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Old 08-30-2018, 09:10 PM   #1981
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 For the last couple days I have been trying to figure out why the GOX vents through MPS intermediate seal turbopump drain lines doesn't want to line up. I've checked everything. Everything seems to check out. Is there some logic I'm missing in the set up? The actual coordinates is with the nozzles in the installed NULL positions which I got directly from AC3D.

https://www.dropbox.com/s/24l5l3wrzh...vents.jpg?dl=0
I've seen that before, and figured why that wasn't working... but I'm not remembering all the details. I think it has to do with the initial position of the engines.... for some reason I didn't, or more likely couldn't fix it.
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Old 08-30-2018, 09:15 PM   #1982
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 I've seen that before, and figured why that wasn't working... but I'm not remembering all the details. I think it has to do with the initial position of the engines.... for some reason I didn't, or more likely couldn't fix it.
So should I just leave things as-is for the moment?
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Old 08-30-2018, 10:21 PM   #1983
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 So should I just leave things as-is for the moment?
Yes, when I'm more "free" from TAEM guidance I'll take a look again.
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Old 09-06-2018, 04:17 PM   #1984
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I'm finishing up the orbiter and I got a problem. I need to tilt the orbiter when it is attached to the ET to get the proper alignment between the forward and aft attachment points. Where in the code can I change the direction and rotation of the orbiter attachment point to the ET? I got the vectors ready but I need to know where they go.
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Old 09-06-2018, 06:24 PM   #1985
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 I'm finishing up the orbiter and I got a problem. I need to tilt the orbiter when it is attached to the ET to get the proper alignment between the forward and aft attachment points. Where in the code can I change the direction and rotation of the orbiter attachment point to the ET? I got the vectors ready but I need to know where they go.
I'm not sure that will be possible to do, at least not in a couple of minutes (or more likely hours), as the engines are coded to point to the c.g., which is calculated assuming the ET and OV are aligned, yada, yada, yada...
I'm currently putting the final touches on TAEM and am already thinking Entry guidance, so only after that will I have my brain "free" for other big things.

For now I suggest splitting the difference between the fwd and aft attach points, leaving the orientation as is, and updating ticket 186 to reflect this remaining work.
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Old 09-06-2018, 06:34 PM   #1986
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 I'm not sure that will be possible to do, at least not in a couple of minutes (or more likely hours), as the engines are coded to point to the c.g., which is calculated assuming the ET and OV are aligned, yada, yada, yada...
I'm currently putting the final touches on TAEM and am already thinking Entry guidance, so only after that will I have my brain "free" for other big things.

For now I suggest splitting the difference between the fwd and aft attach points, leaving the orientation as is, and updating ticket 186 to reflect this remaining work.
One thing that has to be done along side ticket 186 is the animation of the umbilical disconnect plates so that they mate properly with the ones on the ET.
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Old 09-06-2018, 06:55 PM   #1987
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Also, if the orbiter is suddenly angled relative to ET and SRBs, we might need to check if the SRB thrust vectors and hold down posts are still implemented properly.
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Old 09-06-2018, 07:10 PM   #1988
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 Also, if the orbiter is suddenly angled relative to ET and SRBs, we might need to check if the SRB thrust vectors and hold down posts are still implemented properly.
AFAIK, The ET/SRBs have a neutral pure vertical angle so there shouldn't be any changes there. The reason for the angled orbiter is that the forward attachment point (the bipod struts/yoke) are taller than the aft ball/socket joints. The bipod has height of 56.341" (1.431 m) while the aft ball/socket joints have a height of 41.259" (1.048 m). As you can see, the aft sits lower than the forward, creating a disconnect between the two if the angle was flat and level.


For reference, the separation planes for the bipod and ball/socket joints are as follows:
Xo283.841 (bipod)
Xo267.556 (aft ball/socket).
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Old 09-06-2018, 07:16 PM   #1989
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 AFAIK, The ET/SRBs have a neutral pure vertical angle so there shouldn't be any changes there. The reason for the angled orbiter is that the forward attachment point (the bipod struts/yoke) are taller than the aft ball/socket joints. The bipod has height of 56.341" (1.431 m) while the aft ball/socket joints have a height of 41.259" (1.048 m). As you can see, the aft sits lower than the forward, creating a disconnect between the two if the angle was flat and level.


For reference, the separation planes for the bipod and ball/socket joints are as follows:
Xo283.841 (bipod)
Xo267.556 (aft ball/socket).
... and the bipods couldn't be made to fit the OV, because...??? The more I think about a "titled OV", the more it doesn't make sense...
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Old 09-06-2018, 07:35 PM   #1990
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 ... and the bipods couldn't be made to fit the OV, because...??? The more I think about a "titled OV", the more it doesn't make sense...
It is angled. Not by much, just 0.1. They do angle the orbiter when it's mated to everything else, including the OTS and the SCA. It's the same for both, 2s. For the ALTs, the angle was raised to 5s by the use of a taller bipod assembly on the SCA.

