Online Calculator for Trajectories with Multiple Gravity Assists

[Krafpy]

Hello and thank you for your message @Utkucan !

If you want to have some details on what the tool does internally you can see one of my previous posts :

Note that this post describes how the tool worked when I released it. It has some mistakes and the current version has some differences. But this should give you a rough idea at least about "how it calculates an optimal trajectory" (keep in mind also that there is no guarantee that the result is the optimal trajectory).

If you want the exact details on how it works now or have specific questions, don't hesitate to ask or even direct message me.

 

On 3/22/2023 at 2:39 PM, Utkucan said:

What are the parameters and options that you can adjust? How do you interpret the results and export them to the game?

I'm not sure if you are talking about the parameters you can change in the user interface (e.g. departure planet, departure date... etc.) or internal parameters in the optimization algorithm.
For your second question : I'm not sure about what you mean by "interpret and export them to the game". The tool gives the information of each maneuvers you have to perform and when. You basically have to try to reproduce them in game. However, due to precision and simplification issues, following the steps in game exactly is unlikely to give you the exact same trajectory that the tool shows you. So manual fine tuning is required.

On 3/22/2023 at 2:39 PM, Utkucan said:

I would also like to ask you if you could create a tutorial video for beginners on how to use the ksp mga planner. I think this would be very helpful for people who are new to this tool or to multiple gravity assist maneuvers in general. A tutorial could show some examples of how to plan different types of missions, such as interplanetary transfers, flybys, or rendezvous.

This is something someone else already asked in a comment a few weeks ago ( @akyyy). I'm a bit busy and, mainly, don't have a PC that can run KSP decently right now. I'll try to make one as soon as I get the time for it.

I hope this helps ! Don't hesitate if you have further questions.

Edited March 23, 2023 by Krafpy
Fixed typos

[Eddy119]

Hi, 

@theAstrogoth's tool works well for low Moho orbital insertion from low Kerbin orbit via 2 Eve gravity assists, with an average of 3200m/s for each year. I have calculated every year up to year 21 for a Kerbin-Eve-Eve-Moho route. 

This can be done by inputting 71000 for Kerbin orbit, 10000 for Moho orbit, adding 1 Deep Space Maneuver for the Eve-Eve leg, and unchecking the no insertion burn box at mission settings. 

Basically, you do an Eve transfer for ~1500m/s a bit later than when you're supposed to when doing a normal Eve transfer. You want to meet Eve when it is at the ascending/descending node of Moho orbit (which coincidentally happens to be Moho's aphelion/perihelion) so you can tilt your orbit to match Moho's inclination. You want to also meet Eve at the same place 1 Eve orbit/year later. Then the next time you meet Eve you reduce your perihelion to meet Moho near its perihelion. 

Year 2 Day 222 2707m/s

Year 13 Day 192 2597m/s

All of each year's windows up till year 21: https://docs.google.com/document/d/1gQ5Rqj28xz9VmWYp02KwDkiTwwKr8COoaGOh8hgsh7M/edit?usp=sharing

Combined with self-gravity assists of Moho, (aka vinf leveraging maneuver) by intersecting Moho's orbit at its tangent (perihelion) bending radial in/out for your orbit to intersect Moho's orbit and at aphelion of your orbit burning prograde to meet Moho's orbit at its tangent (perihelion) after a few Moho orbits again, you can save even more fuel. This is what MESSENGER did and BepiColombo is doing now. Here is the source of that: https://forum.kerbalspaceprogram.com/index.php?/topic/208730-messenger-style-mission-to-moho/#comment-4150697

I want to make something like this for KEKKJ Kerbin-Eve-K-K-Jool but I can't make it work.

I also added a graph of the delta v required (not including Moho self assists) for each year and 3 windows that only require 1 eve assist on year 7 day 175 year 10 day 202 year 18 day 197 etc... that only takes 3000m/s (2600m/s for year 18) in the Google Doc. 

Edit: Average mission duration of Ke-Ev-Ev-Mo is 1 year 200 days

Edit 2: Oh, and also you probably even more (a lot of? idk) delta v if you burn to an inclined orbit instead of equatorial. A significant amount of the departure burn involves radial burn.

Edited April 15, 2023 by Eddy119

[Eddy119]

If you match the inclination at launch you save even more delta v. Here is Year 2 Day 218 for 2393m/s.

(I just tried to do the year 2 window and I ended up using 3600m/s probably because I screwed up.)

[Krafpy]

Hi ! Thank you for all the information and work you did !

22 hours ago, Eddy119 said:

Oh, and also you probably even more (a lot of? idk) delta v if you burn to an inclined orbit instead of equatorial. A significant amount of the departure burn involves radial burn.

Yes my tool always suppose an equatorial departure orbit, which is pretty bad in terms of dV. I will see if I can make it consider the inclination, or maybe even add the inclination as a part of the optimization process.

22 hours ago, Eddy119 said:

Basically, you do an Eve transfer for ~1500m/s a bit later than when you're supposed to when doing a normal Eve transfer. You want to meet Eve when it is at the ascending/descending node of Moho orbit (which coincidentally happens to be Moho's aphelion/perihelion) so you can tilt your orbit to match Moho's inclination. You want to also meet Eve at the same place 1 Eve orbit/year later. Then the next time you meet Eve you reduce your perihelion to meet Moho near its perihelion. 

