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[old thread] Trajectories : atmospheric predictions


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Regarding the suggestion: I've already implemented it; pull request is incoming :)

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Edit: I've sent the pull request.

Edit: I've sent another pull request, fixing a minor issue. The pull requests should be independently mergeable.

Edit: I have entered some bugs into the issue tracker.

Edited by mic_e
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wow, this is indeed amazing! Not only have you solved the FAR problem everyone said was impossible, but implemented an insanely useful feature!

I'll throw my request hat in with RasterProp support myself, but the node support and stock toolbar integration would be cool too.

In any case, I will be following the github. I may find time yet to contribute to a mod xD.

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This is fantastic! I've always said that there are models for atmospheric reentry trajectories, but now it is lain bare for all to see! My question for the OP: Is there any interest in extrapolating this mod to unfocused vessels/debris? It would be sp awesome to see this get used for a true to life, honest to goodness stage recovery mod which uses the actual physics rather than (admittedly very adequate) number checking.

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Great Idea..

Does it show your landing spot only in the flight scene? Or only on the map. Because if you could show the touch down site with some kind of decal in the flight scenethat would be totally awesome.

The problem with map view only is that it only works on relative large scales. So when you're 'hopping' your colony buildings a few meters map view really is no help at all.

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What am I missing here. I've installed it, but I never see the red lines like others are showing in screenshots. I managed to get a white line to show up if I turned off auto-update, but I never get the red line or an X anywhere...

Not sure what I'm doing wrong?

Do you use FAR ? If yes, do you know what version is installed ? Do you get a white message on the right of the screen when starting or resuming a flight ?

Also, did you download the last version (i.e. Trajectories.zip, version 0.1.1) ?

If you don't use FAR, the mod should use the stock aerodynamic model instead, but apparently this is broken in the current release. That will be fixed in the next release.

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Great Idea..

Does it show your landing spot only in the flight scene? Or only on the map. Because if you could show the touch down site with some kind of decal in the flight scenethat would be totally awesome.

The problem with map view only is that it only works on relative large scales. So when you're 'hopping' your colony buildings a few meters map view really is no help at all.

Only on the map. I'm not fan of displaying stuff directly in the flight scene as it doesn't really fit with the rest of the game (admittedly, an external camera is already a bad thing for immersion, but drawing 3D lines is worst). About precision for setting the target point, I'm planning to add an option to specify an existing object (a flag, another vessel, etc.). And in the flight scene, you have two indicators on the nav ball that tell you if you're on the correct trajectory or not (look at the screenshots in the first post). They'll be embellished in a future release :-)

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This is fantastic! I've always said that there are models for atmospheric reentry trajectories, but now it is lain bare for all to see! My question for the OP: Is there any interest in extrapolating this mod to unfocused vessels/debris? It would be sp awesome to see this get used for a true to life, honest to goodness stage recovery mod which uses the actual physics rather than (admittedly very adequate) number checking.

I don't know how recovery mods work. In fact I don't exactly know how KSP handles objects that reenter atmosphere but are far away (they are just destroyed ?) or crash on a body. The Trajectories mod could help pre-compute a trajectory, or offer an unified interface to compute aerodynamic forces whatever mods are installed (FAR, NEAR, etc.), but at this time it is really targeted at giving you a possible entry trajectory, not computing a free fall trajectory. It assumes you'll keep your wings horizontal and follow the planned descent profile. At no time does it compute torques, which would make debris rotate, which would change drag. Also, I use an aerodynamic force cache that is specific for one vessel. Even if it doesn't use too much memory, having a cache for each debris, assuming there are a lot of them, could become expensive.

To sum up, there are certainly ideas that could be re-used, but it's not really adequate for a recovery mod in its current state.

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On-rails vessels get destroyed once they are below a specific altitude (30ish kilometers), defined by a pressure limit (0.01 atmospheres, I think).

Recovery mods hook into that destruction event, and calculate the vessel's mass/parachute area to determine whether the vessel will survive.

Basically what you/a recovery mod author could do (probably in collaboration) is to run one single simulation when a piece of debris is put on-rails, and store the resulting landing spot/peak g-force. The recovery mod would still have to do its own parachute/mass ratio calculation, but in addition, destruction of debris that enters too steeply would work now.

