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[old thread] Trajectories : atmospheric predictions

Youen

By Youen
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Youen

Youen

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The way I imagine it to work is, that while building my rocket I strip everything that's supposed to be decoupled before reentry from my capsule and hit a button "Save aerodynamic profile". Later on in flight then I would be able to tell the mod to use this saved profile instead of the profile FAR is currently reading, so the trajectory would actually match that of my next stage instead of the current one.

I think it should be possible to extract any stage during flight, by looking at the staging actions, and cutting parts of the vessel graph where things are going to decouple. I think Kronal Vessel Viewer does exactly this. The user could then be proposed a field to type the stage number than will reenter (by default the last stage?). But that would not help for manual things you are planning to do (such as decoupling docking ports before reentry, etc.)

Once this is done, the mod could simulate only the remaining parts. This could be slightly wrong for FAR that makes more complicated things (parts interact with each other, wing cross winds, etc.), but I don't know how inaccurate (or not) it would be.

In my opinion, such an automatic system would be better than adding more user interactions towith the mod. Otherwise, each time you change your ship design, you would have to click the "Save aerodynamic profile" again, which means you'd have to remove the staged parts first, click the button, and re-attach the parts. Also, if you forget to do it, you may get inaccurate results, not be able to fix it while in flight, and don't know if you have to blame the mod or yourself for forgetting an update. The developpers who get bug reports wouldn't know either ;-)

- - - Updated - - -

Squad should make this stock, as an "upgrade" to the piloting system of career mode. Amazing mod.

I agree they could (should?) do that for stock aerodynamics. The problem is that it wouldn't work for mods such as FAR. But they could probably give an API that would allow modders to plug their system in.

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helaeon

helaeon

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For the amazing shrinking predicted orbits on aerobraking on FAR issue:

Just switched to NEAR from FAR. Using NEAR the prediction is spot on. So, whatever is causing more drag to be experienced than expected is something that FAR is calculating that NEAR is not. No idea what that might be, but if predictions were working well for people in FAR pre .90, then it's one of the new features that's not being read in or accounted for.

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Postron

Postron

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I think it should be possible to extract any stage during flight, by looking at the staging actions, and cutting parts of the vessel graph where things are going to decouple. I think Kronal Vessel Viewer does exactly this. The user could then be proposed a field to type the stage number than will reenter (by default the last stage?). But that would not help for manual things you are planning to do (such as decoupling docking ports before reentry, etc.)

Once this is done, the mod could simulate only the remaining parts. This could be slightly wrong for FAR that makes more complicated things (parts interact with each other, wing cross winds, etc.), but I don't know how inaccurate (or not) it would be.

In my opinion, such an automatic system would be better than adding more user interactions towith the mod. Otherwise, each time you change your ship design, you would have to click the "Save aerodynamic profile" again, which means you'd have to remove the staged parts first, click the button, and re-attach the parts. Also, if you forget to do it, you may get inaccurate results, not be able to fix it while in flight, and don't know if you have to blame the mod or yourself for forgetting an update. The developpers who get bug reports wouldn't know either ;-)

Having the player plan ahead was actually part of my intention, since it would be unrealistic to be able to simulate even for configurations that weren't even intended for reentry, that being said right now the mod can simulate for any possible configuration as well as long as that configuration is actually physically (in game) present, so it would make sense to be able to simulate any stage from how the mod works right now.

That being said I believe FAR actually needs a craft to be physically present in the game in order to determine its aerodynamic behavior so if we wanted to auto predict for every stage we'd probably need to replicate the part of ksp.exe that turns a craftfile into an 3d KSP-ingame model, which is probably against the rules. Therefore it'd be far easier to save this aerodynamic behavior at that point of time when the configuration is actually present in game which will usually be while building the craft. (Usually you start to build your crafts from the top stage, don't you) Also regarding reattaching everything after stripping it of, you can just reload the finished craft provided you saved it earlier.

- - - Updated - - -

For the amazing shrinking predicted orbits on aerobraking on FAR issue:

Just switched to NEAR from FAR. Using NEAR the prediction is spot on. So, whatever is causing more drag to be experienced than expected is something that FAR is calculating that NEAR is not. No idea what that might be, but if predictions were working well for people in FAR pre .90, then it's one of the new features that's not being read in or accounted for.

In one of the last updates Ferram introduced an concept called Reynolds-Numbers which drastically increases drag in low pressure, high velocity situations. Therefore skimming through the upper atmosphere now alters the orbit far more than before.

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Kobymaru

Kobymaru

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For the amazing shrinking predicted orbits on aerobraking on FAR issue:

Just switched to NEAR from FAR. Using NEAR the prediction is spot on. So, whatever is causing more drag to be experienced than expected is something that FAR is calculating that NEAR is not. No idea what that might be, but if predictions were working well for people in FAR pre .90, then it's one of the new features that's not being read in or accounted for.

