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#100 by Jim on 30 Sep, 2009 00:44
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How the keel pins or any trunnion, would attach to Pirs is TBD at the moment.
That is the whole issue. -
#101 by Danderman on 30 Sep, 2009 01:15
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A. What says the russian docking adapter can take shuttle landing loads? docking loads are much less
This is a very good question. However, the question assumes that the object under consideration is a standard probe and cone system, although it may turn out to be similar but more robust.
To be fair, I should try to answer the question, though. There really are two different kinds of loads to consider during the Shuttle return, continuous and transitory, where the latter are the sharp loads caused by, say, landing on the ground, and the former are the G-loads that are incurred during the actual re-entry itself, plus the 1g vertical load from the 4 ton mass of Pirs.
I am fairly certain that even the standard Russian docking adapter can handle the 1g vertical load, since Progress often maintains ISS on its nose (so to speak) during orbital adjustments - although the Progress engines only generate a fraction of 1g acceleration, ISS has a very large mass; since ISS is not a point mass, and has large dispersions from its c/g (especially with Kibo and Columbus hanging off the sides plus the truss), there are large axial loads on the docking adapter, during these burns, as well. I should mention that the docking hooks and latches are supplemented by clamps during these operations, which help with the loads a bit.
Even more significant are the loads imparted on the Zvezda-Zarya docking adapter when the 2 Zvezda engines provide an orbital correction; although in this case, its a hybrid port handling the loads, the 2 Zvezda engines provide > 600 kg of thrust, which apparently provides noticeable acceleration.
I cannot do the math to calculate the loads with any precision, but its fairly obvious that the loads on the docking adapter are fairly high during these prolonged operations.
As far as the transitory loads, these are precisely what the docking adapter is designed to mitigate. However, once again to be fair, the adapter was not designed to handle axial transitory loads that would be incurred during landing; its good that there would be trunnions to help with those loads.
Note that all of this discussion relates to a hypothetical carrying of Pirs in an upright attitude in the Shuttle cargo bay. There are other attitudes that probably can handle the loads much better.
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#102 by Danderman on 30 Sep, 2009 01:16
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How the keel pins or any trunnion, would attach to Pirs is TBD at the moment.
That is the whole issue.
So, at least we are near the point that if someone figures out how to attach trunnions and a keel pin to Pirs, we are home free. Hopefully, someone here is sharp enough to figure that one out.
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#103 by Danderman on 30 Sep, 2009 01:19
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Here they are attached to the S0 Truss (they needed to be removed once on orbit, as they would have prevented the MT from moving along the S0's rails)
It looks like they have little bolt thingies on the ends that were probably used to connect to the truss elements. If these bolts could be removed on orbit, there is probably a way to use them to connect to Pirs on orbit, as well, as long as are suitable hard points on Pirs.
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#104 by eeergo on 30 Sep, 2009 01:33
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How the keel pins or any trunnion, would attach to Pirs is TBD at the moment.
That is the whole issue.
So, at least we are near the point that if someone figures out how to attach trunnions and a keel pin to Pirs, we are home free. Hopefully, someone here is sharp enough to figure that one out.
This was the purpose of my idea: avoid attaching anything to Pirs transferring the loads to the docking rings at both ends. A pair wider, clamshell-opening rings that would hold Pirs' rings could be included at both ends of the hypothetical cradle. Each one of them would need a keel pin to hold them to the bottom of the payload bay.
A cage-like structure over and below the main body of Pirs would rigidize the system and avoid misalingments/shiftings, and possibly incorporate (or allow for them to be added on-orbit) the trunnions. This could be the concievably foldable structure, or at least disassemblable, so that it wouldn't take up as much volume at launch. The rings could even be launched separately from the main structure.
All this is absolutely armchair speculation, of course, perhaps a structure assembled this way couldn't carry the loads or even be feasibly constructed in space. -
#105 by Danderman on 30 Sep, 2009 03:49
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Remember that any folds must be able to handle loads of 5 tons + at any particular moment. I am not suggesting that this is easy concept to implement, I simply object to arm waving assertions that its "not viable" without looking at the options.
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#106 by Ben the Space Brit on 30 Sep, 2009 10:54
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Just a few thoughts and please remember that I don't have a dog in this fight.
