Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 386515 times)

Online matthewkantar

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #400 on: 12/20/2017 02:54 PM »
Nice detail.

Online StevenV

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #401 on: 12/20/2017 03:00 PM »
The center core also has no use for the greater cross-range the titanium fins give.

Offline russianhalo117

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #402 on: 12/20/2017 03:16 PM »
I wonder if they are production-constrained on the Ti fins?  It was discussed here (tea-leaf-reading on some ambiguous tweets from Elon) that perhaps the first prototype Ti fins were machined from a solid block while the production fins would be forged, and that the forging process had significant setup costs/lead time, so they might not want to get that going until the Ti fin design had been thoroughly vetted... presumably including on this FH maiden flight.

So there might be only two sets of prototype Ti fins in existence, and they've been dedicated to the two FH side boosters... explaining why some other recent high-energy F9 flight candidates haven't opted for Ti.

For that matter, they obviously see no reason *not* to use Al fins, like on the center booster here, so Al not be end-of-lifed with F9 block 5.  Put another way, the only "problem" with Al fins is limited reusability, not functionality (for F9; FH needs the extra control).
They may 3D print the fins in the future if they want to pursue maximum achievable strength, quality, reduced lead and manpower times and cost reduction.
« Last Edit: 12/20/2017 05:35 PM by russianhalo117 »

Online nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #403 on: 12/20/2017 03:19 PM »
It has been mentioned by Elon they they will be forged. The biggest Ti forgings ever.

Offline cscott

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #404 on: 12/20/2017 03:25 PM »
Elon has tweeted forged as well as machined at various times.  (He's never mentioned printed.) Let's please not reopen that debate.

Online ugordan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #405 on: 12/20/2017 03:29 PM »
I just noticed that the white gunk/residue inside the nozzles actually contains markings on some engines. The right side booster has two nozzles marked "6" and "8", although that would make them clocked the opposite way of what the F9 user guide shows. The left side booster also appears to contain the number 8 in the expected location, considering the two cores are 180 deg apart.

Edit: nvm, it's the same clockwise direction.
« Last Edit: 12/20/2017 03:32 PM by ugordan »

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #406 on: 12/20/2017 03:44 PM »
Larger versions

Note that the overhead view was photoshopped, a composite of at least two frames, possibly 3. The interstage is too short and it's missing the obvious stage separation pusher that's visible above the FH logo in the other shot.

I guess they couldn't capture the entire vehicle from overhead in a single frame without gross fisheye distortion so they had to mosaic separate frames with significantly different perspective.

Anyway, nice to finally see the mated hardware, the cores are actually a bit closer together than I imagined them to be due to the leg spacing, etc.

Not to mention that operator looking up (twice), next to the yellow command cord...
« Last Edit: 12/20/2017 03:44 PM by meekGee »
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Online pb2000

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #407 on: 12/20/2017 05:11 PM »
I'm sure this has been asked multiple times in the past, but what's with the strap holding up the center engines? I've seen it before on recovered cores being transferred back to the HIF, but not during rollout prep.
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Online matthewkantar

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #408 on: 12/20/2017 05:28 PM »
I'm sure this has been asked multiple times in the past, but what's with the strap holding up the center engines? I've seen it before on recovered cores being transferred back to the HIF, but not during rollout prep.

Just a guess: the center engine may have a different gimbal than the outsiders, needs a little help to stabilize it while moving. For instance the outside engines are more accessible, or more easily lockable than the center.

Matthew

Offline the_other_Doug

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #409 on: 12/20/2017 05:33 PM »
I have a question about the upper attach structure.  I doubt we will know for certain how it is planned to work until we see the flight, but here goes:

In the detail below, it would appear that the cross-struts that attach tangentially across the center core cannot remain on the center core -- at least where they are right now -- and still allow its grid fins to deploy and have full freedom of movement.  But I would suspect the same thing of the side cores, were these struts to separate in the middle and depart with the side cores.

Do they actually fold up along the side of the interstage on the center core?  Do they stay with the side cores, giving them uneven airflow and thus requiring the additional control authority of the larger titanium grid fins?  Or are they simply jettisoned at some point, a small amount of hardware given up to the rocket equation gods?

