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Tutorial ORBITER Tutorial Series for Beginners: The Application of Orbital Mechanics

Tex

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This is a series of tutorials I'm working on which covers the application of orbital mechanics within ORBITER 2016 and includes an in-depth look at the various MFDs used for orbital maneuvers.

Part 1: The Orbital Elements

Part 2: Launch to Orbit & ISS Launch Windows

Part 3: Orbital Plane Alignment (Align Plane MFD)

Part 4: Sync Orbit & Rendezvous (Sync MFD)

Part 5: Docking with the ISS (Dock MFD)

I hope some find this series helpful in one way or another. I apologize it has taken me so long to complete this project, but I should have the last 3 videos completed soon!
 

Aeadar

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Hiya Tex!

I've only seen the first two of these and will have to wait til tomorrow for the third one since it's time for bed. But I have to say that the first two are just beautifully done! All the important points in a concise and perfectly clear presentation.

Very, very nicely done, and fun to watch!:tiphat:


:cheers:
 

Matrix Aran

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They're really great videos Tex, and the do a great job of illustrating the major concepts that one needs to understand to dock with an orbiting vessel. Being just a bit critical, I think the first video starts off with a little bit of information overload, as it describes a lot about orbit orientations and inclinations all at once, but sticking with the videos everything becomes very clear in time.

It was the only time in all three videos that I found the information overwhelming, the rest of the time everything was quite clear.

I've seen that video you're referring to, and the description shows up in a lot of physics textbooks as well. The problem is the demonstration relies on an absurdly high mountain to help illustrate what is an orbit.

To represent it with a launch, I'd suggest using greatly exaggerated suborbital launches, so the viewer can see the ship arc up off of the earth and fall back down. As you add horizontal velocity, it would become more and more apparent how the arc will "fall over the edge of the earth" and arc back around. If you can show this all in one shot it might be more apparent just how much of an effect horizontal velocity has.

When it comes to launch windows, Map MFD usually illustrates them quite clearly, though I'm not sure how to illustrate the other conditions the NASA video brought up, should you want to cover any of them.
 

martins

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Hi Tex,

this is an excellent idea! The videos a probably easier to grasp for a lot of people than a dry description in a manual. Maybe this could be turned into some sort of "official" Orbiter tutorial, possibly even with exercise scenarios to go with ("you've seen the video, now try for yourself").

I've gone through the first video so far - will do the others next. Two small niggles I noticed:

  • The orbit at the beginning of the video isn't equatorial. An equatorial orbit should pass over northern South America, not over central America (and Cuba by the end of the sequence). Your orbit appears to be zero inclination wrt. eclicptic, not equator. Later you show a zero inclination indication in the Orbit MFD. Was that for ecliptic or equatorial frame of reference? Also after rotating to a polar orbit, I suspect this didn't pass over Earth's poles, but ecliptic poles.
  • The ascending and descending nodes (AN and DN) in the Align Planes MFD are not wrt. the equatorial plane, but wrt. the orbital plane of the target object. This is the reason why the alignment burns take place at these points - the positions coincide there, and all that is required is a (tangential) change in velocity. The reason this happened to work out in your example is because the two orbital planes crossed approximately over the equator, according to the Map MFD, but this was a coincidence.
 

Tex

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To represent it with a launch, I'd suggest using greatly exaggerated suborbital launches, so the viewer can see the ship arc up off of the earth and fall back down. As you add horizontal velocity, it would become more and more apparent how the arc will "fall over the edge of the earth" and arc back around. If you can show this all in one shot it might be more apparent just how much of an effect horizontal velocity has.
Thanks for your feedback. I especially like this idea. I'll see what can be done about showing both together.


Hi Tex,

this is an excellent idea! The videos a probably easier to grasp for a lot of people than a dry description in a manual. Maybe this could be turned into some sort of "official" Orbiter tutorial, possibly even with exercise scenarios to go with ("you've seen the video, now try for yourself").