1) The Pirs module was launched by a Soyuz/R7 rocket, so we know that it is engineered to take a Soyuz launch's g-loads along its vertical (SM-to-Soyuz) axis. I will leave it to those more engineering-savvy than me to say upon which axis the maximum g-loads would be during a shuttle's re-entry, descent and landing.
2) If Pirs is being replaced by MLM-1, is is possible to modify the MLM cradle so that it can support Pirs on the way down?
This is an intreguing thought experiment but I have to agree that the benefits of examining Pirs on the ground would be more than outweighed by the cost of developing the tools and proceedures needed to return it. The problem is, unlike those items regularly returend from the ISS, it was never intended for return. Because of this, doing it is that much more difficult and cotostly. Ultimately, if there was no overwhelming pressing reason for doing so, I can't see either NASA or Roscosmos being interested in it. -
#107 by Analyst on 30 Sep, 2009 12:28
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MLM (I assume you mean the Russian module to be launched on STS-132) is not launched in a craddle. It is supported in the payload by its own trunnions.
I still don't see much value in the whole exercise: You can inspect LDEF, EURECA, MISSE or HST elements / experiments if you want to learn about long duration LEO exposure - from months up to more than a decade.
The best solution I see is something like a spacelab pallet on which PIRS would be mounted: Think of HS376 during STS-51A. But I don't see the value.
Analyst -
#108 by Jim on 30 Sep, 2009 13:13
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I am fairly certain that even the standard Russian docking adapter can handle the 1g vertical load, since Progress often maintains ISS on its nose (so to speak) during orbital adjustments - although the Progress engines only generate a fraction of 1g acceleration,
That is not proof and actually means the loads are small. The loads are produced by the thrusters which are low thrust. -
#109 by Jim on 30 Sep, 2009 13:17
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since ISS is not a point mass, and has large dispersions from its c/g (especially with Kibo and Columbus hanging off the sides plus the truss), there are large axial loads on the docking adapter, during these burns, as well. I should mention that the docking hooks and latches are supplemented by clamps during these operations, which help with the loads a bit
No, those loads are not seen at the Progress interface. The Progress only sees the small axial load that the thrusters are causing. It isn't firing side thrusters. Kibo and Columbus interfaces are the ones that see the loads from the offset CG.
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#110 by Jim on 30 Sep, 2009 13:20
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I simply object to arm waving assertions that its "not viable" without looking at the options.
What arm waving? I have not done any of that. You are the one making the gross inaccurate assumptions.
I know it is not feasible. -
#111 by Jim on 30 Sep, 2009 13:22
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MLM (I assume you mean the Russian module to be launched on STS-132) is not launched in a craddle. It is supported in the payload by its own trunnions.
I still don't see much value in the whole exercise: You can inspect LDEF, EURECA, MISSE or HST elements / experiments if you want to learn about long duration LEO exposure - from months up to more than a decade.
The best solution I see is something like a spacelab pallet on which PIRS would be mounted: Think of HS376 during STS-51A. But I don't see the value.
Analyst
Bingo -
#112 by Jim on 30 Sep, 2009 13:29
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Here they are attached to the S0 Truss (they needed to be removed once on orbit, as they would have prevented the MT from moving along the S0's rails)
It looks like they have little bolt thingies on the ends that were probably used to connect to the truss elements. If these bolts could be removed on orbit, there is probably a way to use them to connect to Pirs on orbit, as well, as long as are suitable hard points on Pirs.
What hard points and if there were, what are the chances that they are in the right place?
Drill holes and bolt on or weld on the trunnions and a keel pin. Two things that are not going to happen. Also what fixture is going to provide the precise measurements for aligning the hardware.
It needs a cradle that would "strap" it down or have interfaces with the rings at the ends. -
#113 by Jim on 30 Sep, 2009 13:29
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How the keel pins or any trunnion, would attach to Pirs is TBD at the moment.
That is the whole issue.
So, at least we are near the point that if someone figures out how to attach trunnions and a keel pin to Pirs, we are home free. Hopefully, someone here is sharp enough to figure that one out.
there isn't a way -
#114 by Danderman on 30 Sep, 2009 14:40
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The best solution I see is something like a spacelab pallet on which PIRS would be mounted: Think of HS376 during STS-51A. But I don't see the value.