Sorry if this has been discussed in detail elsewhere and I have missed it.  It's not humanly possible to read every post in this forum and still maintain heavy life responsibilities... sigh...
-Doug  (With my shield, not yet upon it)

Online Johnnyhinbos

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #410 on: 12/20/2017 05:36 PM »
I have a question about the upper attach structure.  I doubt we will know for certain how it is planned to work until we see the flight, but here goes:

In the detail below, it would appear that the cross-struts that attach tangentially across the center core cannot remain on the center core -- at least where they are right now -- and still allow its grid fins to deploy and have full freedom of movement.  But I would suspect the same thing of the side cores, were these struts to separate in the middle and depart with the side cores.

Do they actually fold up along the side of the interstage on the center core?  Do they stay with the side cores, giving them uneven airflow and thus requiring the additional control authority of the larger titanium grid fins?  Or are they simply jettisoned at some point, a small amount of hardware given up to the rocket equation gods?

Sorry if this has been discussed in detail elsewhere and I have missed it.  It's not humanly possible to read every post in this forum and still maintain heavy life responsibilities... sigh...
They fold up per the animation
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Online Lar

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #411 on: 12/20/2017 05:40 PM »
I have a question about the upper attach structure.  I doubt we will know for certain how it is planned to work until we see the flight, but here goes:

In the detail below, it would appear that the cross-struts that attach tangentially across the center core cannot remain on the center core -- at least where they are right now -- and still allow its grid fins to deploy and have full freedom of movement.  But I would suspect the same thing of the side cores, were these struts to separate in the middle and depart with the side cores.

Do they actually fold up along the side of the interstage on the center core?  Do they stay with the side cores, giving them uneven airflow and thus requiring the additional control authority of the larger titanium grid fins?  Or are they simply jettisoned at some point, a small amount of hardware given up to the rocket equation gods?

Sorry if this has been discussed in detail elsewhere and I have missed it.  It's not humanly possible to read every post in this forum and still maintain heavy life responsibilities... sigh...

I seem to recall seeing the answer to this but I can't recall where. So this is phrased as a guess. I am guessing that the two arms remain attached to the center stage. They pivot downward at hinge points that are not very far from the center point of the center core. This pivot gives the clearance necessary for the center stage grid fins to do their thing. Since they stay attached to the center stage, they have no effect on the side core grid fins post separation.
« Last Edit: 12/20/2017 05:43 PM by Lar »
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Online nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #412 on: 12/20/2017 05:45 PM »
They remain on the center core and pivot upward. You can see the latches just above the US flag.

« Last Edit: 12/20/2017 05:48 PM by nacnud »

Offline the_other_Doug

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #413 on: 12/20/2017 05:55 PM »
They remain on the center core and pivot upward. You can see the latches just above the US flag.

Thanks.  I thought those lumps up on the interstage looked like latch points.  And yeah, I recall what the original CGI showed, but the SpaceX CGIs have not always been accurate, especially after several intervening years of design-fiddling.

I will be quite impressed with a strut system that has a hinge right where it encounters the greatest stress.  When I see it fly, that is.  It just seems counter-intuitive to place a hinge right at that extremely high-tension-stress location on the stack.  I thought the folding struts were a CGI flight of fancy and expected a rigid structure of some kind would replace the kewl folding struts, to be honest.

I shouldn't have asked about this prior to the flight.  Now I'll worry about it from liftoff all the way through side core sep... :(
-Doug  (With my shield, not yet upon it)

Online nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #414 on: 12/20/2017 06:00 PM »
Maybe there is a beam that goes through the hinge that takes the load and is retracted after sep to allow the hinge to fold, who knows? I think there will be a lot of people worrying/watching with popcorn all though this launch!

Offline biosehnsucht

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #415 on: 12/20/2017 06:14 PM »
Someone on reddit pointed out what might be stitching errors or some kind of intentional editing.

https://i.imgur.com/PQSPi2z.png

These details along the raceway are lined up in one image, but not in the other. I'm guessing someone was just not paying attention when it came time to stitch, or left it to automated software and it got confused.

