ISS Orientation During Docking

[pete.dakota]

Space Shuttles make their final approach along the ISS 'v-bar' with the Earth 'underneath' the stack. However for the Earth to be 'under' the ISS and Shuttle throughout the entire docking then surely the ISS is very slowly rotating in the same manner that 'level horizon' would rotate a ship in LEO in Orbiter. This must mean the Shuttle also has to match the ISS's rotation in order to make a successful docking. Only after the docking the ISS and Shuttle stack is in 'free-drift' (or at least announced to be) to dampen out any motion between the two craft.

Using Orbiter I set up the ISS in the same orientation as in real life and then set the 'level horizon' AP. I rendezvoused with the station in the Shuttle and attempted to dock. It was very hard. As the ISS is constantly rotating under command of the AP, I had to be constantly adjusting the rotation of the Shuttle to keep everything white in the docking MFD.

Is the ISS placed into free drift before the Shuttle starts it's final approach? It's only announced by the ISS commander after the docking has occurred.

Is there any official documentation on this topic that is available?

 

[FordPrefect]

Using David413's ISS fleet you simply engage the prograde autopilot to orient the ISS in a realistic approach and docking orientation. While approaching the ISS on the v-bar, adjust your pitch rate close to -0.07 deg/s to keep yourself aligned with the v-bar.
I believe the free-drift mode is only engaged after the moment of phyiscal contact.

 

[pete.dakota]

Using David413's ISS fleet you simply engage the prograde autopilot to orient the ISS in a realistic approach and docking orientation. While approaching the ISS on the v-bar, adjust your pitch rate close to -0.07 deg/s to keep yourself aligned with the v-bar.
I believe the free-drift mode is only engaged after the moment of phyiscal contact.

That makes sense. Is the Shuttle's pitch rate achieved by manual firing on the thrusters, or does a computer perform it? And is there an MFD that can accurately show rotation rates?

I would like my dockings to be as realistic as possible.

 

[jungzimm]

If your'e using David's Fleet, the GPCMFD (I believe its OPS 2) has a screen that shows it. If your'e using Space Shutlle Ultra, OPS 201 shows the same information. If you're using stock Shutlle Atlantis, you can download the Univeral Pointing MFD from OrbitHangar and get the same info of it it. Current Rates for Pitch, Roll, and Yaw show up in bottom right corner of all 3 mfd's mentioned above. Just manually adjust your pitch till it's 0.07. It is a bit more of a chllenge but goes easier if you follow the Tutorial included with David's stuff. Happy docking.

 

[myles]

Attitude MFD rocks, I think! For me I can Time warp VERY high with it on!

http://orbithangar.com/searchid.php?ID=3165

 

[tblaxland]

Once you arrive on the v-bar, you can use AttitudeMFD to hold the orientation with the station. You will need to use Velocity mode, not Target Relative mode (Target Relative mode will line you up with the ISS centre of gravity instead of the docking port). Once in Velocity mode, set a pitch offset of +90 degrees and activate HOLD. Then use your linear thrusters to proceed in for docking.

I think attitude is controlled manually by the commander during real shuttle dockings but remember that they approach much slower in real life than most of us do in Orbiter.

 

[pete.dakota]

Once you arrive on the v-bar, you can use AttitudeMFD to hold the orientation with the station. You will need to use Velocity mode, not Target Relative mode (Target Relative mode will line you up with the ISS centre of gravity instead of the docking port). Once in Velocity mode, set a pitch offset of +90 degrees and activate HOLD. Then use your linear thrusters to proceed in for docking.

I think attitude is controlled manually by the commander during real shuttle dockings but remember that they approach much slower in real life than most of us do in Orbiter.

OK, I used attitudeMFD to show me the rates, and it worked well. It was a bit tricky setting the pitch rate to 0.07 using my joystick, but I was able to do it and the docking went perfectly.

I tried using AttitudeMFD to hold the correct attitude for docking . In theory, it could work perfectly, but, of course, it doesn't . Eyeballing docking MFD I manually set the values in AttitudeMFD for perfect rotational alignment. The MFD, though, doesn't know that I'm docking to something and so is constantly making small corrections which throws the translational alignment out of line, requiring constant manual corrections all the way up to contact. It's actually easier to do it manually.