How do you force interplanetary encounter nodes together?

[Wizard Kerbal]

     All right, 170 days to Gilly, the current date is Year 2,  Day 293. Now just to go back. Wonder how long that will take. Hey i'm at a transfer window- wait. No, Kerbin is 54 degrees behind me.

      30 minutes of fiddling with maneuver nodes later, i'm here. My closest encounter is still about 11,400,000 kilometres away, with me already passed it's location. How would one force encounters together in a reasonable time? I got angry and pressed skip orbit a lot, and It would be 1 year, 40 days before it would be easy to force the nodes together, and I don't want to do that to be honest.

Edited March 23, 2021 by Wizard Kerbal
I have 2 nuclear stages, I plan to ditch my auxiliary tanks in Eve's atmosphere then have 2,000 m/s to get an encounter.

[king of nowhere]

i'm not sure what you are asking. i think you are asking about doing interplanetary transfer outside of a transfer window? would fit with the window being a bit more than one year later.

well, short answer is, you don't. i mean, you can, but it costs an inordinate amount of deltaV and/or time. unless you have a long ion stage, you will need manuevers that will make you lose time.

if you still want to try...

ok, two ways. first is intercept in multiple orbits, and second is force a direct intercept with large cost. Unfortunately i am using mobile connection and can't show you pictures.

so, first way. you just intercept the orbit somewhere. you want to go back to kerbin? well, kerbin orbits at 13.5 Gm from kerbol, so you make an orbit with an apoapsis there, and 0 inclination. you will reach your apoapsis when kerbol will be somewhere else, but it's ok... orbit after orbit, sooner or later you will meet kerbin. eventually. Not a great idea. You can help this encounter by burning at apoapsis: lower periapsis for a faster orbit, raise it for slower orbit, this way you can syncronize your time for a future encounter. in any case, it will take multiple orbits, and it will be slightly more expensive than a direct transfer, but there are reasons to use that; most common when you are doing gravity assists, so you don't have the luxury of having planets aligned.

Second way, force a fast intercept. Ok, so again the thing to know is that if you raise your apoapsis, the orbit will be slower. so, kerbin is behind you and you will miss it? but for a high solar apoapsis, you will slow down, and you can meet kerbin on the way back. this manuever is VERY expensive; expect a kerbin intercept speed of many km/s.

There is even a third way, a variation of this, when you want to really spend a ridiculous amount of deltaV: point your navball to the target, and burn like there's no tomorrow. eventually you'll go so fast, kerbol's gravity will be negligible. it doesn't have many practical applications.

[Wizard Kerbal]

1 hour ago, king of nowhere said:

There is even a third way, a variation of this, when you want to really spend a ridiculous amount of deltaV: point your navball to the target, and burn like there's no tomorrow. eventually you'll go so fast, kerbol's gravity will be negligible. it doesn't have many practical applications.

Realizing what you meant, I said, "Dear god" out loud.

 

1 hour ago, king of nowhere said:

Second way, force a fast intercept. Ok, so again the thing to know is that if you raise your apoapsis, the orbit will be slower. so, kerbin is behind you and you will miss it? but for a high solar apoapsis, you will slow down, and you can meet kerbin on the way back. this manuever is VERY expensive; expect a kerbin intercept speed of many km/s.

Yeah, I don't know why I didn't think of that. It will be a fast re-entry, but I have a heat shield with 50% ablator. But wait, heat shields do melt before all of their ablator is gone. 

Edited March 22, 2021 by Wizard Kerbal
Y'know? I think the reason I didn't think of that is because I once saw a very angry sign saying, Your return course can't go lower than kerbin(from jool,) It has to be as low as kerbin's height!

[maddog59]

8 minutes ago, Wizard Kerbal said:

Realizing what you meant, I said, "Dear god" out loud.

LOL - no kidding!

"If G-d hadn't given us the infinite fuel cheat, it would've been necessary for Squad to have invented it" (my apologies to Voltaire).   

[king of nowhere]

now that i have again a decent connection, i can post some pictures. link to some old pictures from my mission reports, actually, but i couldn't see them when i had a slow connection that failed to load

So, examples of type 1

here i was going from eve to kerbin. i was in an elliptic eve orbit and i had little fuel, so i could not choose the direction of ejection - and it was wrong for a normal transfer. so i placed the orbit in a way to intersect kerbin, eventually. my orbital time was very close to that of kerbin, so it took 8 years.