I want to point out that I have (almost) no control over what trajectory is produced by my tool. It tries to find a trajectory that minimizes the total dV with what is basically a "smart evolutionary trial and error" algorithm generalized for any planet sequence. So it has no idea that good human-found strategies for specific trajectories exist, and can fall in a local minimum.

[Dartio]

Hello,

I play on KSRSS scale 1/9.  I would like to know if the mod take KSRSS mod into account.

Because the site does not take KSRSS.

Thanks in advance for a feedback.

Dartio

[Krafpy]

Hello @Dartio!

My tool doesn't support KSRSS for now, you can check @theAstrogoth's tool which has a KSRSS option : https://kerbal-transfer-illustrator.netlify.app/Flyby but it seems to be scale 1/10

Do you have by any chance a link to the Kopernicus config files of the 1/9 scale version ?

[Dartio]

Hello @Krafpy

Thank you for reply !

I play with this mod : https://gitlab.com/ksrss/KSRSS/-/tree/reborn/KSRSS

I check @theAstrogoth'tool, but doesn't work with my mod.

[theAstrogoth]

On 4/22/2023 at 12:45 PM, Dartio said:

I check @theAstrogoth'tool, but doesn't work with my mod.

I can try to help you get it to work! Let's chat via PM or in the relevant thread so that we don't clutter up the discussion here.

[akyyy]

I can't do it.

 

Example: Kerbin-Eve-Duna flyby.

I set the departure values, create the manoeuvre. It meets Eve, but not the Duna. I see where the probe would be and the position of the Duna, but no flyby.

[Krafpy]

Hi @akyyy sorry to hear that

Do you mean that if you follow step by step what is indicated by the tool you don't get immediatly the intersections/flybys ? If it's that then it's completely normal. The results (times, maneuvers...) are internally computed with some assumptions and simplifications. It is very unlikely that following the details of the trajectory will give you the exact same one in game. You need to fine tune manually the maneuvers in order to enforce flybys to happen more or less how the tool displays them.

I tested with a Ke-Ev-Mo trajectory and when I entered the Ke-Ev maneuver as indicated it didn't even give me an intersections with Eve although the tool computed that it would. However, after I modified a bit the maneuver by hand (about 50~ m/s dV change and moved it later/earlier) I got the intersection.
Remember that the tool gives more or less precise idea of what the trajectory would be and what maneuvers to do.

I promise I'll do that video tutorial ! sorry for the wait

[Eddy119]

I just made a separate post for this question but I'm wondering if it's possible for someone to find a semi regular list of launch windows for the KEKKJ/KEEKJ/other gravity assist ways to go to Jool under 1200m/s? Can't get the online finders to give me proper trajectories...

[Krafpy]

@Eddy119 I am not aware if such list exists. Maybe try creating it with KSPTOT ? It might be better at finding launch windows (if you are just looking for that). The best I got with my tool is 1500m/s for KEKKJ (without insertion burn).

[akyyy]

On 6/2/2023 at 6:29 PM, Krafpy said:

I promise I'll do that video tutorial ! sorry for the wait

No problem. I'm waiting.  

[Krafpy]

@akyyy The video is recorded, currently editing it.

[Vals_Aerospace]

Out of curiosity, would it be possible to add a system scale modifier? That way people can use this tool if they play on 2.7x or 2.5x KSRSS or Stock system.

 

(I have absolutely no idea if that's actually possible lol)

[RE-I2 Skiff]

So it's possible to load the data of the transfer in an excel file. Is there any way to open said file in the planner for later use?

[hall]

Is there any way to have this tool use moon flybys? Such as Ke-Mu-Ev-Gi-Du, for instance

[Krafpy]

Sorry everyone for the terrible delay in my response !

On 12/25/2023 at 4:38 AM, Vals_Aerospace said:

Out of curiosity, would it be possible to add a system scale modifier? That way people can use this tool if they play on 2.7x or 2.5x KSRSS or Stock system.

 

(I have absolutely no idea if that's actually possible lol)

It would be possible. At least, I don't see anything that could prevent me from implementing it in the current software.

 

On 12/31/2023 at 12:34 AM, RE-I2 Skiff said:

So it's possible to load the data of the transfer in an excel file. Is there any way to open said file in the planner for later use?

There is no way for now. I am well aware this should be a feature... I just didn't design the software initially to support that... but it is something I can try to add. I don't think it would actually be that hard for me to implement it, since the excel file contains all the required data to retrieve the full trajectory.

 

On 2/12/2024 at 4:55 AM, hall said:

Is there any way to have this tool use moon flybys? Such as Ke-Mu-Ev-Gi-Du, for instance

For now, it is not possible, and I currently have no idea how to implement that. It doesn't mean that it won't be implemented in the future though.

 

I'm currently pretty busy with my studies. I hope to get some time soon to finish things I promised almost a year ago now... (didn't forget about you @akyyy !)  Once again, I apologize for the delay!

I began experimenting a bit with a mod version of the software (for KSP1) last year. I put it on hold it during the summer as I failed to fix an issue with orbit calculation (if anyone has some knowledge in mod development and is interested, dm me!). But I believe most of the requested features regarding custom solar systems and game configurations (e.g. system scale) would be implemented much more easily and reliably with a mod version, so I'll probably postpone them for the mod. Though, I'll still try to work on the current web tool if the features don't require too much refactoring of the code base; I'll keep your requests in mind!

I'll try to respond to this thread much more often.