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#220 by roma847 on 22 May, 2013 09:44
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But there is also another problem.
When fastening the SRBs on their supports and hold-down posts, I must note that the stack cannot stand without a prop under the orbiter and therefore needs a support. When the stack is built it'll have some weight and the orbiter will make it heavier on one side.
The eight pins (0.5 mm) in the hold-down posts serve only the fixation of the stack on the SRB supports. I'll chose the slightly larger bores (0.8 mm) in the SRB aft skirt hold-down posts only in order to be able to thread the stack better over these eight pins.
A solution for the support of the stack, I've been thinking a long and I have some ideas for scratch-building it.
First of all I imagine a horizontal support bar, which runs through both TSMs and the orbiter, in the height of the umbilicals. The bar could be one-piece and continuously, or I could imagine two shorter rods, which are inserted from both outer faces through the TSMs into the orbiter. These bars are likely to be hardly to see in the TSM walls.
This solution could also work, if the TSMs are not glued on the MLP deck, but if the TSMs with this support bars through the umbilicals are only placed near to the orbiter and support him so. Then, you have to find a solution to the TSM SSWS pipes.
Source: NASA
A second solution would also be possible:
In both SRBs bottoms threaded rods are screwed from below, ranging through the SRB holes a few millimeters over the MLP ground. On these threaded rods a hold-down clamp made of a metal strip (85x5x2 mm) is screwed with nuts. Then you might not need a support rod through the TSMs if the orbiter would be fixed by the double umbilical connections.
Currently I tend to the first solution with one or two rods in the TSMs.
Or are there other proposals from you too?
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#221 by Lar on 22 May, 2013 13:44
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What about using the closeout room to hold the orbiter from tipping backwards? That's assuming you are building the service structures, though. It would apply a fair bit of torque to the tower.
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#222 by OV135 on 22 May, 2013 14:21
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You could extend the TSM attach points to where it touches the orbiter go into an L shape with the bottom of the L go under and hold up the orbiter. This prevents it from tipping forward.
As to tipping back. I was thinking of drilling holes into where the SRB hold down points are. Once that's done you add pints to the hold down posts themselves. You line up the pieces and the posts anchor the stack to the MLP. I mean this fits with the RL photos of the bolts holding down the boosters to the pad. As in this diagram.
http://www.raumfahrer.net/forum/yabbfiles/Attachments/up029122.jpg -
#223 by roma847 on 22 May, 2013 23:23
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What about using the closeout room to hold the orbiter from tipping backwards? That's assuming you are building the service structures, though. It would apply a fair bit of torque to the tower.
That's right, this would be also a possibility, a solid connection between the White room at the end of the Orbiter Access Arm (OAA) of the Launch tower (FSS) and the orbiter.
Source: NASA
But this would mean that the stack should always be connected with the OAA and could not stand independent on the MLP without any kind of support, what I but also does not want to exclude.
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#224 by roma847 on 22 May, 2013 23:36
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You could extend the TSM attach points to where it touches the orbiter ...
And this is the way I want to go, because I think that the lateral support rods from outside the TSMs through the Umbilical interface into the orbiter seems to be the best solution for stabilisation of the stack.
Source: NASA
I think, because there already some pipes and cables run through this interface, the support rods will hardly attract attention.
Source: NASA
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#225 by Lar on 23 May, 2013 00:23
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But this would mean that the stack should always be connected with the OAA and could not stand independent on the MLP without any kind of support, what I but also does not want to exclude.
Yep. Your idea of running pins through the TSMs is much better. Especially if you can make the pins removable so the stack can be removed if you wanted to
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#226 by roma847 on 23 May, 2013 07:36
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Yep, that's my intention and all what I want.
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#227 by mike robel on 23 May, 2013 12:23
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What about adding weight to the bottom of the SRBs and/or ET to shift the center of gravity of the stack so it stays verticle by itself?
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#228 by roma847 on 23 May, 2013 12:56
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These are all possible approaches, they must be only be realizable on the model. You will understand that soon if you can see what small dimensions it is.
In particular the unfavourable ratio of the nearly point-shaped SRB stands on the Hold-down posts to the considerable height of the stack is the absolute k.o. criterion, and therefore the danger that could topple the stack is too large.
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#229 by RichO on 25 May, 2013 13:02
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MANFRED,
I like the rods through the TSM into the tail also. Most people would never see it, good call!
RichO -
#230 by roma847 on 27 May, 2013 14:42
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Hi Richo,
I fully agree with you, this will be the most viable solution.
And here is the next update, and so back to various detail work on the SRB supports and their Hold-down posts.
Because the Aft skirt hold-down posts of the SRBs with 2 mm are very narrow, I have carefully pre-drilled the holes for the bolts (0.5 mm) for the fixing of the stack with the gimlet first with 0.5 mm,
and drilled then for easier threading of the stack to 0.8 mm diameter.
