Author Topic: Racks and Rack Positions  (Read 25946 times)

Offline Herb Schaltegger

Re: Racks and Rack Positions
« Reply #60 on: 02/18/2009 02:25 AM »
Look, you know I'm not trying to promote LEGO space ships. It just seems to me that modular space stations should be a lot easier to design than modular launchers. From what Herb said it sounds as if doing this within current limitations is so difficult it may even be impossible.

There are things about design requirements for pressurized element module interfaces that are not intuitive at all.

For instance. verification.  When two modules berth, before you open the hatches between the two, you have to verify that the air inside the vestibule is safe to breathe.  That means that either you show via analytical means that there is no way any kind of gaseous toxin is present in concentrations greater than SMAC (Spacecraft Maximum Allowable Concentration); OR that you have means to sample the gases inside that vestibule for such toxins to determine presence and/or concentrations.  Well, you think, what could possibly exist in between two modules just recently berthed to one another in vacuum?  Well, for the space station, you have the potential at least for two big ones: hydrazine from hypergolic propulsion systems and ammonia from the station external TCS.  No vacuum is perfect and the "vacuum" around the station is far from perfect. Since you therefore cannot analytically "prove" that the vestibule will be toxin-free, you have to include provisions for actual testing of the atmosphere in the enclosed space.

In addition, even once you berth modules and open one hatch to the vestibule, you have to be able to verify that the conditions inside the newly-added module are habitable.  Again, you have to be able to pull samples and test them to ensure that conditions are safe before opening the second hatch. 

Now, complicating matters further . . . contingency planning!  Imagine a week, a month, a year, five years after the module is berthed, there is a fire inside one of the modules.  Make it a node, to complicate matters.  Worse, there are crew inside Columbus that can't get through the Node (it's a big, science fiction movie-sized fire)  :-)  So now we've got two closed-off modules, one of which is PROBABLY okay (Columbus) and the other of which is likely filled with combustion by-products, high levels of CO, CO2, and who knows what else.  So you remotely vent the atmosphere of the node, then repressurize.  But you really don't want to expose crew members trapped in Columbus to whatever might still be in the Node until you're sure it's safe, or at least know what they could be exposed to.

So all this means that ideally you want to be able to REMOTELY verify the atmosphere of any given module, not just from right next door.  This requires a system of sampling tubes that run throughout the station to locations within each module, and which run back to the TCM (Trace Contaminant Monitor, for over a hundred different potential contaminants) and the MCA (Major Constituent Analyzer, for O2, N2, CO2, H2O and one or two others, IIRC).  There are (or were anyway) requirements to be able to pull a sample from any location within so many minutes, including "flush" time to ensure that the air sampled is actually representative of what's currently in the module).  This required a very elaborate system of sampling lines for the modules and solenoid isolation valves for each line at a couple of places within each module.  And since the sampling route can vary from module to module depending on which module you want to sample and the station configuration during the assembly process, you need more than one line to do this.

Now this is just for atmosphere sampling and verification.

Another non-intuitive design requirement is human-factors.  These interfaces were designed to comply with a big book of requirements called NASA-STD-3000.  This NASA Standard specified certain minimum spacing between connectors so that astronauts in pressure suits would be able to manipulate connectors.  The connectors were designed to require certain minimum and maximum forces to mate and demate. 

A third non-intuitive design requirement is (or was, at least) maintainability.  The original design lifetime was 30 years (!!!!).  That a long time.  Connector springs wear out.  Elastomeric seal materials degrade and begin to leak.  Flexible out covering materials for fluid and data jumpers begins to age, off-gas (usually toxic chemicals, BTW) and become brittle.  So not just the fluid jumpers but the actual connectors themselves had to be designed to be removed and replaced on the vestibule interface bulkheads (I don't know if that requirement still exists with the shortened life requirements of ISS).