I've gone through the first video so far - will do the others next. Two small niggles I noticed:

  • The orbit at the beginning of the video isn't equatorial. An equatorial orbit should pass over northern South America, not over central America (and Cuba by the end of the sequence). Your orbit appears to be zero inclination wrt. eclicptic, not equator. Later you show a zero inclination indication in the Orbit MFD. Was that for ecliptic or equatorial frame of reference? Also after rotating to a polar orbit, I suspect this didn't pass over Earth's poles, but ecliptic poles.
  • The ascending and descending nodes (AN and DN) in the Align Planes MFD are not wrt. the equatorial plane, but wrt. the orbital plane of the target object. This is the reason why the alignment burns take place at these points - the positions coincide there, and all that is required is a (tangential) change in velocity. The reason this happened to work out in your example is because the two orbital planes crossed approximately over the equator, according to the Map MFD, but this was a coincidence.
Thanks Martin, shows I still have much to learn myself. I would definitely like to get this right, so I need to grasp the corrections you've produced for me here so that I can go back and fix the videos. I always hate to upload any videos before I finish them, but in this case I desperately needed feedback to get these right this time. If I can do that, it would be awesome to have them as official tutorials. Having scenarios to go with them would be an added bonus. :cheers:
 

Tex

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  • The orbit at the beginning of the video isn't equatorial. An equatorial orbit should pass over northern South America, not over central America (and Cuba by the end of the sequence). Your orbit appears to be zero inclination wrt. eclicptic, not equator. Later you show a zero inclination indication in the Orbit MFD. Was that for ecliptic or equatorial frame of reference? Also after rotating to a polar orbit, I suspect this didn't pass over Earth's poles, but ecliptic poles.
To answer your specific questions (I forgot to do above)... I used the scenario editor to change the inclination, so I guess that's why it was with relation to the ecliptic and not the equator. I will have to fix that for sure. For the clip in which I show the inclination on the Orbit MFD, the reference frame was indeed set to ecliptic (I just checked now).


  • The ascending and descending nodes (AN and DN) in the Align Planes MFD are not wrt. the equatorial plane, but wrt. the orbital plane of the target object. This is the reason why the alignment burns take place at these points - the positions coincide there, and all that is required is a (tangential) change in velocity. The reason this happened to work out in your example is because the two orbital planes crossed approximately over the equator, according to the Map MFD, but this was a coincidence.
I didn't realize that, I thought all this time it was with relation to the equator. I will have to fix that too. :facepalm:
 

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Hi Tex.
Excellent stuff from you, as usual (after those small corrections it'll be awesome!)

For those external views of the Earth, is it just Orbiter and Videnie?

Reading Matrix Aran's suggestion, I thought of this image (or many other of that kind) where one can "see" where you start adding horizontal speed in order not to fall down:

 

martins

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To answer your specific questions (I forgot to do above)... I used the scenario editor to change the inclination, so I guess that's why it was with relation to the ecliptic and not the equator. I will have to fix that for sure. For the clip in which I show the inclination on the Orbit MFD, the reference frame was indeed set to ecliptic (I just checked now).
In the scenario editor, you have a choice to specify the orbital elements either in the ecliptic or the equatorial frame. Default is ecliptic. To switch to equatorial, set the "Frame" option to "ref. equator". If you then set the inclination to 0, you will get an equatorial orbit.
Likewise, the Orbit MFD can be switched to equatorial readouts by clicking the "FRM" button. The "Frm" indicator in the top right corner should then switch from "ECL" to "EQU".

I didn't realize that, I thought all this time it was with relation to the equator. I will have to fix that too. :facepalm:
No problem - you live and learn with orbiter :thumbup:

I watched the other two tutorials now - very nice indeed! I didn't spot any obvious problems there, but I'll have another go tonight. Keep them coming!
 

C3PO

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The ascending and descending nodes (AN and DN) in the Align Planes MFD are not wrt. the equatorial plane, but wrt. the orbital plane of the target object. This is the reason why the alignment burns take place at these points - the positions coincide there, and all that is required is a (tangential) change in velocity. The reason this happened to work out in your example is because the two orbital planes crossed approximately over the equator, according to the Map MFD, but this was a coincidence.
I think Tex confused the plane intersections with LAN.
 

Tex

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In the scenario editor, you have a choice to specify the orbital elements either in the ecliptic or the equatorial frame. Default is ecliptic. To switch to equatorial, set the "Frame" option to "ref. equator". If you then set the inclination to 0, you will get an equatorial orbit.
Likewise, the Orbit MFD can be switched to equatorial readouts by clicking the "FRM" button. The "Frm" indicator in the top right corner should then switch from "ECL" to "EQU".