And the Hold-down posts are constructed from these parts.
The cone tips get cores of a 3.3 mm rod with a 0.5 mm hole for the reception of the bolt pins (0.5 mm). The cone tips sit on a base plate (1.5 mm) and receive above as the Aft skirt shoe a small plate from sheet 4x4x1 mm.
This is now such a pre-assembled body for the Hold-down post (left) and next to it an attempt for the side locking pin of the Shoe retainer mechanism, which however still not convinced me.
Since this solution with the coated brass wire (blue) seems manufactured bit too time-consuming from processing, I further considered and once cut the rods.
Therefore here now another attempt made of plastic with a square profile (1 mm), with a glued rod (0,8 mm) as bolt.
This allows then but easier to produce and I like even better, as you can see on this picture.
And so I will also build now the remaining seven Hold-down posts. And most recently the small Blast shields come then to the top of the rear Hold down posts.
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#231 by DaveS on 27 May, 2013 16:19
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To increase the stability you could add the shear weight of the SRB propellant. This will move the c.g of the stack towards the SRBs and the holddown posts just like on the real vehicle. Not even fully loaded the orbiter+ET approaches the total weight of the two SRBs.
Currently you have the majority of the weight in the Orbiter, when this should not the be the case. This leads to the stack tilting backwards. -
#232 by roma847 on 28 May, 2013 13:40
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Thanks Dave for your comments. That is quite right, the change in the weighting of the stack should improve its stability. This prevents but not the tilting danger of the stack, especially when vibrations or shocks and therefore the crash risk of the stack is then too large to me without any front support of the orbiter.
I think in particular the unfavourable ratio of the nearly point-shaped SRB stands to the considerable height of the stack is essential and the absolute k.o. criterion.
BTW Dave, still another question. Do you know when (up from which STS-?) the small Blast shields at the top of the Holddown posts were red painted instead of gray? I suppose that they were painted grey during the early missions, perhaps STS-6 too?
Source: NASA
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#233 by RichO on 30 May, 2013 20:40
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MANFRED
I am also keeping an eye out for your STS-6 blast shield color. Someone will come across a photo with the correct color, then we will all know.
Keep up the good work on all the small details, really great!
RichO 114 -
#234 by roma847 on 02 Jun, 2013 21:36
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Thanks Richo for the nice words, this question is perhaps too specifically, maybe I find even a response.
Now it went a little further with the Hold-down posts again, and the little things keep pretty one, if you can not hold on building.
These are the necessary items for the remaining seven Hold-down posts, until on the lateral retaining bolts of the Shoe retainer mechanism.
After the cone tips were shortened to the required height, the rods (3.3 mm) were cut and received a through hole (0.5 mm). Then they were pasted in the cone tips and then glued onto the bases.
On the top the small plates (Aft skirt shoe) were then glued, and yet the 0.5 mm bolts were glued into the holes.
So, that's about it first time today.
Now missing only the side locking bolts, which should follow tomorrow.
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#235 by RichO on 04 Jun, 2013 00:15
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MANFRED,
Thanks for the encoragement, so many tiny parts to deal with. I just have to keep going to get things ready for the material I ordered.
Your hold down posts are looking great, I really want to see how these turn out. Keep up the great work!
Richo 114 -
#236 by roma847 on 04 Jun, 2013 21:15
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Thanks Richo for the nice words, I'll try to give my best.
Since the parts for the side locking bolts are only such short stubs of about 2,5 - 3,5 mm, it is better, if only together sticks the profiles,
and cuts only after drying on length, so this is really easier.
Now the stubs only on both sides must be glued,
and then they are available for painting.
But before there is another alignment test on the support, 
and so the Boosters are standing on it.
And if the Hold-downs are first then painted and will stick firmly to the supports, then I can breathe again.
As far as for today.
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#237 by RichO on 05 Jun, 2013 17:41
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MANFRED,
The hold down posts turned out so cool, great idea with the pen tips. Now off to the paint department with them. Thanks for the photo, I am constantly amazed about how frikin' big and massive everything about the space program is, just amazing.
RichO -
#238 by roma847 on 06 Jun, 2013 12:58
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Thanks Richo for the encouraging words.
Next, the hold downs are painted, and I would be glad if they would stick to the correct position on the SRB supports.
And now I will turn again to the TSMs, but this time in 1:144, otherwise the same procedure like ever in 1:160.
The TSM parts look on the Paper kit in such a way:
In the building guidance all steps are illustrated in detail.
Although both TSM's from the outside form look almost alike, they differ nevertheless in some details, which will still have to be seen. I began first with the right TSM, by which the pipes for the liquid oxygen (LOX) run.
As next step I have to make reinforcement Sub-Supports for the TSM cover, for which I will use Balsa, to get the required thickness.
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#239 by RichO on 06 Jun, 2013 18:01
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GO MANFRED, GO!!
And watch out for exploding ticket machines.
RichO