Anyway, these requirements taken all together ended up meaning that there just couldn't be a one-size-fits-all interface for station pressurized elements.
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Offline bobthemonkey

Re: Racks and Rack Positions
« Reply #61 on: 02/18/2009 02:45 AM »
The Nadir CBM is being converted into a PVGF so that SPDM can be based there.

Nadir? Isn't this the place for the Cupola?

Analyst

Sorry, I was waaaay too tired last night.  Zenith.

So this means the Zarya PDGF is back off the table again?

Online Ronsmytheiii

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Re: Racks and Rack Positions
« Reply #62 on: 02/18/2009 04:08 AM »
The Nadir CBM is being converted into a PVGF so that SPDM can be based there.

Nadir? Isn't this the place for the Cupola?

Analyst

Sorry, I was waaaay too tired last night.  Zenith.

So this means the Zarya PDGF is back off the table again?

Nothing to do with that, PVGF is Power Video Grapple Fixture
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Offline bobthemonkey

Re: Racks and Rack Positions
« Reply #63 on: 02/18/2009 10:48 AM »
I ask because of a reference on L2 8th Floor ISS News.
« Last Edit: 02/18/2009 07:19 PM by Chris Bergin »

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Re: Racks and Rack Positions
« Reply #64 on: 02/18/2009 04:37 PM »
There are things about design requirements for pressurized element module interfaces that are not intuitive at all.

Thanks for that detailed information (you too Jim), you have given me a taste of how complicated this is.

Quote
Anyway, these requirements taken all together ended up meaning that there just couldn't be a one-size-fits-all interface for station pressurized elements.

Would you agree with Jim that more or bigger hatches would be too heavy to be a solution? I wonder by how much they would be too massive. Is there some convenient scaling law to predict that? And how much bigger would they have to be before volume constraints were no longer a problem?

I guess I'm trying to find out if the hypothetical ISS2 modules discussed in the ISS extensions thread could have universal plumbing or at least enough flexibility so the station would not have an irreplaceable core module that limits its lifetime.
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Offline Herb Schaltegger

Re: Racks and Rack Positions
« Reply #65 on: 02/18/2009 04:52 PM »
It's all in the requirements.  If you were satisfied with zero fault-tolerant atmospheric sampling, for instance, you could have a single line running throughout the station from one module to the next, etc., with lines tee-ing off it for sampling in discrete locations. That would simplify the module interfaces quite a bit.  Similarly, power connections, data connections, etc., could all be single connections between modules.  Of course, failure of one connector, one valve, a bent or broken wire inside a data connector, renders that system useless.

Alternately, remove vacuum access requirements (and the requirement to be able to make connections by a suited crewmember wearing pressure gloves) and you can pack things in much more tightly.  Shorten lifespan requirements and you can make connectors (and seals, springs, etc.) smaller and lighter. 

Hatch size was determined based on rack size combined with pressure-holding requirements.  Force = Pressure * Area.  There's a LOT of force on the seals and mechanisms of a pressure hatch that size as it is. Oh, and those seals have to be redundant AND verifiably so.  You'd like to know, wouldn't you, if two of the three seals have eroded before the third one goes and depressurizes your module, right?  That means leak-check ports between seals.  Now, if you carry this requirement down to the seals on the vestibule feed-throughs used for the power/data/fluid couplings, those couplings get that much bigger, heavier, and more expensive.

It's all a trade-off of requirements versus mass, volume, power/data, and ultimately cost.
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Offline robertross

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Re: Racks and Rack Positions
« Reply #66 on: 02/18/2009 11:20 PM »
Damn, Herb...I deal with this type of stuff at work, but never put it into context for ISS. Thanks for that great explanation. All the sampling lines, probably stainless, all independant running through the modules. Obviously the serviceability of solenoid valves to isolate & purge a tee-ring design is self defeating in the end...

Don't want to stray the thread too OT though.

