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[old thread] Trajectories : atmospheric predictions


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Been having some fun with this. Reverted to stock for the time being.

However, the game begins to chug when the active craft is destroyed (by ploughing it into the ground). Lots of frames dropped until you leave the scene.

I've not investigated this issue yet, but added it on the bug tracker.

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I just released v0.2.1 which now works with NEAR too :-)

Also, it works with the stock aerodynamic model, excepted for wings. I haven't found any data about how KSP simulates wings, and I really don't feel like making tests to find out, so unless someone makes that work, it will probably never be implemented. Anyway, it's very likely that they will change the aerodynamic model at some time, so it's probably not worth spending time trying to guess what they are doing.

Edited by Youen
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Yes, and yes :-)

To do it properly, I would have to implement a new maneuver node system though, because I don't see any way to place the nodes on a trajectory that is not the one computed by KSP. The first part will be to use the nodes that are placed before atmospheric entry, and this part should be straightforward to implement, but I don't know yet what I will do for nodes that are after.

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Yes, and yes :-)

To do it properly, I would have to implement a new maneuver node system though, because I don't see any way to place the nodes on a trajectory that is not the one computed by KSP. The first part will be to use the nodes that are placed before atmospheric entry, and this part should be straightforward to implement, but I don't know yet what I will do for nodes that are after.

i dunno if i understand your answer. I'm talking about I come into the duna system and place a maneuver node to put me on an aerobrake trajectory through the atmosphere, is it possible for that node to show my orbit after the aerobrake but including the change due to the node?

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i dunno if i understand your answer. I'm talking about I come into the duna system and place a maneuver node to put me on an aerobrake trajectory through the atmosphere, is it possible for that node to show my orbit after the aerobrake but including the change due to the node?

Not yet, but that's the aim by the time they're done.

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i dunno if i understand your answer. I'm talking about I come into the duna system and place a maneuver node to put me on an aerobrake trajectory through the atmosphere, is it possible for that node to show my orbit after the aerobrake but including the change due to the node?

Until this is implemented just use the maneuver node to get your orbit just touching the top of the atmo and do the burn, then delete the node and just keep adjusting until you get the desired capture orbit, shouldn't be to hard to do since these kind of adjustments are usually not last minute suicide burns, unless you are using RT2 and have signal delay in which case I guess you will just have to wait until it's implemented or do test runs lol.

I do have a question though:

Are the trajectories drawn across SOI changes? Like if I am adjusting my Jool encounter while still in Kerbols SOI will it draw the Tragectory data for when I encounter Jool? Also will it show SOI changes after the aerobraking, useing the Jool example again, if I'm in Jools SOI on an aerobraking orbit will the trajectory show for instance an encounter with laythe after the aerobrake if I am lucky enough to time such a thing?

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i dunno if i understand your answer. I'm talking about I come into the duna system and place a maneuver node to put me on an aerobrake trajectory through the atmosphere, is it possible for that node to show my orbit after the aerobrake but including the change due to the node?

As Mandelbrot said, not yet.

The thing you want should not be a problem to implement (but not done yet)

In my previous post, I was talking about setting a maneuver node on the trajectory after the aerobrake, for example if you aerobrake arround Jool and want to correct your post-aerobrake orbit to intercept Laythe right after that. This is the part I'm not sure how to do because KSP won't let me put the node on a trajectory that only exists within the mod.

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Until this is implemented just use the maneuver node to get your orbit just touching the top of the atmo and do the burn, then delete the node and just keep adjusting until you get the desired capture orbit, shouldn't be to hard to do since these kind of adjustments are usually not last minute suicide burns, unless you are using RT2 and have signal delay in which case I guess you will just have to wait until it's implemented or do test runs lol.

I do have a question though:

Are the trajectories drawn across SOI changes? Like if I am adjusting my Jool encounter while still in Kerbols SOI will it draw the Tragectory data for when I encounter Jool? Also will it show SOI changes after the aerobraking, useing the Jool example again, if I'm in Jools SOI on an aerobraking orbit will the trajectory show for instance an encounter with laythe after the aerobrake if I am lucky enough to time such a thing?

