OHM Crew Dragon for Orbiter2016

Donamy

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It doesn't matter where the ISS is. It's where the orbital track line is.
 

Kinga

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Thanks for that Brian but I'm definitely using your original scenario without changing the MJD date. Date and Time in top left corner say 27th May 20:30:40 2020.

I DID try using your original scenario and changing the Date first though. And then I went back and re-copied and pasted your original text. Could that first attempt have screwed up something permanently somehow (though I can't work out how since it's showing Scenario Correct date and time)

But the second scenario you posted for 30th May is bang on the money anyway.

I'll check out the Scenario Editor. Is that a separate add on?
 

BrianJ

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Thanks for that Brian but I'm definitely using your original scenario without changing the MJD date. Date and Time in top left corner say 27th May 20:30:40 2020.

I DID try using your original scenario and changing the Date first though. And then I went back and re-copied and pasted your original text. Could that first attempt have screwed up something permanently somehow (though I can't work out how since it's showing Scenario Correct date and time)

But the second scenario you posted for 30th May is bang on the money anyway.

I'll check out the Scenario Editor. Is that a separate add on?
Hi,
as Donamy says above - roughly speaking, the position of ISS along it's orbit is not what determines the launch window (although it does determine how long it will take to rendezvous once in orbit, and what strategy you use to get there).

The launch window is determined by when the ISS orbit plane passes overhead at the launch site (actually a few minutes before that, since your spacecraft will take a few minutes to reach orbit).

If you take a look at your MapMFD for each of the scenarios for 27th and 30th, you can see that the ISS orbit plane is in the same place relative to KSC at the liftoff time.

ScenarioEditor is packaged with Orbiter, enable the "ScnEditor" module on your OrbiterLaunchpad "Modules" tab, then you can press Ctrl+F4 during sim and select "ScenarioEditor" from the dropdown list. It's very useful!

Hope this helps :)
Brian
 
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Donamy

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Also, check out some videos on you tube by David Courtney.
 

Kinga

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I know about the track. That’s what I’m saying; in the scenario for the 27th, copied directly from your post, the track for the ISS does not pass over KSC. I just mentioned the fact that the ISS is over Turkey to add further information.

If I can work out how to insert a screen shot I’ll show you.
 

insanity

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I know about the track. That’s what I’m saying; in the scenario for the 27th, copied directly from your post, the track for the ISS does not pass over KSC. I just mentioned the fact that the ISS is over Turkey to add further information.

If I can work out how to insert a screen shot I’ll show you.
You can always wait! The earth is spinning under the ISS as the ISS is moving so at some point the orbital path of the ISS will align with KSC. With some judicious use of time acceleration ('t' to speed up and 'r' to slow down), you'll find a good launch window.

You can see the time to node in the align planes MFD and plan to go when the time to the descending node (DN) is ~ 330 seconds. The lovely autopilot should fly the northeastern launch track and put you into orbit in a low relative inclination to ISS.


Depending on where the ISS is, you'll determine your strategy for rendezvous.
 

Kinga

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Thanks Insanity. Understand that and I have done that. I've successfully rendezvoused with the ISS in my little Dragon capsules a few times now. I'm just trying to work out why in the scenario for the 307th the ISS is where it is supposed to be but in the one for the 27th it's not. I'm presuming when other people load up the scenario for the 27th, the ISS track is passing directly over KSC like it does in the scenario on the 30th. I think I've screwed something up but I'm not sure what.

---------- Post added at 01:35 AM ---------- Previous post was at 01:22 AM ----------

Hi Brian, I used your DM2 scenario but the ISS is way off. None of the three ground tracks go anywhere near KSC
(emphasis added) See, I'm not completely ignorant of orbital mechanics...(I'm very ignorant, but not completely)
 

BrianJ

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Thanks Insanity. Understand that and I have done that. I've successfully rendezvoused with the ISS in my little Dragon capsules a few times now. I'm just trying to work out why in the scenario for the 307th the ISS is where it is supposed to be but in the one for the 27th it's not. I'm presuming when other people load up the scenario for the 27th, the ISS track is passing directly over KSC like it does in the scenario on the 30th. I think I've screwed something up but I'm not sure what.

