Author Topic: Docking ports for new modules  (Read 2777 times)

Offline Political Hack Wannabe

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Docking ports for new modules
« on: 03/06/2018 06:46 PM »
Ok, so when we see concepts for commercial modules that would be attached to ISS, if its a larger module (more BA-330 than BEAM, if you will), it is attached to the Forward port on the Harmony node.  Additionally, in my discussions with people involved in commercial station projects, a lot of them suggest there is only 1 usable port (which I am going to assume is that port - if not, please correct my understanding)

However, I know that there are docking ports on the Russian side - at Rassvet and Zvezda. 

Why aren't these ports part of the discussion?  I understand that there is a political and financial component to using these ports, but is there a technical  portion?  Or is there some other associated reason they aren't considered? 

I know that you'll still need places for Progress and Soyuz to dock, but (and I will admit this may be faulty understanding on my part) I thought a lot of the designs had the ability to pass through the modules (IE ports on both sides)

So, what am I missing?
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Online eeergo

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Re: Docking ports for new modules
« Reply #1 on: 03/06/2018 10:47 PM »
Ok, so when we see concepts for commercial modules that would be attached to ISS, if its a larger module (more BA-330 than BEAM, if you will), it is attached to the Forward port on the Harmony node.  Additionally, in my discussions with people involved in commercial station projects, a lot of them suggest there is only 1 usable port (which I am going to assume is that port - if not, please correct my understanding)

However, I know that there are docking ports on the Russian side - at Rassvet and Zvezda. 

Why aren't these ports part of the discussion?  I understand that there is a political and financial component to using these ports, but is there a technical  portion?  Or is there some other associated reason they aren't considered? 

I know that you'll still need places for Progress and Soyuz to dock, but (and I will admit this may be faulty understanding on my part) I thought a lot of the designs had the ability to pass through the modules (IE ports on both sides)

So, what am I missing?

There are four Russian docking ports. Apart from the restriction the small diameter ports bring with them (inability to pass voluminous racks and equipment inside/outside through them), and the political/financial considerations you mention (including the remote possibility the RS is separated as an independent station), there's also the logistics part.

You need two Soyuz and at least a Progress on Station at any given time, which leaves only one open port. You could envision a situation in which another port is freed by having no Progresses for a bit of time, but it would require more scheduling shuffling than just using Harmony forward, which is only going to be used by US Commercial Crew craft.

Then, there's the issue of clearances and operational constraints: Zvezda aft cannot be used for permanent module additions since it has the ISS engines for reboosts, CAMs etc (it can be occupied by a Progress since its engines can be used instead). Pirs nadir will soon not exist and be replaced by Zvezda nadir, but only to be occupied by MLM nadir, which is where Prichal (Node module) will go. This will give up to 5 more ports, but one will be needed for spacecraft docking anyway and two others (forward and aft) are not expected to be installed as operational ports. Could be done, but longer haul. The other two ports are needed for the NEMs or other Russian proposals, in principle. Rassvet nadir will have, on the other hand, clearance issues with the Leonardo PMM, and perhaps other secondary equipment.

This leaves only Poisk zenith, which in principle could work, but would leave the RS without redundancy in case a port is unusable for any reason, plus curtail the ability to have a second Progress (needed when Nauka arrives and the RS crew goes back to 3).
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Re: Docking ports for new modules
« Reply #2 on: 03/06/2018 11:09 PM »
Leonardo clearance is no longer an issue since its on Tranquility forward now.

A new module addition could always include one or more additional passive ports on the other end though, to make up for the one it takes. On the Russian side though, probably only the ports currently occupied by Pirs and Poisk would be viable for that, because all the other ones (including Zarya nadir, if Rassvet were to be moved) use SSVP-G4000 ports, which are not rated for very heavy combined stacks to be mounted on them. Anything approaching the size of Zarya/Zvezda/Nauka would (especially with a visiting vehicle docked) be too heavy.

I do think it might be worth considering using Unity nadir for expansion though. Tranquility was originally planned to attach there (and could have hosted visiting vehicles docked/berthed on its nadir side), and Leonardo was on that port for a few years (but never hosted visiting vehicles, since it didn't have a second port anyway). Clearance with Rassvet would obviously eliminate B330 or Ixion/any other Centaur V-derivative from possibly attaching there, but something roughly the diameter of the existing USOS modules (Axiom, or perhaps duplicates of some of the LOP-G concepts) should be fine, and could probably support VVs

Offline centaurinasa

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Re: Docking ports for new modules
« Reply #3 on: 03/07/2018 08:26 AM »
...There are four Russian docking ports. Apart from the restriction the small diameter ports bring with them (inability to pass voluminous racks and equipment inside/outside through them), and the political/financial considerations you mention (including the remote possibility the RS is separated as an independent station), there's also the logistics part...

Offline Political Hack Wannabe

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Re: Docking ports for new modules
« Reply #4 on: 03/07/2018 01:22 PM »
I am looking for ports that could support BA 330s/Ixion size and Axiom, so the unity ones you mentioned are out. 

A new module addition could always include one or more additional passive ports on the other end though, to make up for the one it takes. On the Russian side though, probably only the ports currently occupied by Pirs and Poisk would be viable for that

This is what I am wondering about.  What are the technical issues that are preventing this?  Or is it mostly financial and political? 
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Offline Cherokee43v6

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Re: Docking ports for new modules
« Reply #5 on: 03/07/2018 02:03 PM »
When you're talking a 'commercial' module, financial is actually a large component.  The ISS is built on two different standards.  The US standard and the Russian standard.