In one of the last updates Ferram introduced an concept called Reynolds-Numbers which drastically increases drag in low pressure, high velocity situations. Therefore skimming through the upper atmosphere now alters the orbit far more than before.

I love you guys! Predictions are actually perfect with NEAR. I will investigate this further, before any of the Staging talk if you don't mind. This has been bugging me for weeks now :)

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eightiesboi

eightiesboi

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Just tried this for the first time. Using NEAR and testing out a DERP, the prediction was off by a bit. As in, I landed on the wrong side of the planet. Started from a 100KM circular orbit, burned so that the red cross was right on top of the KSC. What did I do wrong?

Active Texture Management

Better Buoyancy

Blizzy's Toolbar

Chatterer

Community Resource Pack

Connected Living Space

Deadly Reentry Continued

Distant Object Enhancement

Docking Port Alignment Indicator

Final Frontier

Firespitter Core

Kerbal Alarm Clock

Kerbal Attachment System

Kerbal Construction Time

Kerbal Engineer Redux

KSP AVC

KSP Tips

Neophyte's Elementary Aerodynamics Replacement

No More Grind

Planet Shine

Precise Node

Procedural Fairings

Raster Prop Monitor

Real Chute Parachute Systems

Regolith

Remote Tech

SCANSat

Science Alert

Ship Manifest

Stage Recovery

Station Science

Thunder Aerospace Corporation's Life Support system

Trajectories

Transfer Window Planner

TriggerAu Flags

Umbra Space Industries Tools

Universal Storage

USI Survival Pack

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Kerbas_ad_astra

Kerbas_ad_astra

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Orientation can make quite a difference with FAR (and NEAR, I'm sure). The default value is prograde (0), while most pods come in retrograde. I've heard that -180 gives slightly better results than 180 (even though they should be the same, but this is a known issue).

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Kobymaru

Kobymaru

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Just tried this for the first time. Using NEAR and testing out a DERP, the prediction was off by a bit. As in, I landed on the wrong side of the planet. Started from a 100KM circular orbit, burned so that the red cross was right on top of the KSC. What did I do wrong?

Usually, this is an issue of wrong AoA settings. Trajectories can't (or rather won't) guess your flying, so you can set the AoA (or the pitch) in the descent profile. It defaults to 0°, but if you reenter with a single capsule and point retrograde, it should be -180°. Try that first.

Also, which versions of Trajectories and NEAR are you using?

Oh, and also wings dont work yet. If you have wings, your prediction will be wrong.

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Baythan

Baythan

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I didn't see anyone else bring this up, so: I noticed the download comes bundled with ModuleManager. Am I correct in inferring that that means this needs ModuleManager to work?

Yes. ALL mods that come bundled with ModuleManager do so because they require MM in order to function properly.

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Hektos

Hektos

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I am getting a NaN lockup when trying to launch a rocket, going in to map view and turning on trajectories.

The NaN error seems like it is coming from FAR, but upon removing Trajectories I no longer get the NaN lockup.

I have already posted this in the FAR thread, but it seems like this error is being caused by Trajectories.

Steps to reproduce:

1) Create any rocket with 4 R8 Winglets (My test rocket, all stock parts stock)

2) Go into map view

3) Launch the rocket

4) Activate trajectories

5) Lock up your game with NaN errors

I removed trajectories and was unable to reproduce this lock-up. However if you're at all still interested in tackling this problem, here is my output_log.

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Dexter9313

Dexter9313

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Hi all. Maybe I don't understand something, but the mod doesn't seem to work in carreer for me even if I upgrade the Tracking Station (I upgraded it only once, but I don't think being able to se asteroids will help). So basically I have patched conics available and nothing is displayed related to the mod, not even the Toolbar's logo. Thanks for your help ! (If you think it's a bug, I'll do whatever I can to help you troubleshoot it, but I'll wait for your opinion on that.) By the way, I use stock model.

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Kobymaru

Kobymaru

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I am getting a NaN lockup when trying to launch a rocket, going in to map view and turning on trajectories.

I removed trajectories and was unable to reproduce this lock-up. However if you're at all still interested in tackling this problem, here is my output_log.

Thanks for the note! I have seen this before and it is definitely a trajectories error, but I couldn't find a reliable way to reproduce it yet. If you're interested in helping out, you could try to find the conditions where the error occurs!

nothing is displayed related to the mod, not even the Toolbar's logo. Thanks for your help ! (If you think it's a bug, I'll do whatever I can to help you troubleshoot it, but I'll wait for your opinion on that.) By the way, I use stock model.

There is some career-disabling logic in place, but TBH at least the Toolbar Logo should be displayed. Could you check that you installed it correctly? Which version do you use? Does it work in Sandbox mode?

- - - Updated - - -

Regarding the accuracy issues, I have good news and bad news. More info in the dev thread.