---------- Post added at 01:35 AM ---------- Previous post was at 01:22 AM ----------

(emphasis added) See, I'm not completely ignorant of orbital mechanics...(I'm very ignorant, but not completely)
Hi,
I'm guessing you see something like my screenshots below. Both images captured at T-10 from the scenarios for launch on 27th and 30th. Left MapMFD shows the "Ground Track", right MapMFD shows the "Orbit Plane". You can see that although the ISS Ground Tracks look different for the different launch dates, the ISS Orbit Plane is in the same place relative to KSC. It's the ISS Orbit Plane that you're aiming for (since aligning different orbit planes once you are in orbit requires considerably more dV than rendezvous in the same orbit plane). Could this be the source of confusion?
dm2_27.jpg
dm2_30.jpg
Cheers,
Brian
 

Kinga

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Hi Brian, yes your first screenshot is what I get. But now I'm really confused. Aren't we supposed to wait till the target track is over the launch site in order to make for the most efficient rendezvous? If I launch at the official launch time of the scenario, my plane is not aligned with the ISS. I end up with an orbit that has an Inc of 57.85 degrees while the ISS is 54.95 and the LAN is out too. Is that expected? Was I supposed to make manual adjustments during the launch using the first or second stage engines to better align the orbit? Or am I supposed to do the Align Planes after SECO?
 

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Donamy

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I believe the Crew Dragon does the plane changes, so the 2nd stage isn't left in the same orbital plane as the ISS. I could be wrong. Anyone know for sure ?
 

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Off topic.
I did read they are thinking about a second stage recovery.
 
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Kinga

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That's great information Donamy. Sounds like the Phase Burn was the Align Planes maneuver.

Sorry Brian I didn't even get what you were saying when you showed the different MFDs comparing ground track to orbital plane. I now need to Google "ground track vs orbital plane" because that's all new to me.

But if I launch when the ISS is on a ground track that is 1000kms to the west of me, my orbital plane might match the ISS but won't my LAN be 1000km different and I will have to spend a lot of fuel to align planes, to shuffle my LAN around till it matches the ISS?
 

francisdrake

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I have question on ISS docking: The ISS is in an horizon-hold attitude, so it rotates slowly to follow Earth's horizon. This makes the docking approach challenging, as the docking port rotates with it.

Do they kill the rotation of the 'real' ISS, before it goes into free drift?
 

BrianJ

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Aren't we supposed to wait till the target track is over the launch site in order to make for the most efficient rendezvous?
Hi,
generally speaking, you can wait until the Target "Orbit Plane" coincides (is "overhead") with your launch site.

If I launch at the official launch time of the scenario, my plane is not aligned with the ISS. I end up with an orbit that has an Inc of 57.85 degrees while the ISS is 54.95 and the LAN is out too. Is that expected? Was I supposed to make manual adjustments during the launch using the first or second stage engines to better align the orbit? Or am I supposed to do the Align Planes after SECO?
Yes, that's expected. Have a read of my comments in the posts containing the scenarios for reasons why. Yes, you need to do some steering with either the Upper Stage or the Dragon itself (or both!), in order to align planes with ISS.

Note: Remember orbit parameters can be expressed in either Ecliptic or Equatorial reference frames - Falcon9 control panel uses Equatorial. Also, Launch Azimuth is not equivalent to Inclination.

But if I launch when the ISS is on a ground track that is 1000kms to the west of me, my orbital plane might match the ISS but won't my LAN be 1000km different and I will have to spend a lot of fuel to align planes, to shuffle my LAN around till it matches the ISS?
If your orbital plane matches the ISS, you will have the same LAN and Inclination, by definition.


As a side note as to whether the "Align Planes" maneuver is performed by the Upper Stage or Dragon (or both) - there has to be some steering done by the Upper Stage for the ground track to pass over the Shannon abort zone, unless the Dragon makes a plane change burn immediately after separation. My hunch is that the Upper Stage does most of the Align Planes work. The first burn by the Dragon takes care of any residual error.

I saw the Dragon go over (low to the SW from here on UK S.Coast) about 20mins after launch, but I didn't see any sign of Upper Stage. So either the Dragon or Upper Stage had done some kind of maneuver within ~10 mins of Dragon separation. Maybe an Upper Stage de-orbit burn? Unless, of course, I just missed seeing the Upper Stage ;-)

Cheers,
Brian
 

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Hit an unexpectedly large wave while bringing the capsule back to the mainland. Not sure when we will be back...the GoSearcher has boldly gone...
 

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Donamy

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Hey Don just wondering if you got Pursuit MFD working with the Dragon capsule?


Mystery solved.


The HUD has to be ON for information to be used in PursuitMFD for the auto docking to work. I had the HUD off to de-clutter the screen for docking with the Generic camera. :facepalm:
 

CTarana45

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First Time For Earth Rockets! Downloaded both add-on's and had no trouble with them! Nice to night launches again! :thumbup::thumbup: I like the way Mr Musk is beating the Russians again! :rofl:

Thanks, Guys! :hailprobe:

Christopher Tarana
 
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