Are most of the racks local controlled (IE: software, settings) with remote ops, or is it mostly dependant on the racks themselves depending on the level of ground/crew involvement required?
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Offline Herb Schaltegger

Re: Racks and Rack Positions
« Reply #67 on: 02/19/2009 07:02 PM »
Damn, Herb...I deal with this type of stuff at work, but never put it into context for ISS. Thanks for that great explanation. All the sampling lines, probably stainless, all independant running through the modules. Obviously the serviceability of solenoid valves to isolate & purge a tee-ring design is self defeating in the end...

Don't want to stray the thread too OT though.

Are most of the racks local controlled (IE: software, settings) with remote ops, or is it mostly dependant on the racks themselves depending on the level of ground/crew involvement required?

316L stainless.  ;) 

(My name's on the base, and Rev. A through around B/C range for most of the design drawings for that stuff for the ARS, buried deep, deep inside some MSFC and Boeing data archives).
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Offline robertross

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Re: Racks and Rack Positions
« Reply #68 on: 02/20/2009 12:42 AM »

316L stainless.  ;) 

(My name's on the base, and Rev. A through around B/C range for most of the design drawings for that stuff for the ARS, buried deep, deep inside some MSFC and Boeing data archives).

I can even get the sense of pride from your statement, and rightly so. Quite an engineering masterpiece. Nice to talk with one of the creators. :)

Good old 316L. I wonder if they use Swagelok for those tubes & fittings, or possibly Parker instrumentation. I used to be a hydraulics plumber (among other jobs), but now have a desk job. Now I get to complain when someone doesn't follow one of my drawings correctly, or they don't know how to bend tube (it's an art).
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Offline Herb Schaltegger

Re: Racks and Rack Positions
« Reply #69 on: 02/20/2009 02:44 AM »

316L stainless.  ;) 

(My name's on the base, and Rev. A through around B/C range for most of the design drawings for that stuff for the ARS, buried deep, deep inside some MSFC and Boeing data archives).

I can even get the sense of pride from your statement, and rightly so. Quite an engineering masterpiece. Nice to talk with one of the creators. :)

Good old 316L. I wonder if they use Swagelok for those tubes & fittings, or possibly Parker instrumentation. I used to be a hydraulics plumber (among other jobs), but now have a desk job. Now I get to complain when someone doesn't follow one of my drawings correctly, or they don't know how to bend tube (it's an art).

Man that brings back some memories . . . the Parker (Parker Hannifin in those days) rep was a real social butterfly - he was always dropping off catalogs and technical info and trying to schmooze us. I don't recall who we ended up sourcing on some of that stuff.  We sourced a bunch of the solenoid valves from Carleton up in Orchard Park, NY if I remember correctly.

Anyway, SSF was a fun project.  I wish it had been more politcally popular - I might still be an engineer instead of taking a 180 on my career. 
« Last Edit: 02/20/2009 02:44 AM by Herb Schaltegger »
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Offline dwb0407

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Re: Racks and Rack Positions
« Reply #70 on: 03/15/2009 11:38 AM »
To continue the CBM discussion...

In my mind I have the logical requirement that we will eventually need PMA2 and PMA3 (with some adapter perhaps) to do US crew change out (whether it's Orion or COTS-D or whatever). So that's two "un-obstructed ports" needed. I'll assign Node 2 Forward and Nadir for now.

We could get away with having just one "Cargo" berthing port, ie Node 2 Zenith, but that seems short sighted to me. With the current expectation for HTV, Dragon and Cygnus having two would be nice. But more from a contingency stand point having a backup is a good idea.

If Node 3's currently unused ports are not made useable from the start as has been suggested, we are out of ports.

I understand that when attached to Node 1 Port all of the remaining CBMs are obstructed, however a future relocation (post shuttle), to Node 2 nadir (with PMA 3 going where it was originally planned to go new node 3 nadir) would open the ports up. (I'd put Cupola on the new node 3 aft at this point, see the whole station and earth).

I"m not suggesting that we plan ahead for future modules, simply outfit Node 3 cbm's for what is necessary for HTV, Dragon, Cygnus berthing. If the one remaining node 2 CBM becomes damaged or worn out, supply gets really tricky if node 3 is hatchless.