 

Here I am going back from jool, i just had to return to finish a challenge and i didn't want to deal with transfer windows, so i made the first burn in jool's orbit to put solar periapsis on kerbin's level. once i was at periapsis, a retrograde burn changed my orbital period until i had an intercept the next time i would be there. it still took longer than it would have to make a regular transfer, but it was the lazy approach: i burned out of jool's system until my periapsis was 13.5 Gm, then i time warped to periapsis and i burned retrograde until i got an encounter. didn't require any fiddling with manuever nodes

 

Here I return from a gravity assist. I wanted to reach Duna after a kerbin flyby, but the two planets were in the wrong positions. So I spend one or two orbits in a parking orbit (purple) before raising apoapsis for a Duna capture. this is a slightly modified version, i had to pick the right periapsis to get the timing right. Again, it was part of a long sequence of manuevers.

 

Here instead I will show some fast trajectories. They are from my kerbalism grand tour, having life support forces one to take some design choices. I'd never have particular reasons for using those trajectories in the stock game otherwise. Here I designed an ion powered escape pod/return vehicle with 15 km/s deltaV because life support and kerbal healtcare would be issues requiring urgency

This is an Eeloo return in less than one year. It costed 7 km/s. I burned mostly radially to achieve it, with just some slight corrections based on where kerbin would be. since the trajectory brushes past kerbin's orbit, the intercept speed is actually quite sane given the circumstances: roughly 3 km/s, bringing the total deltaV for the trip at 10 km/s. To find this trajectory I burned retrograde to lower periapsis, and radial to reduce time to periapsis, until i was crossing kerbin's orbit at periapsis in more or less the desired time. then i adjusted inclination until i could find a close approach. then i refined the close approach.

 

Here I am returning from Dres. Kerbin is in the totally wrong position to return in less than one year, so to catch it i'd have to take a very close slingshot near the sun to be faster. 7.5 km/s ejection from Dres, 10 km/s Kerbin intercept. But return from Dres in 230 days outside of a transfer window; a normal travel time is a couple years. To find this trajectory I burned radially and retrograde to make a close slingshot past the sun, and i adjusted the inclination to find a close approach marker. if i was behind the planet, i needed to go faster, so i added more retrograde and radial. repeat until approach.

 

Finally, this is a slightly more sane version of the previous trajectory. it gives up on intercepting Kerbin on the other side of the sun, and it just crosses its orbit when it is passing in a convenient point. It only costed 3 km/s to get the intercept, but because I'm crossing kerbin's orbit at almost a right angle, intercept speed is 11 km/s. the dolphin capsule can survive reentry at 9 km/s, i had to slow it down a bit. I covered the minmus-kerbin distance in less than one hour. To find this trajectory, i burned retrograde until i was reaching kerbin's orbit in less than one year. then i roughly eyeballed where kerbin would be by that time, and i used prograde/retrograde to adjust my position to get more or less close to there. fixing inclination got me a close approach marker, then i just had to refine.

 

so, i hope that helps in case you have to find trajectories outside of regular transfer windows. but it is unlikely to appease to your current situation, as a type 1 trajectory will lose you more time than just waiting the transfer window, and a type 2/3 trajectory... well, i somehow doubt you packed so much deltaV unless you were planning in advance to do something like this

 

 

 

 

Edited March 22, 2021 by king of nowhere

[Guest]

Mechjeb’s pork chop planner is useful for this. Basically you get a coloured ‘heat’ graph which compares dV, time to burn and transit time into a single selection option. As king of nowhere says you can usually trade time for dV and vice versa. Personally, I refuse to wait for planets to align perfectly so I use it a lot.

[Wizard Kerbal]

1 hour ago, FruitGoose said:

Mechjeb’s pork chop planner is useful for this.

That sounds good if I wasn’t on console...

[Guest]

15 minutes ago, Wizard Kerbal said:

That sounds good if I wasn’t on console...

Haha well yes that does pose a slight problem with my suggestion to be fair!

[Snark]

(never mind-- was going to suggest "could you please post a screenshot" but then I saw a later post where you said you're on console)

[The Aziz]

6 hours ago, Snark said:

(never mind-- was going to suggest "could you please post a screenshot" but then I saw a later post where you said you're on console)

Which is entirely possible but with few extra steps because consoles don't like sharing outside their ecosystems. Regardless..

Console or not, you can still use a 3rd party tool on the internet. https://alexmoon.github.io/ksp/ pick bodies, current time and look at what it gives you. Fiddle with the results to find the one that fits you the most and go for it.

[Empiro]

If your closest approach is 11 million km, then you're not anywhere close to Kerbin. The distance of Kerbin to the sun is 13 million km. Without expending an enormous amount of delta-V, the only way to get an encounter will be to wait.

You might be able to get an encounter a little bit earlier by putting a maneuver node at the intersection of your orbit and Kerbin's. You won't make the encounter the first time you get there, but if you put a maneuver node there, you may be able to get an encounter the next orbit or the orbit after that with a modest amount of delta-V in the prograde or retrograde direction.