---------- Post added at 09:35 PM ---------- Previous post was at 09:24 PM ----------

You might be interested in this document: Space Shuttle Separation Mechanisms
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Old 09-06-2018, 10:33 PM   #1991
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 It is angled. Not by much, just 0.1. They do angle the orbiter when it's mated to everything else, including the OTS and the SCA. It's the same for both, 2s. For the ALTs, the angle was raised to 5s by the use of a taller bipod assembly on the SCA.

---------- Post added at 09:35 PM ---------- Previous post was at 09:24 PM ----------

You might be interested in this document: Space Shuttle Separation Mechanisms
Yes, it is visibly nose-up in the SCA, but the requirements are totally different: the OV sits passively in the SCA, versus having to point engines and manage IMU and RGA data during launch. I'm not saying it is impossible, just that it adds extra complexity, so there must be a very good reason to do so. Where did those 0.1 come from?

BTW: I read the document "in the diagonal" and it doesn't seem to add anything to this discussion.
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Old 09-07-2018, 09:08 AM   #1992
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Well, remember we are using the orbiter body coordinate system and all others (ET, SRB) are relative to the orbiter, even on the pad. Its no really big problem for the stack and can even be ignored for SCA and others.

But any such alignment should be handled with care, because a lot depends on it.
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Old 09-07-2018, 10:58 AM   #1993
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This is with the orbiter perfectly level on the ET with the attachment point being right for the bipod: https://www.dropbox.com/s/yxoc5ghrgs...OV_ET.jpg?dl=0


As you can see we got interference with the aft diagonal thrust struts when in reality the orbiter sits a bit above them and the cross-beam. This photos shows it quite well: https://www.flickr.com/photos/apacheman/5801795963/ as does this schematic of the aft ET hardware: https://www.dropbox.com/s/usklpunf1n...ments.jpg?dl=0

And this is with a 0.2 angle: https://www.dropbox.com/s/zlbcrhfp1f...angle.jpg?dl=0

---------- Post added at 12:58 PM ---------- Previous post was at 12:33 PM ----------

The 0.2 angle also negates the angle of the umbilical disconnect plates on the orbiter which are also angled due to the bottom shape of the orbiter aft engine compartment.

Last edited by DaveS; 09-07-2018 at 10:39 AM.
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Old 09-07-2018, 02:52 PM   #1994
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 This is with the orbiter perfectly level on the ET with the attachment point being right for the bipod: https://www.dropbox.com/s/yxoc5ghrgs...OV_ET.jpg?dl=0


As you can see we got interference with the aft diagonal thrust struts when in reality the orbiter sits a bit above them and the cross-beam. This photos shows it quite well: https://www.flickr.com/photos/apacheman/5801795963/ as does this schematic of the aft ET hardware: https://www.dropbox.com/s/usklpunf1n...ments.jpg?dl=0

And this is with a 0.2 angle: https://www.dropbox.com/s/zlbcrhfp1f...angle.jpg?dl=0

---------- Post added at 12:58 PM ---------- Previous post was at 12:33 PM ----------

The 0.2 angle also negates the angle of the umbilical disconnect plates on the orbiter which are also angled due to the bottom shape of the orbiter aft engine compartment.
In other words, there is not "official" or direct data that says the OV is angled*, only measurements that work better with an angle... well, in this particular case that is not going to be enough to change code, as the implications of that angle not being 0 are just too big.
IMO, the likelihood of one of those measurements having an error (in value, conversion or just tolerance stack-up) is higher than the OV being at an angle, when we consider the GNC issues that would bring (that again, are not insurmountable).

*) in fact, doesn't the SODB (or the large diagrams books) have some diagrams with the axis of the 4 stack components, and their axis matching each other?
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Old 09-07-2018, 03:03 PM   #1995
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 In other words, there is not "official" or direct data that says the OV is angled*, only measurements that work better with an angle... well, in this particular case that is not going to be enough to change code, as the implications of that angle not being 0 are just too big.
IMO, the likelihood of one of those measurements having an error (in value, conversion or just tolerance stack-up) is higher than the OV being at an angle, when we consider the GNC issues that would bring (that again, are not insurmountable).

*) in fact, doesn't the SODB (or the large diagrams books) have some diagrams with the axis of the 4 stack components, and their axis matching each other?
Well, the angle is very minute and documents with graphics have a very hard time showing very minute details such as sub-degree angles. I just drew a line 0.2 line myself in Paint.NET and it is not even detectable. I can ask someone who should definitely know, a retired NASA-KSC Shuttle Mechanical Systems (group callsign MEQ) engineer who worked alot of orbiter/ET mates (and few demates) right up to the very end. He should know if the the orbiter had an angle when mated.
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