It has just occurred to me however that Node 2 might not be piped correctly for a Nadir Module, perhaps it was piped for a Zenith instead. We've had ELM-PS up there (fully understanding that ELM-PS is not a full module of any sort)

Basically it comes down to needing 2 pma's and 2 available berthings in final config. Not sure how to do that without usable Node 3 CBMs

ARED causes other issues to my hypothetical arrangement. It's quite obtrusive. And would not be friendly to unloading a docked cargo craft. Is there any reason that it could not be returned it's current node 1 position?

And to whom ever said that they don't expect to see MRM-1, aren't we required to launch that for the Russians, when are they expected to deliver it to the cape? Does anyone have a real sense of it's current status.

Don

Offline Analyst

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Re: Racks and Rack Positions
« Reply #71 on: 03/15/2009 12:53 PM »
1) It has just occurred to me however that Node 2 might not be piped correctly for a Nadir Module, perhaps it was piped for a Zenith instead. We've had ELM-PS up there (fully understanding that ELM-PS is not a full module of any sort)

2) Basically it comes down to needing 2 pma's and 2 available berthings in final config. Not sure how to do that without usable Node 3 CBMs

3) ARED causes other issues to my hypothetical arrangement. It's quite obtrusive. And would not be friendly to unloading a docked cargo craft. Is there any reason that it could not be returned it's current node 1 position?

4) And to whom ever said that they don't expect to see MRM-1, aren't we required to launch that for the Russians, when are they expected to deliver it to the cape? Does anyone have a real sense of it's current status.

Don

1) Last MPLM (STS-126) has been at Node 2 nadir.
2) You missed one place: Node 1 nadir. So you have two PMAs at Node 2 (forward and nadir), and one CBM (zenith). Plus one CBM at Node 1 nadir (currently PMA 3 is there).
3) My understanding is ARED at Node 1 "blocks" two CBMs (nadir and port). With Node 3 at port it has to move into Node 3, there is takes basically two CBMs too.
4) It is baselined for STS-132.

Analyst
3)

Offline MBK004

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Re: Racks and Rack Positions
« Reply #72 on: 03/15/2009 02:41 PM »
It has just occurred to me however that Node 2 might not be piped correctly for a Nadir Module, perhaps it was piped for a Zenith instead. We've had ELM-PS up there (fully understanding that ELM-PS is not a full module of any sort)

The CAM was to be at Node 2 Zenith.

Offline ShuttleDiscovery

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Re: Racks and Rack Positions
« Reply #73 on: 03/16/2009 07:54 AM »
To continue the CBM discussion...

In my mind I have the logical requirement that we will eventually need PMA2 and PMA3 (with some adapter perhaps) to do US crew change out (whether it's Orion or COTS-D or whatever). So that's two "un-obstructed ports" needed. I'll assign Node 2 Forward and Nadir for now.

We could get away with having just one "Cargo" berthing port, ie Node 2 Zenith, but that seems short sighted to me. With the current expectation for HTV, Dragon and Cygnus having two would be nice. But more from a contingency stand point having a backup is a good idea.

If Node 3's currently unused ports are not made useable from the start as has been suggested, we are out of ports.

I understand that when attached to Node 1 Port all of the remaining CBMs are obstructed, however a future relocation (post shuttle), to Node 2 nadir (with PMA 3 going where it was originally planned to go new node 3 nadir) would open the ports up. (I'd put Cupola on the new node 3 aft at this point, see the whole station and earth).

I"m not suggesting that we plan ahead for future modules, simply outfit Node 3 cbm's for what is necessary for HTV, Dragon, Cygnus berthing. If the one remaining node 2 CBM becomes damaged or worn out, supply gets really tricky if node 3 is hatchless.