No problem - you live and learn with orbiter :thumbup:

I watched the other two tutorials now - very nice indeed! I didn't spot any obvious problems there, but I'll have another go tonight. Keep them coming!
Thanks Martin, I was just playing with the scenario editor again and spotted my fault there. I just never realized that option to switch between them. :)

I'm churning ideas in my head of a better way to present this information along with a better overview of the Orbit MFD itself which I didn't really go into great detail about. At least it sounds like I got the syncronising orbits part right because that was a tough one to do! I had to refer to the manual for some of that terminology. :lol:
 

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At 5:30 on the 3rd video you say "I don't know which way it's gonna take yet, either translating forward or backwards..." but you know it in fact.

Since your Sh-ToR is higher than Tg-ToR, you must slow down, so: orient prograde and burn forward.

Edit: suddenly I'm not so sure about what I just said...
 
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C3PO

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At 5:30 on the 3rd video you say "I don't know which way it's gonna take yet, either translating forward or backwards..." but you know it in fact.

Since your Sh-ToR is higher than Tg-ToR, you must slow down, so: orient prograde and burn forward.

Edit: suddenly I'm not so sure about what I just said...
It depends on if you're going to use that particular orbit to do the rendezvous. In the video Tex has just passed the reference axis, and the ToR goes to 102.8K (seconds) for both craft. There's no way to tell who will arrive first, unless you calculate the time more accurately. If you forward one more orbit, you'd get one more digit.

T depends on your SMa, so if you want T to increase you need to add energy.
 
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ADSWNJ

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Great set of videos. Tex. All that time on those race bikes must be working up your appetite again for Orbiter and this community, which is great to see!

On the launch video - I would very much like to see you discuss why you don't just launch the DG vertically and go to 200 KM with zero orbital velocity. (Obvious, I know, but the graphical orbit view and showing the effects at hist speed time would be cool. Then show a ballistic sub-orbit, and then transition to the full orbit. (Of course - burn to your desired parking apogee height, MECO and cruise up to the apogee, then burn to circularize (with a demo of what happens if you forget the second burn!!).

The thing I was talking about in the MFD / TransX thread was the difference between sub-orbital velocity and orbital. Say you are flying from JFK to LHR in a plane. You would go great circle, all things being equal, as it would be least mileage. But often the flights go on a southerly routing to avoid winds / storms / etc. I was interested in the transition from say a constant latititude sub-orbital trajectory to an orbital trajectory. (I.e. flying at say a constant 50 degrees N, 090 heading (no wind), you describe a circle centered on the polar axis, but at 50N versus the center of gravity of the Earth. If you continue to add velocity, headed constantly 090, then you transition into an orbit with 50N / 50S extremes, and centered on the Earth's COG. Physically, that's an interesting transition, as the immense amounts of centripetal (inwards facing) and centrifugal (outwards facing) force take you clean out of your 50N circle into that orbit.

Anyway - if you go anywhere near showing this, you would be a hero!!

---------- Post added at 12:53 AM ---------- Previous post was at 12:45 AM ----------

One thing on the Orbit Sync video ... you could also add an Advanced Sync version for docking with elliptical targets. In this case, you need to think about aligning more of the orbital elements, so your Peri is at the same AgP as the target, and you bring your ApA and PeA to a close alignment with the target. The simple way to move the AgP is to get circular, and then open up into the elliptical orbit at the right point. To move the AgP forward and back, you need to do off-Apo/Peri burns (e.g. 30 degrees off) carefully nudging it!
 

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Hey, great job on the vids. I think your presentation is very clear and easy to understand. This will be helpful to the new orbinauts out there.
 

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...In the video Tex has just passed the reference axis, and the ToR goes to 102.8K (seconds) for both craft. There's no way to tell who will arrive first...
Exactly. When I saw both going to 102.8k my confusion started.
Ok, never mind...:facepalm:
 
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C3PO

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When I use SyncMFD I always wait until DTMin isn't last on the list. That way you know you have the orbit with the closest distance. I usually wait for orbit 10 to go yellow. Then I change LEN to 11 before making the adjustment.

Remember "0" is the current orbit.
 

Tex

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Thanks for all the feedback guys! Using the NASA orbital mechanics video, I have written up a new dialog for the first part of the video which will cover all six of the orbital elements and explain in greater detail the orbit MFD using specific examples. I will work on getting that done this weekend. Once I finish it, I'll remove the old video and upload the new and update this thread.
 

Tex

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No problem! If you liked these preliminary videos, wait until you see the final versions. I'm just about finished with the new part 1, but I'm working with Martin to ensure it's all correct before releasing it. Hopefully I can wrap it up within a day or two now.
 
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