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Old 02-22-2019, 08:40 AM   #91
indy91
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Originally Posted by Gingin View Post
 The APS secondary constraint will try to match both line of apsides?
Nope, it constraints the maneuver to happen at the next (or 5th or 10th or whatever) apsis, so either apoapsis or periapsis.

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Where do you find data on STS mission like the one we have on STS 130 in the rendez vous history book ?
Not in that format unfortunately, but I found the mission reports for all Shuttle missions on L2. A lot of them seem to be out there publically though, not sure if all. And I just took the time of ignitions for all the OMS and RCS burns and derived from that e.g. how many orbits there were between two burns. Takes some trial and error to get it right, but it works. If you don't have the mission reports then I'm sure you can still find the TIGs of all the burns somewhere online, at least for the last few years of Shuttle missions.

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To force it on a Perigee, is it PEO=1.0 ?
It's PER, not PEO.

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Originally Posted by Gingin View Post
 Alright, With fine tunning, it works better
So far, it gives me a rendez vous time as close as 2 mn compared to the real mission.

Really powerful tool, and so many way to shape our rendez vous.
Awesome work


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Some notes on this. I wouldn't fix the TIG for MC4, at least not this early on. That can cause a bunch of issues. It should be a DT from TI to MC4 of 000:01:16:54, that's the usual value. The last TIG that should be fixed is NC-4 or, if it exists in the plan, a NH burn that happens 0.5 revs before NC-4. That's all you need to move the terminal phase of the rendezvous around to achieve the right lighting conditions. EDIT: Ah, and that's why the earlier versions of the plan probably didn't work, because you had set e.g. the NPC maneuver to happen at 1 second of mission elaspsed time and not one second after the previous maneuver. There probably should be an error if it finds the TIG of a maneuver to happen before the previous maneuver.

Then, only a 4.45 ft/s plane change burn? That is very nice. Are you using spherical or nonspherical gravity? Did you use a TLE for the ISS or did you modify its orbit? And did you launch on time or changed that?

And lastly, I am confused about the rendezvous profile in general and how it can work. NC-2 is supposed to be a NH type maneuver, but it happens at apogee. So it can't really control the delta height. Well, it might be able to if the orbits are very elliptical and just changing the phasing would have an effect on the DH. I know the evaluation table in the History of Shuttle rendezvous document says that NC-1 is a NC maneuver and NC-2 is a NH maneuver, but in the relative motion plot it seems more like it's the other way around. Very weird.

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Could explain me how to use DES button to erase a secondary constraint ?
Ah yeah, I forgot to make that self descriptive. I'll add that to the input box. The format is: "Maneuver Secondary". So to delete the 4th secondary constraint of the 2nd maneuver in the table you need to input "2 4".

Last edited by indy91; 02-22-2019 at 08:52 AM.
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Old 02-22-2019, 10:08 AM   #92
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it constraints the maneuver to happen at the next (or 5th or 10th or whatever) apsis, so either apoapsis or periapsis.
Ok, good
I finally found the 3 rd part of FDO Handbook on L2.
Really interesting.
So much people and Docs around Nasa Programms, quite fascinating.




Quote:
the NPC maneuver to happen at 1 second of mission elaspsed time and not one second after the previous maneuver.
Yep, I put a T instead of DT in Threshold.



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Then, only a 4.45 ft/s plane change burn? That is very nice. Are you using spherical or nonspherical gravity? Did you use a TLE for the ISS or did you modify its orbit? And did you launch on time or changed that?

Spherical, I will try with non though and nodal precession, more fun and realistic

I created a flight plan to fit the ISS state vector at time of launch ( Sma and Ecc, and Mean Longitude to have the correct phasing)

I launched 300 sec before the DN. I found that in Orbiter and with SSU, it is the sweet spot.
It gave me Rinc of 0.01 ( never above 0.05)

I guess with nodal precession, it is better to have a more eastward LAN to catch up ISS LAN later and decrease the NPC at PC burn.


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And lastly, I am confused about the rendezvous profile in general and how it can work. NC-2 is supposed to be a NH type maneuver, but it happens at apogee. So it can't really control the delta height. Well, it might be able to if the orbits are very elliptical and just changing the phasing would have an effect on the DH. I know the evaluation table in the History of Shuttle rendezvous document says that NC-1 is a NC maneuver and NC-2 is a NH maneuver, but in the relative motion plot it seems more like it's the other way around. Very weird.
Yes, I do agree. It is surprising compared to what we are used to ( like your STS 114), whom I more familiar with.