It has just occurred to me however that Node 2 might not be piped correctly for a Nadir Module, perhaps it was piped for a Zenith instead. We've had ELM-PS up there (fully understanding that ELM-PS is not a full module of any sort)

Basically it comes down to needing 2 pma's and 2 available berthings in final config. Not sure how to do that without usable Node 3 CBMs

ARED causes other issues to my hypothetical arrangement. It's quite obtrusive. And would not be friendly to unloading a docked cargo craft. Is there any reason that it could not be returned it's current node 1 position?

And to whom ever said that they don't expect to see MRM-1, aren't we required to launch that for the Russians, when are they expected to deliver it to the cape? Does anyone have a real sense of it's current status.

Don

I agree with you. If Node 3 can't be attached to Node 1 nadir anymore because of MRM1 clearance issues, then Node 2 nadir seems like the best place to put it. Furthermore, having Cupla facing aft is much better as you can see the whole ISS, and the earth. However it's unrealistic to have Node 3 on Node 2 nadir when the shuttles are still visiting, and it's also unrealistic to relocate it from Node 1 port to Node 2, so I think on STS-130 they shoukd berth Node 3 to Node 2 zenith, then after STS-133/4, relocate it to Node 2 nadir. This way there are 4 available ports: Node 3 forward (underneath PMA2, may cause clearance issues with Orion), Node 3 port (underneath Kibo), Node 3 starboard (underneath Columbus) and Node 3 nadir (ideal for PMA3 if unusable attached to Node 1 nadir).

This allows for much more expansion such as MPLM Donatello and for COTS vehicles like you mentioned. No matter what NASA are planning, I'm sure they'd want 4 usable ports rather than 0.

Offline Analyst

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Re: Racks and Rack Positions
« Reply #74 on: 03/16/2009 11:47 AM »
Did you even read my post? There are currently 5 free ports on orbit:

- Node 1 nadir (PMA-3)
- Node 1 port (CBM)
- Node 2 zenith (CBM)
- Node 2 nadir (CBM)
- Node 2 front (PMA-2)

Whereever you put Node-3 - and independent of relocating PMAs or not - you will always have 2 PMAs and 2 CBMs left. There is no shortage of docking ports.

Node-3 at Node-2 is not needed. And it is not possible: S0 carries (since launched in 2002) Node-3 umbilicals (power, ammonia cooling) to connect it directly to S0. This won't work being at Node-2.

Analyst

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Re: Racks and Rack Positions
« Reply #75 on: 03/16/2009 11:55 AM »
Did you even read my post? There are currently 5 free ports on orbit:

- Node 1 nadir (PMA-3)
- Node 1 port (CBM)
- Node 2 zenith (CBM)
- Node 2 nadir (CBM)
- Node 2 front (PMA-2)

Whereever you put Node-3 - and independent of relocating PMAs or not - you will always have 2 PMAs and 2 CBMs left. There is no shortage of docking ports.

Node-3 at Node-2 is not needed. And it is not possible: S0 carries (since launched in 2002) Node-3 umbilicals (power, ammonia cooling) to connect it directly to S0. This won't work being at Node-2.

Analyst

I was referring to the number of available ports on Node 3 depeding on where it is placed, not ISS in general.

I didn't know that S0 carried the umbilicals, so Node 1 port is the only place it can go. Thanks Analyst :)

Offline dwb0407

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Re: Racks and Rack Positions
« Reply #76 on: 03/16/2009 01:55 PM »
A thanks from me too. The umbilicals was the piece I was missing in my head.

I had also (quite unnecessarily) X'd out node 1 nadir because of MRM-1. However now that I go back and look at it all, docking is the problem, the much slower process of berthing should be ok in the location.

Don

Offline hensleyd

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Re: Racks and Rack Positions
« Reply #77 on: 08/10/2013 09:38 PM »
I know this was a Racks and Rack Positions thread, but a lot of discussion between Space Pete, Herb and others was made as to the configuration of the CBM connections in the vestibule.

Are there diagrams or images available of the connection configs between the existing modules?

Thanks in advance, Darren Hensley.
Darren L Hensley

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