To mate to the Russian side, docking ports would have to be built to the Russian standard, which would restrict visiting vehicles to either Russian equipment or to have special adapters built to enable mating with the Russian equipment.  (Note the plural here since there would certainly be a requirement that the module allow for a Russian Standard visiting vehicle port on the opposite end of its attachment point.)

Unless the specific customer was willing to pay the premium to develop and build the adapter, or that customer was going to solely use Russian vehicles for access, then it would seem unlikely that the Russian side would be a viable host site for commercial modules.  Particularly if the ISS were being used as a host site for fitting out and validation testing for a free-flying station.
« Last Edit: 03/07/2018 02:04 PM by Cherokee43v6 »
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Offline erioladastra

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Re: Docking ports for new modules
« Reply #6 on: 03/20/2018 02:53 AM »
When you're talking a 'commercial' module, financial is actually a large component.  The ISS is built on two different standards.  The US standard and the Russian standard.

To mate to the Russian side, docking ports would have to be built to the Russian standard, which would restrict visiting vehicles to either Russian equipment or to have special adapters built to enable mating with the Russian equipment.  (Note the plural here since there would certainly be a requirement that the module allow for a Russian Standard visiting vehicle port on the opposite end of its attachment point.)

Unless the specific customer was willing to pay the premium to develop and build the adapter, or that customer was going to solely use Russian vehicles for access, then it would seem unlikely that the Russian side would be a viable host site for commercial modules.  Particularly if the ISS were being used as a host site for fitting out and validation testing for a free-flying station.

Another factor is utilities.  On the USOS you have centralized computing and power management.  On the RS, each module is almost its own space craft (e.g., many come with solar arrays).  So you would also to have to have a significantly different module design depending on what segment you were docking/berthing to.

Offline cferreir

Re: Docking ports for new modules
« Reply #7 on: 04/05/2018 11:18 PM »
Another question: Why is the PMA (Pressurized Mating Adapter) so much smaller (and bent) compared to the CBM? I don't understand why they didn't keep the CBM size, after all the Dragon v.1 supports it so why couldn't the Starliner and Dragon v.2 support a similar diameter? Again, I am not disputing the need for the PMA just the fact that it is smaller in diameter than the CBM. Thanks.

Online DaveS

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Re: Docking ports for new modules
« Reply #8 on: 04/06/2018 02:10 AM »
Another question: Why is the PMA (Pressurized Mating Adapter) so much smaller (and bent) compared to the CBM? I don't understand why they didn't keep the CBM size, after all the Dragon v.1 supports it so why couldn't the Starliner and Dragon v.2 support a similar diameter? Again, I am not disputing the need for the PMA just the fact that it is smaller in diameter than the CBM. Thanks.
The PMAs are essentially adapters between the CBMs and the APAS-95 docking system developed by the Russians (APAS-95 is essentially an evolution of the docking system used by the ASTP Soyuz). APAS-95 was used by the shuttle orbiters to dock (not berth which requires a robot arm) to the infant ISS. The bend is to clear the forward fuselage of the orbiters while keeping the length of the PMAs down.
« Last Edit: 04/06/2018 02:11 AM by DaveS »
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Online brickmack

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Re: Docking ports for new modules
« Reply #9 on: 04/06/2018 03:43 AM »
I think the question was more "why not just have a single larger port design?". It would obviously be operationally easier and cheaper to develop if they only had one US port standard.

The problem there is Soyuz. APAS was designed for use with Soyuz, and early ISS concepts using Soyuz used only APAS, no probe and drogue ports. Soyuz is too narrow to support anything wider than that though.

Offline cferreir

Re: Docking ports for new modules
« Reply #10 on: 04/06/2018 03:19 PM »
Ahh, that answers my question and is what I thought. The bend is because of the shuttle (which doesn't exist) and the size because of the Soyuz (which is old). Sucks. They could be entering the ISS in style instead will need to shimmy in like its 1970.

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Re: Docking ports for new modules
« Reply #11 on: 04/06/2018 04:20 PM »
Ahh, that answers my question and is what I thought. The bend is because of the shuttle (which doesn't exist) and the size because of the Soyuz (which is old). Sucks. They could be entering the ISS in style instead will need to shimmy in like its 1970.
The CBM hatches are only 60" (1.524 m) across so APAS isn't that much smaller. The actual CBMs themselves are 80" (2.032 m) in diameter.
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Offline nacnud

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Re: Docking ports for new modules
« Reply #12 on: 04/06/2018 04:30 PM »
Roughly .5m2(APAS) vs 1.7m2(CBM)

APAS is 1/3 the area
« Last Edit: 04/06/2018 04:32 PM by nacnud »

Offline Jim

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Re: Docking ports for new modules
« Reply #13 on: 04/10/2018 01:23 PM »
Ahh, that answers my question and is what I thought. The bend is because of the shuttle (which doesn't exist) and the size because of the Soyuz (which is old). Sucks. They could be entering the ISS in style instead will need to shimmy in like its 1970.

There is no shimmying.  The hatches are wide enough.

Offline Ronsmytheiii

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Re: Docking ports for new modules
« Reply #14 on: 04/18/2018 05:51 AM »
Ahh, that answers my question and is what I thought. The bend is because of the shuttle (which doesn't exist) and the size because of the Soyuz (which is old). Sucks. They could be entering the ISS in style instead will need to shimmy in like its 1970.

The APAS size wasn't really a big deal, since the orbiter airlock hatch from the mid-deck was pretty much the same size. Any cargo needing a large hatch would just go in a module that would be removed from the shuttle's payload bay and be directly attached to the ISS, much easier anyhow.
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