I think in their philosophy, it is depicted as NH because it is the last burn ( except the EXDV which is more an over phasing protection burn than a proper phasing burn) before the final NC burn to set up SOI/R.

But with that Rendez vous profile, NH burn happens indeed quite early on.



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Quote:
Ah yeah, I forgot to make that self descriptive. I'll add that to the input box. The format is: "Maneuver Secondary". So to delete the 4th secondary constraint of the 2nd maneuver in the table you need to input "2 4".
Great, thanks
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Old 02-22-2019, 10:12 AM   #93
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That would be awsome to have the plot motion, I am really fascinating by those plot.
I love the one with Y on abcissa and Z on ordinate



EDIT: I tried the scenario with non spherical and nodal prec.
It is Ok ish excpet for the NPC
Really need to launch on an east ward Lan or In plane plus something
Need to quantify that now

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Just to make sure, the NPC with a 0 WEDG constraint at Ti will planify a burn to null the delta Y at Ti ?

Last edited by Gingin; 02-22-2019 at 10:53 AM.
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Old 02-22-2019, 11:00 AM   #94
indy91
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Quote:
Originally Posted by Gingin View Post
  I tried the scenario with non spherical and nodal prec.
It is Ok ish excpet for the NPC
Really need to launch on an east ward Lan or In plane plus something
Need to quantify that now
For me it worked out great when I used an ISS state vector from TLE and hoping that the Shuttle launch time is at the in-plane time. If that is the case then the trajectories should be very close to reality and thus give small NPC burns.

I think there actually should be 9.5 orbits between NC-1 and NC-2, not 9.0. And I tried making NC-1 the NH burn and NC-2 the NC burn. The problem with such an early NH type burn is that it has a big influence on the phasing, so it shifts the time at which the DH constraint is applied (the TI manevuer). And that causes it to iterate very badly. The orbits are elliptical and the line of apsides aren't aligned yet.

I wonder if the fix for that is the lighting constraint "NITI = -28" that the basic, TIG-less rendezvous plans seem to have. That basically keeps the TIG for the constrained maneuver fixed, because the lighting is based on the target orbit, not the Shuttle one. I think I'll implement those lighting constraints and will see, if that improves the behavior of the early NH burns. Of course after the initial plan is working, more TIGs are fixed and varied to get the lighting and TI DVZ even more right. And the NH iteration probably prefers fixed TIGs.

Quote:
Just to make sure, the NPC with a 0 WEDG constraint at Ti will planify a burn to null the delta Y at Ti ?
Yes, it will try to make the orbital planes of both vehicles the same at the time of the TI maneuver.
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Old 02-22-2019, 11:19 AM   #95
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I used an ISS state vector from TLE
What is TLE ?
With trial and error, I think around 0.15 of diff between Lan after MECO gives great results for that type of Rendez Vous.
Almost there for the full mission


Quote:
I think I'll implement those lighting constraints and will see, if that improves the behavior of the early NH burns. Of course after the initial plan is working, more TIGs are fixed and varied to get the lighting and TI DVZ even more right. And the NH iteration probably prefers fixed TIGs.

Very nice. There are indeed a lot of Lighting Constraint in the book
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Old 02-22-2019, 11:25 AM   #96
indy91
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Originally Posted by Gingin View Post
 What is TLE ?
Two-Line Element set. And there is an addon for Orbiter called "Scenario Editor TLE", which can convert such a TLE to a state vector in Orbiter. That's probably the best way to get a realistic orbit for the ISS.
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Old 02-22-2019, 11:52 AM   #97
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Nice.
Do you know in which format as to be the TLE file to Load it through Load TLE in Scanario editor?
You took them from here: https://www.space-track.org/auth/login ?

Last edited by Gingin; 02-22-2019 at 11:54 AM.
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Old 02-22-2019, 11:58 AM   #98
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Originally Posted by Gingin View Post
 Nice.
Do you know in which format as to be the TLE file to Load it through Load TLE in Scanario editor?
You took them from here: https://www.space-track.org/auth/login ?
Current TLEs and (not-recent-enough-) Archive.
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Old 02-22-2019, 01:35 PM   #99
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Thanks GLS.



Alright, I think I finished with STS 130 with spherical Gravity

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I am working on non spherical now.
A bit more tricky, a difference of 0.12 in Lan after Meco seems to work well, with a NPC of 15 fps max
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