One step further, it would be possible to use atmospheric simulations for all on-rails craft, once per orbit, to allow things such as letting the orbit decay slowly. That would work _even_ if the craft is actually above the cutoff altitude. Imagine the awesomeness... Watching a 90-km orbit decay over the course of a few weeks...

So while a unified interface to provide aerodynamic forces would be great, a unified interface to provide full simulations of atmospheric patches, yielding things like max-g, resulting orbit/landing spot, and duration, would be much more useful, IMO.

Edited by mic_e
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We'll, is me don't having time to play and the good things start to show up.

Seams amazing this. I'll need to read all post first, but it is like what i already have on MechJeb, but different. Need to try.

I see it check the survival for FAR, rsrsrsrs. Cool

Great Work

Edited by Climberfx
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I don't know how recovery mods work. In fact I don't exactly know how KSP handles objects that reenter atmosphere but are far away (they are just destroyed ?) or crash on a body. The Trajectories mod could help pre-compute a trajectory, or offer an unified interface to compute aerodynamic forces whatever mods are installed (FAR, NEAR, etc.), but at this time it is really targeted at giving you a possible entry trajectory, not computing a free fall trajectory. It assumes you'll keep your wings horizontal and follow the planned descent profile. At no time does it compute torques, which would make debris rotate, which would change drag. Also, I use an aerodynamic force cache that is specific for one vessel. Even if it doesn't use too much memory, having a cache for each debris, assuming there are a lot of them, could become expensive.

To sum up, there are certainly ideas that could be re-used, but it's not really adequate for a recovery mod in its current state.

Oh I'm sure there are obstacles that need to be overcome. The drag profile would be the most difficult one I think. It's easy in stock because drag depends on mass only, so the orientation does not matter (yuck). As for FAR or other models with a realistic drag profile, one could just store the last known orientation of the vessel and assume it never changes. This isn't too far-fetched since KSP already does this when you enter time warp.

After this point, I guess a hybrid system where you check the total heat tolerance / number of parachutes / terminal velocity like DebRefund does to return a yes/no on wether the craft survives. Your mod tells it where on the surface of kerbin it ends up and instead of the game automatically recovering the spent stages, it teleports them to that spot on the map where the player can continue playing or recover manually. No external windows required to manage recovered assets, and it could work on other worlds too - probes to Laythe and Eve could practically land themselves!

Of course for this mod as it is now, I'm very impressed. Just saying how I would do the stage recovery thing. Keep doing what you're doing though. I'm just a fan boy tossing out random ideas. Lol

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I've released a new version. It should now work correctly with FAR and the stock model (auto-selected, you have nothing to do). Let me know if you still have issues such as the red trajectory not displaying, big performance issues, etc.

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Yes, unless you modify the descent profile (you can set your angle of attack or horizon angle for entry, high altitude, low altitude, and near the ground). These angles are used to predict the trajectory, and indicated on your nav ball along with another indicator telling you the direction to go to correct your trajectory in case you've drifted from the target.

For the particular case of aerobraking (without reaching the ground), you don't have indicators on the nav ball, so the simplest is probably to follow the prograde vector (set AoA to 0° for all altitudes). This is something I should improve (for example, allow to target a precise post-aerobrake apoapsis and use the indicator for that)

Edited by Youen
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I agree, 3d lines would be ugly... But, an optional "x marks the spot" where your plot intersects the ground might not be so bad?

It would do wonders for peoples ability to do precision burns over small distances.

Hint hint poke poke :P Hehe, it's your mod, your vision, I think it's already tremendously usefull so I'll be using it either way.

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Oh I'm sure there are obstacles that need to be overcome. The drag profile would be the most difficult one I think. It's easy in stock because drag depends on mass only, so the orientation does not matter (yuck). As for FAR or other models with a realistic drag profile, one could just store the last known orientation of the vessel and assume it never changes. This isn't too far-fetched since KSP already does this when you enter time warp.

Proper FAR prediction always has been a major headache and probably will remain so. Aerodynamics are a rather complex affair and FAR manages to replicate that with a decent amount of accuracy.

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Possible bug report: a second (non-focused) craft which is throttling leads to flickering GUIs when it leaves the physics range of the focused craft.

This was using FAR, many other mods. Need to replicate.

That MAY be an issue with FAR itself. I have had the same issue and have never used this mod. Maybe take a look over at the FAR thread?

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