as on the rearmost pillar. This means it's fixed in place.

Offline grndkntrl

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #57 on: 07/25/2021 04:37 pm »
Swing-jig crane? Pivot at the 'back' corner, extends over the shortened 'front' corner near the launch table. The corner doesn't point directly at the launch table (rotated slightly counter-clockwise) so the jib only needs a relative small angle of swing to be able to move from directly above the launch table to sufficiently far off to clear the legs. Roll SPMT next to launch table, swing jib over, lift vehicle, swing jib over table, lower vehicle.
Simple, and unlike the grabber-arms it's a practically off-the-shelf system, which means it can be implemented fast.

People really need to let go of the idea of a movable crane boom/jib on top of the tower with a hook swinging around on the end of a cable.

That ship sailed, sunk, and is long dead in the water!

Offline DreamyPickle

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #58 on: 07/25/2021 05:00 pm »
It's still not clear to me how they're going to stack StarShip without a movable crane at the top of the tower.

They need to lift it 100 meters into the air and then integrate it with the separation mechanism on the booster. ​How would you do this with movable arms? The starship so far has only been moved by hooking the nose. Are they going to add new lifting points around the "waist" of the vehicle? The wing surfaces don't look anywhere strong enough to hold the whole vehicle.

It would make sense for integration between the booster and starship to be performed on a platform that can hold workers and also fueling connections. Does this mean the tower will have two movable carriages?

It's also much easier to design arms that only need to close around a single axis going through the center of the launch table. I saw a render with arms that can both close and rotate but that seems very complicated.

The most likely solution at this point seems to be to keep the FrankenCrane around and use that for all lifts that require horizontal movement.

Offline grndkntrl

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Re: SpaceX Texas launch site Discussion and Updates - Thread 12
« Reply #59 on: 07/25/2021 06:32 pm »
It's still not clear to me how they're going to stack StarShip without a movable crane at the top of the tower.

They need to lift it 100 meters into the air and then integrate it with the separation mechanism on the booster. ​How would you do this with movable arms? The starship so far has only been moved by hooking the nose. Are they going to add new lifting points around the "waist" of the vehicle? The wing surfaces don't look anywhere strong enough to hold the whole vehicle.

It's really quite simple.

Either they pick Starship up at the existing nose lifting points, using captive grapplers built directly into the arm/s, or they pick up an adapter in the arms "grip" (if this will be a thing) and this then slips over the nose and grabs onto the lifting points, again using captive grapplers.

or

The arms slip under the forward flaps and lift it from there. This would likely require some sort of crush protection for the TPS tiles in that area and perhaps additional reinforcement too, or there may be some sort of recessed attachment point just like on the nose, which is protected during reentry by a small TPS tiled access hatch that can be opened & closed remotely without having to have someone physically access it.

I'd go with the existing nose attachment points as it's worked well so far.

It would make sense for integration between the booster and starship to be performed on a platform that can hold workers and also fueling connections. Does this mean the tower will have two movable carriages?

Remember that one of the goals is orbital refueling, so they absolutely will have to be able to make fuelling connections without any personnel involved.

The propellant filling point on Starship is under the skirt, not on the outside, and it'll be filled through a mating connector on the top of the booster - either once the booster is already filled so it can support Starship when stacked on top; or at the same time they are stacked together, with the arms taking some of the load of starship off of the booster.

I suspect that the currently under construction booster thrust/Max-Q simulator, dubbed by some as the "can crusher", might also be used to test whether a booster really can support the weight of starship in both of the above scenarios at various filling stages.

Elon has also said: https://twitter.com/elonmusk/status/1372697001633136646

So yes it's also feasible for the auxiliary interstage stabilisation arm/s to have a work platform or walkway, in order to to allow ground crew to work safely. These could be on the same carriage structure as the main arms, or perhaps on a lower carriage which can be moved independently of the one on which the main arms are mounted.

It's also much easier to design arms that only need to close around a single axis going through the center of the launch table. I saw a render with arms that can both close and rotate but that seems very complicated.

I'll refer you to Elon himself for that answer:

https://twitter.com/elonmusk/status/1314113154696310784

https://twitter.com/elonmusk/status/1330201798490120193

The most likely solution at this point seems to be to keep the FrankenCrane around and use that for all lifts that require horizontal movement.

If they've not completed all of the arms necessary structure by the time it comes to attempt the first orbital launch, then yes this is possible as the LR11000 has a mention of this secondary purpose in its FAA obstruction evaluation study report:

Quote
Crawler Crane to support SpaceX orbital launch site construction and launch operations. Note: 450ft structure height is when the crane is at its highest boom angle and will most frequently be at a height of 350ft.

while the OES report for Frankencrane (the LR11350) does not mention launch operations:

Quote
Crawler Crane to be unsed in the construction of new SpaceX launch tower.

In the long term a crane is not going to be conducive to rapid reuse turnaround times.

The multipurpose arms are, and the pace of construction on them would suggest that it will happen sooner rather than later.

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