Offline sevenperforce

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #416 on: 12/20/2017 06:29 PM »
I have a question about the upper attach structure.  I doubt we will know for certain how it is planned to work until we see the flight, but here goes:

In the detail below, it would appear that the cross-struts that attach tangentially across the center core cannot remain on the center core -- at least where they are right now -- and still allow its grid fins to deploy and have full freedom of movement.  But I would suspect the same thing of the side cores, were these struts to separate in the middle and depart with the side cores.

Do they actually fold up along the side of the interstage on the center core?  Do they stay with the side cores, giving them uneven airflow and thus requiring the additional control authority of the larger titanium grid fins?  Or are they simply jettisoned at some point, a small amount of hardware given up to the rocket equation gods?

Sorry if this has been discussed in detail elsewhere and I have missed it.  It's not humanly possible to read every post in this forum and still maintain heavy life responsibilities... sigh...
They are hinged at the attachment point on the core and fold up. If you look very closely, you can see that the slightly angled rods/arms above the cross-struts (attached to them at the center) have a narrow section and a wide section; those are hydraulic pistons that will retract, pulling the cross-struts up against the core, where they latch into the attachment manifold right above the flag.

I will be quite impressed with a strut system that has a hinge right where it encounters the greatest stress.  When I see it fly, that is.  It just seems counter-intuitive to place a hinge right at that extremely high-tension-stress location on the stack.  I thought the folding struts were a CGI flight of fancy and expected a rigid structure of some kind would replace the kewl folding struts, to be honest.
I'd assume the primary vector for force transfer is at the pair of lower clasps holding the three octawebs together. These struts are likely just to prevent differential yaw/pitch, not to transfer force from the side boosters to the core.

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #417 on: 12/20/2017 06:47 PM »
They remain on the center core and pivot upward. You can see the latches just above the US flag.

Thanks.  I thought those lumps up on the interstage looked like latch points.  And yeah, I recall what the original CGI showed, but the SpaceX CGIs have not always been accurate, especially after several intervening years of design-fiddling.

I will be quite impressed with a strut system that has a hinge right where it encounters the greatest stress.  When I see it fly, that is.  It just seems counter-intuitive to place a hinge right at that extremely high-tension-stress location on the stack.  I thought the folding struts were a CGI flight of fancy and expected a rigid structure of some kind would replace the kewl folding struts, to be honest.

I shouldn't have asked about this prior to the flight.  Now I'll worry about it from liftoff all the way through side core sep... :(

In a good truss system, the individual struts are always hinged, or assumed to be hinged, so do not transfer any torques.
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Offline the_other_Doug

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #418 on: 12/20/2017 06:51 PM »
I'd assume the primary vector for force transfer is at the pair of lower clasps holding the three octawebs together. These struts are likely just to prevent differential yaw/pitch, not to transfer force from the side boosters to the core.

Interesting.  I had always heard that the Shuttle's intertank structure had to be so heavily built was because the upper attach points were where the thrust actually transferred into the stack.  On the Shuttle stack, anyway, most of the thrust transfer happened up top, not down below.  I also recall reading the same comment about the SRB connections on the Titan III and IV family.

Granted, my memory fails me more often than it used to.  But I guess I had been assuming that this was a generic feature of most side-mounted booster systems, and that the upper attach points would be carrying the majority of the load into the stack.  Of course, on a lot of those configs, the lower attach point wasn't, as it is on FH, located roughly where the engine thrust was being transferred to each individual core -- in fact, a lot of those configs had quite different planes along the stack height where thrust transferred into the individual cores.  Perhaps that impacts the stability of using the lower attach points for primary thrust transfer into the stack.

One thing I do know, and that is that a lot of people with engineering degrees have been working on this for years.  If their analyses said the was no problem with the amount of stress being put through a hinge -- no matter how well the main strut is cross-loaded -- then my far less informed worries are probably just that: uninformed worries.

;)
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Offline Archibald

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #419 on: 12/20/2017 06:52 PM »
Saw the pictures on Parabolic arc. And here. what an amazing rocket. Hopefully it won't fire while laying horizontal in the hangar.
Now it only lacks the roadster and fairing. Boom and zoom, onto Mars with Space Oddity.

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