SOI changes are not implemented yet either. That's the same issue than maneuver nodes : SOI changes before atmospheric encounter should not be a problem to implement, but for SOI changes after arerobrake I'll have to implement the detection algorithm from scratch.

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This mod generally works and is amazing, been looking for something like this for ages!

Have some Rep!

One slight issue, it doesn't seem to be 100% accurate in its predicted landing sites (but damn close and easily good enough!) was wondering if this might be because its factoring in drag from parachutes that haven't been deployed?

Does it take chutes into account? If so when does it assumed the chutes deploy?

I usually don't pop mine until 10km up at the earliest.

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If I'm returning to the surface with my airbrakes deployed, will this plugin account for that, as well?

Yes, but the entire prediction will use the same state. The prediction uses your vessel in its current state, so deploying the airbrakes while you're in orbit should update the trajectory. If the aerodynamic model doesn't update automatically, you can click the "update now" button in the map view. I haven't tested this specific case, so let me know if it doesn't work.

it doesn't seem to be 100% accurate in its predicted landing sites (but damn close and easily good enough!) was wondering if this might be because its factoring in drag from parachutes that haven't been deployed?

Does it take chutes into account? If so when does it assumed the chutes deploy?

I usually don't pop mine until 10km up at the earliest.

I haven't tested it with chutes. The mod uses your vessel in its current state, so I think if the chutes are not deployed (even if you have triggered the corresponding stage), they won't have any effect. Once they semi-deploy, your trajectory will be updated (but that's probably too late to choose your landing site... there's room for improvement here). And same thing when they fully deploy (but then you'll probably land exactly below your current position so you don't need prediction at this stage)

Prediction is not 100% accurate, because of inaccuracies in the simulation (for performance reasons, it takes several shortcuts), and also because it depends on what you do with the vessel during reentry (especially with wings, changing your angle will completely change your landing site, which is the reason for the guides on the nav ball, to help you follow the planned trajectory).

Suggestion: Add the current VERSION and the last update date to the thread title. That's how most mods do it, and it's much easier to keep track of mods that way.

Good idea.

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Loving this mod. Been using it under stock conditions for a while. Seems to give pretty accurate results, although I have had a few (non-winged) crafts where the impact site drifted and needed continual adjustment in the upper atmosphere. Again, I haven't got enough replication steps to detail further. I would say that updated versions seem to have affected (resolved) the frame rate issues I was initially having.

Any chance of hosting this on kerbalstuff? Users are notified when the mod updates and the site has an API for synching GitHub releases.

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Loving this mod. Been using it under stock conditions for a while. Seems to give pretty accurate results, although I have had a few (non-winged) crafts where the impact site drifted and needed continual adjustment in the upper atmosphere. Again, I haven't got enough replication steps to detail further. I would say that updated versions seem to have affected (resolved) the frame rate issues I was initially having.

Any chance of hosting this on kerbalstuff? Users are notified when the mod updates and the site has an API for synching GitHub releases.

Yes, I intend to put it on KerbalStuff, but I wanted to wait for it to be stable enough. Actually, I didn't think about the notification system that is even more useful for players that are waiting for bugfixes... So I'll probably put it there soon, though I don't have the time right now.

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Congrats on being featured on Modding Monday this early :)

On the topic of re-implementing SOI transition detection and maneuver nodes: Don't. It would be much, much easier, and much more compatible to other mods to hack the current rails system to do what you want (e.g. by making the current patch end when leaving the atmosphere, and appending a new (stock) patch with the position, time and shape that was predicted by your plugin.

This will probably involve some really ugly hacking, such as forcefully replacing the trajectories every engine tick, but it will still be better than re-implementing core mechanics of the game...

Wolfwood: Interesting idea... that will be a lot more complicated though, seeing how the vessel's aerodynamic model and TWR changes during ascent... the user would need to specify a throttle and AoA curve, and the plugin would need to perform calculations similar to those done by KER.

Edited by mic_e
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I'm kinda confused still on how to use this. I had hoped this would let me target something near the KSC and then give me guidance on where to burn for deorbit but I'm guessing that's more then it can do. EDIT: I'm on the x64 version.

Edited by Bigred2989
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