General Question ISS Attitude Control

[huuchuan1113]

Hi,

I've had my fair share of ISS dockings now but I would like to know something. I know ISS has attitude control to keep station facing desired direction. In real missions, is attitude control being used to keep station stable during docking? Also, is this attitude control implemented in the ISS on Orbiter? Or should I use something like Attitude MFD to keep station more stable? I can dock without it, but I can't be sure if this is the right way or not.

 

[Zandy12]

That's actually a really good question given that in real life the ISS orbits the Earth with the truss segment always parallel to the horizon. In Orbiter, the default ISS doesn't have RCS or is properly aligned with a realistic attitude. I think it's because the ISS mesh is very old (dating back 2006ish) and hasn't been updated along with everything else, making it a legit and unfair problem for people who do want to dock with the ISS. Perhaps this should be fixed soon or a newer mesh should be released to solve this. You can edit the ISS's code and add RCS thrusters from there but I don't know how to do that. I'd prefer a fresh redesign of the Orbiter ISS more.

 

[turtle91]

We have a working CMG at least for Orbiter 2010. ("https://www.orbithangar.com/searchid.php?ID=5351")
According to the CMG-thread, this seems to be crashing in Orbiter 2016.
However, it is still used in recent ISS A-Z scenarios (check "https://www.orbithangar.com/searchid.php?ID=7194").

So maybe you need to install ISS A-Z plus all it's dependencies to make it work in 2016...

 

[Donamy]

CMG will work in Orbiter2016, but you can't press F1 for the menu list or it will crash. You can still control it "blind" though. Look at the readme in the docs, for the right buttons. The Author is needed to recompile it, for it to work properly in Orbiter2016.

 

[turtle91]

>CMG will work in Orbiter2016, but you can't press F1
Now you can:

Ok, I have just recompiled the CMG2 for Orbiter 2016(source coded was provided in the original package by Poscik) and included the missing mesh(by C3PO).

There is also a test scenario using default ISS.
Before testing, I would suggest to make a backup of your original CMG2.dll.

It runs fine in my Windows 7 setup, but crashed in Wine when using D3D9-client (...like many other addons, which worked fine using D3D9 in Orbiter 2010(Wine, too), but no way to have them stable in Orbiter 2016...however...different story....).

Could someone please check this ?
The HUD should work now without CTD (...and without WINE)

 

[Donamy]

Works for me in D3D9-client(without wine) and regular. Hard to read the letters on the right, they are cut-off.

 

[turtle91]

>Hard to read the letters on the right, they are cut-off
Thanks for testing :thumbup:
The problem with the HUD has been reported within CMG2's thread, too.
So it's a general problem, even in Orbiter 2010.
Changing desktop/window resolution to i.e. 1024*768 "solved" the problem.

I will check, if I am able to change this, but I am not a developer...so...let's see.
Will check this tomorrow.

 

[ADSWNJ]

Hi,

I've had my fair share of ISS dockings now but I would like to know something. I know ISS has attitude control to keep station facing desired direction. In real missions, is attitude control being used to keep station stable during docking? Also, is this attitude control implemented in the ISS on Orbiter? Or should I use something like Attitude MFD to keep station more stable? I can dock without it, but I can't be sure if this is the right way or not.

The simplest thing to do is to switch to the ISS (F3, select ISS), and then either zero the rotations using the scenario editor (F4), or apply an orientation mode - e.g. ProGrade.

AFAIK, the vessel will have a natural gravity centric orientation similar to a tidal lock. So the IIS is probably fairly stable in a docking scenario, but I would expect it to free drift at the final moment, to let both vessels dock and react to each other without excessive torque.

No expertise here, but I wrote the RV Orientation MFD, so alignment in 6 degrees of freedom fascinated me for a long time though the writing of my MFD. Trying to dock to a dock rotating in multiple dimensions around a CoG is borderline impossible!

 

[boogabooga]

I think that there is a feature to auto-orient the ISS in this:

[ame="https://www.orbithangar.com/searchid.php?ID=5866"]PursuitMFD 2016[/ame]

Also, IIRC, in Orbiter 2010 the UCGO ISS added an RCS makes the ISS a selectable vessel.

 

[Zandy12]

>CMG will work in Orbiter2016, but you can't press F1
Now you can:

Ok, I have just recompiled the CMG2 for Orbiter 2016(source coded was provided in the original package by Poscik) and included the missing mesh(by C3PO).

There is also a test scenario using default ISS.
Before testing, I would suggest to make a backup of your original CMG2.dll.

It runs fine in my Windows 7 setup, but crashed in Wine when using D3D9-client (...like many other addons, which worked fine using D3D9 in Orbiter 2010(Wine, too), but no way to have them stable in Orbiter 2016...however...different story....).

Could someone please check this ?
The HUD should work now without CTD (...and without WINE)

Hey turtle91! The recompiled CMG2.dll file is for the Project Alpha ISS mesh included by default in Orbiter 2016 right??

 

[Donamy]

Works with ISS A2Z perfectly.

 

[turtle91]

>The recompiled CMG2.dll file is for the Project Alpha ISS mesh included by default in Orbiter 2016 right??

No, it works for any vessel/station which has a docking-port (the CMG needs to be docked....attachments are not working for this purpose).
However, to make testing for non-ISS-AZ-folks easier, I have provided a scenario, using the default stock ISS (Project Alpha).

>Works with ISS A2Z perfectly
That's great to see. Again, tomorrow I will check for the HUD, to make it more human-readable...

 

[Zandy12]

OK. Yeah I just tested that scenario everything looks good and is working well though the ISS is facing wrong direction but thats a problem with the docking port locations on the default ISS not the CMG. HUD is bit cluttered though. Also can you upload that on Orbit Hangar when you've debugged it please? Thank you!

 

[turtle91]

Ok, I have changed the display layout, so it should work on whatver-display-settings.
I tried to upload to OH, but got 504-gateaway-server-timeout-error.
Will try to upload the package tomorrow again.

EDIT:

tried it again, got an "someone has allready uploaded the same....." error message.
Not sure, if my previous attempt went through, even with 504 error message.
So...maybe the upload waits for approval.

This was my first upload to OH....had not expected so much trouble.
If this will not work, I will upload the package to this thread within the next days....the forum seems to be more reliable...

 

[francisdrake]

I think to remember a call from a Soyuz docking: "Ok, station is in free drift now." I guess attitude control is inhibited shortly before docking, to avoid sudden jolts of the station ruin an otherwise perfect approach.

Me using mainly default Orbiter MFDs I usually killrot the ISS before docking. If it keeps flying parallel to the horizon it slowly rotates following the Earth curvature, which is not very well supported by the default docking MFD.

 

[IronRain]

I think to remember a call from a Soyuz docking: "Ok, station is in free drift now." I guess attitude control is inhibited shortly before docking, to avoid sudden jolts of the station ruin an otherwise perfect approach.

Not only for Soyuz, but also for the shuttle.

https://en.wikipedia.org/wiki/Free_drift
http://blogs.esa.int/orion/2013/10/28/whats-happening-in-todays-undocking/

 

[Snax]

So this explains why I had difficulties to dock with the Shuttle with SSU while it wanted to keep the attitude I gave him with PRO201.

I thought they'd keep the same attitude even during the docking sequence.

[ame="https://www.youtube.com/watch?v=y5kmljwy-UQ"][Orbiter] ISS Final Approach & Dock #1 (day) - YouTube[/ame].

Well even though docking is difficult, it's like air refueling, difficult but not impossible !