Analyst
The question is how would Pirs be mounted to the Spacelab Pallet? A Pirs to pallet adapter would have to be created, and someone would raise the following issues:
a) Pirs was not intended to fly on a SpaceLab pallet;
b) The attachments between Pirs and the pallet would have to be installed in space without a system for finely determining the measurements;
in short, all the problems with emplacing Pirs in the shuttle payload bay exist for emplacing Pirs in a SpaceLab pallet.
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#115 by Danderman on 30 Sep, 2009 14:43
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I still don't see much value in the whole exercise: You can inspect LDEF, EURECA, MISSE or HST elements / experiments if you want to learn about long duration LEO exposure - from months up to more than a decade.
This ignores the long debate about prolonging the life of Mir space station; the data from the systems above were not germane to that debate.
I guarantee you at the end of this decade that some will want to end ISS precisely because the condition of the Russian segment will be unknown, and therefore maintaining humans at ISS will be declared risky. We don't have a good baseline for understanding the long term condition of the Russian segment.
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#116 by Jim on 30 Sep, 2009 14:51
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The question is how would Pirs be mounted to the Spacelab Pallet? A Pirs to pallet adapter would have to be created,
Easier than a making a dedicated cradle -
#117 by Jim on 30 Sep, 2009 14:53
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I guarantee you at the end of this decade that some will want to end ISS precisely because the condition of the Russian segment will be unknown, and therefore maintaining humans at ISS will be declared risky. We don't have a good baseline for understanding the long term condition of the Russian segment.
Incorrect. It can be analyzed without inspection. This is done all the time. But there is a baseline, it was called MIR. Also the USOS has elements that are just as old. What is going to be done for it? -
#118 by Danderman on 02 Oct, 2009 13:59
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What hard points and if there were, what are the chances that they are in the right place?
Drill holes and bolt on or weld on the trunnions and a keel pin. Two things that are not going to happen. Also what fixture is going to provide the precise measurements for aligning the hardware.
It needs a cradle that would "strap" it down or have interfaces with the rings at the ends.
In some sense this is a semantic issue, since whatever interface between the Shuttle and Pirs were developed, Jim would claim that this is his "cradle", and therefore he was right, just as with the earlier "why can't they leave an MPLM at ISS" thread, at the end of the day, after months of claiming that "it couldn't be done", when NASA decided it COULD be done, Jim was able to conclude that the modifications to make an MPLM a PLM meant that a MPLM couldn't be left at ISS, so he was right.
In short, if some sort of light and compact cradle, or an alternative set of trunnions and a keel pin were developed, and Pirs were returned, Jim would tell us: "see, you needed a cradle". I am not interested, however, in that semantic argument, what I am interested in are ways to make the return hardware as light as possible and as simple as possible, without sacrificing Shuttle safety requirements.
The major programmatic and technical issues at the moment in returning Pirs are:
1) The Shuttle program has not been extended or stretched yet, so there is no manifest in 2011 or 2012 to return Pirs;
2) There is no base point for the ISS RMS to be located so that it could interface with Pirs;
3) There is no grapple fixture on Pirs.
4) Pirs does not currently have interface hardware for Shuttle return, ie the trunnions and keel pin.
Suggestions on how to address the last three points would be welcome. More posts in the vein of "it can't be done" are not.
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#119 by Danderman on 15 Oct, 2009 03:18
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There have a few videos from Roskosmos on this site lately, related to transport of MRM-2 to and from the vacuum chamber. What is relevant to this thread is that the module, which is virtually identical to Pirs, is transported via 2 large hubs that are somehow attached to the Docking Compartment, ie there are hard points on the exterior of the Docking Compartment which are capable of extremely high loading.
A close look at those hard points indicates that the hubs are attached to the Docking Compartment via a small number of bolts, which is amazing to me - that maybe 8 bolts can handle all of the mass of the Docking Compartment. Of course, getting back to this thread, if a way to connect those hard points to trunnions could be developed, then transport of Pirs in the Shuttle payload bay may be possible.