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Hektos

Hektos

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Thanks for the note! I have seen this before and it is definitely a trajectories error, but I couldn't find a reliable way to reproduce it yet. If you're interested in helping out, you could try to find the conditions where the error occurs!.

I thought the steps in my last post would have been enough :P

Steps to reproduce

1) Make sure you have the newest FAR installed and the newest Trajectories

2) Start a new sandbox game (to rule out Career blocks)

3) Create a rocket that has the following parts (all stock)

4) Go to map view

5) Hit spacebar to launch the rocket

6) Press the trajectories button to activate the mod

7) Lock the game with NaN errors.

Following these steps locks the game up every time (100%) for me.

I hope this is what you meant? I'm down for doing additional test if you want, just be specific at what you are looking for :)

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Kobymaru

Kobymaru

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I removed trajectories and was unable to reproduce this lock-up. However if you're at all still interested in tackling this problem, here is my output_log.

Sorry, I misread that and only saw "unable to reproduce" :confused:

Steps to reproduce

1) Make sure you have the newest FAR installed and the newest Trajectories

2) Start a new sandbox game (to rule out Career blocks)

3) Create a rocket that has the following parts (all stock)

4) Go to map view

5) Hit spacebar to launch the rocket

6) Press the trajectories button to activate the mod

7) Lock the game with NaN errors.

I can reproduce this and will work on a fix.

Also, how can you launch the rocket in map view? Staging is disabled there ;)

Correct order:

3) Create a rocket that has the following parts (all stock)

4) Hit spacebar to launch the rocket

5) Go to map view

6) Press the trajectories button to activate the mod

7) Lock the game with NaN errors.

I'll investigate this. Anyone who wants to help is welcome.

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Dexter9313

Dexter9313

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There is some career-disabling logic in place, but TBH at least the Toolbar Logo should be displayed. Could you check that you installed it correctly? Which version do you use? Does it work in Sandbox mode?

Nevermind, everything works fine ^^ I just didn't notice we now have to right click to pop the menu up. So I left clicked, saw nothing happened aaaand deactivated the trajectories at the same time without knowing so it was normal I didn't see it. As for the Toolbar logo, I think seeing it not working made me think it wasn't even there. Sorry for the useless trouble.

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Superfluous J

Superfluous J

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I'm having a lot of situations (seems mostly on airless worlds, and it may just be Minmus) where the X doesn't show. I see it sometimes but not all the time, implying that it *should* show. I can probably whip up some pics if nobody else is seeing it.

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Kobymaru

Kobymaru

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Posted
I'm having a lot of situations (seems mostly on airless worlds, and it may just be Minmus) where the X doesn't show. I see it sometimes but not all the time, implying that it *should* show. I can probably whip up some pics if nobody else is seeing it.

Yes, it should show. Yes, please do whip up some pics. Bear in mind that on bodies with high rotation rate (such as Gilly or Minmus), the impact point might be on the other side of where the trajectory ends at the moment of prediciton.

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Hektos

Hektos

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Posted
Sorry, I misread that and only saw "unable to reproduce" :confused:

I can reproduce this and will work on a fix.

Also, how can you launch the rocket in map view? Staging is disabled there ;)

Correct order:

3) Create a rocket that has the following parts (all stock)

4) Hit spacebar to launch the rocket

5) Go to map view

6) Press the trajectories button to activate the mod

7) Lock the game with NaN errors.

I'll investigate this. Anyone who wants to help is welcome.

Glad to see I'm not going crazy :P I wish I could I help more, but I have zero knowledge of the code in KSP :/

As for staging in map view, I use Alternate Resource Panel, which has an option to allow staging in map view ;)

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DauntingFlyer

DauntingFlyer

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Posted
I'm having a lot of situations (seems mostly on airless worlds, and it may just be Minmus) where the X doesn't show. I see it sometimes but not all the time, implying that it *should* show. I can probably whip up some pics if nobody else is seeing it.

I do have the same issue, observed in Minmus as well. The X is concealed below hilly regions but shows up again in flatter places. There's an easy work around, just activate "Body-fixed mode". Where the white line ends is where the X should be.

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eightiesboi

eightiesboi

Posted
Posted
Usually, this is an issue of wrong AoA settings. Trajectories can't (or rather won't) guess your flying, so you can set the AoA (or the pitch) in the descent profile. It defaults to 0°, but if you reenter with a single capsule and point retrograde, it should be -180°. Try that first.

Also, which versions of Trajectories and NEAR are you using?

Oh, and also wings dont work yet. If you have wings, your prediction will be wrong.

Thanks! I think that was exactly my problem--I had left everything at 0°, stupidly thinking that default was best and not realizing what the interface was asking me (high courage, but high stupidity--chuck me into a capsule and say goodbye!). Using the latest versions of NEAR and Trajectories (thank you CKAN!).

Thanks for the quick response Kobymaru!

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