How to nicely exit Kerbin's SOI

[Cochonrambo31]

I had a lot of interplanetary missions in my 1200 hours spent on this game.

Not a single one worked.

What's the best way to exit Kerbin's SOI (it can save me a lot of fuel) I tried to burn straight up, it doesn't work cause my Kerbol orbit in too excentric.

[Skorpychan]

Just burn prograde until your orbital path goes out of kerbin's SoI.

Seems to me like you need to watch some tutorials until you understand how orbital mechanics work.

[Cochonrambo31]

I know how it's working, i can launch a lander from minmus and dock with it's orbital module withouth even opening the map. I'm just asking how to exit Kerbin's SOI without ending up with a excentric orbit, to have a nice orbit without having to do correction burns

[EdFred]

I know how it's working, i can launch a lander from minmus and dock with it's orbital module withouth even opening the map. I'm just asking how to exit Kerbin's SOI without ending up with a excentric orbit, to have a nice orbit without having to do correction burns

To go where? To just barely leave the SOI? If you barely leave the SOI you will be near 0 on eccentricity. However, anytime you are going to any other planet you have to have an eccentric orbit - there is no other way around it. Unless you want to change the PE/AP by 1%, then orbit 1/2, then circularize, then change by 1%, then circularize, then orbit 1/2... but even then you won't be at e=0

Edited July 8, 2014 by EdFred

[Tex_NL]

I do not want to turn this into yet another Pro-MechJeb/Anti-MechJeb discussion but in your case I'd suggest you give MechJeb a try. Not necessarily to have it do the work for you but just to show you how it should be done, MechJeb can be a great teacher when it comes to orbital manoeuvres.

[Motokid600]

What is your destination? And for one thing perform your ejection burns from LKO. Not straight up off the pad. Get to orbit first. Superior planets require you burn on Kerbin's night side. Inferior planets require a burn on the day side. In a nutshell.

[mrabinovich]

I personally found this Scott Manley's videos pretty instructive:

- video about interplanetary transfers.

- general orbital mechanics.

[Cochonrambo31]

I tried MechJeb, it's a really powerful tool for KSP. I'm asking this cause i tried to land on Duna , but i ran out of fuel during reentry, i tried to go too fast and instead of aerobraking i burnt prograde. I'm trying to reach Jool, and maybe to send a probe into it's orbit.

[pincushionman]

It's just like any other transfer orbit - you burn prograde to increase your apokerb until you get a "kerbin escape." When you burn is a function of where you're going - going to Duna, Dres, Jool, or Eloo you burn on the night side of Kerbin because then you're burning in the same direction as Kerbin is moving, thus adding to your energy with respect to your orbit around Kerbol. Burning on the day side is retrograde to your initial (wrt Kerbol) orbit, so you reduce your energy and travel inwards.

Remember that your burn will change your per/apoapsis with respect to Kerbol (Sun), and the most pronounced effect will be 180 degrees from where you are now. So your most fuel-efficient transfer will intersect your target's orbit halfway around the sun, so set up your transfer so that happens when your target gets there.

[EdFred]

I think that if you have 1200 hours in the game and none of your missions ave worked you aren't doing them like you are supposed to. You never point straight at another planet to go there. Just like throwing a ball, you never throw it straight at the target. Everything has an arc (orbit) to it. Every planetary transfer should be eccentric - especially if you are running out of fuel.

Post some screen shots of your trajectories and burn nodes to reach other planets.

[Cochonrambo31]

i just want an orbit with an excentricity almost equals to 0. it's to save fuel, i don't have rockets with high deltav so i don't want to spend a lot of fuel at maneuvers. I know how to reach other planets, with infinite fuel i can do it. My goal is to launch a space probe to Jool. An orbit with excentricity=0 is useless in that case. it's just another question. i thought that doing the escape burn on Normal+ or Antinormal would send me away from this rock that Kerbin is, but i can'g play right now (i'm supposed to be sleeping). Maybe launching a rocket with an inclination of -6° then at Kerbin's AN/DN burn Normal+ so i escape Kerbin and match plane with another planet... like Eeloo The only problem is fuel.

[Yasmy]

Normal = bad (points north if you are going east around Kerbin)

Radial = bad (points away from Kerbin if you are going east around Kerbin)

Prograde = good (points east if you are going east around Kerbin)

Don't burn normal or radial. It is a huge waste of fuel.

Drop a maneuver node, and pull the prograde marker until you have an escape trajectory. (About 1000 m/s.)

Then drag the maneuver node around Kerbin until the escape is parallel with Kerbin's trajectory.

You want a hyperbolic Kerbin orbit which takes you to a low eccentricity elliptical Kerbol orbit.

(You can make normal direction adjustments to your maneuver node after you create the approximately correct 1000+ m/s prograde burn, to help match inclination with your destination.)

Edited July 9, 2014 by Yasmy

[pincushionman]

Oh, you just want to get to interplanetary space? I just did that very thing myself - and I did it the opposite of what I just told you, since I only wanted a small change in orbit around the sun.

From a nearly circular LKO, I waited until "midnight," then burned until I barely got an escape - which was on the opposite side of Kerbin (the side near Kerbol). Since I was going nearly exactly retrograde to Kerbin when I exited the SOI, my entire orbit is now inside Kerbin's, and my eccentricity is just over 0.09.

I plan on riding that around (since I'm closer than Kerbin, I'll actually go around "faster" than Kerbin despite my lower velocity) and messing with the orbit so I can match Kerbin's orbit 60 degrees ahead of the planet, and pretend I sent a probe to the L4 point. As long as I can match orbits well enough it'll look like it despite no real 3-body dynamics.

I'm not sure such a technique would work that well in the real world, though, with that whole n-body thing going on.

[Eric S]

i just want an orbit with an excentricity almost equals to 0. it's to save fuel, i don't have rockets with high deltav so i don't want to spend a lot of fuel at maneuvers.

I think you're missing something people are trying to explain to you. If you care about efficiency, you do NOT want to leave Kerbin's SoI and go into a low-eccentricity solar orbit. You want to time your transfer burn so that you go directly from low kerbin orbit to an orbit that intersects the target planet's orbit, timed so that the planet gets there at the same time your craft does. Yes, this takes some planning, and often some patience.

If you're going to Duna, for example, you can get there with a lot less delta-V if you burn so that you leave Kerbin moving in the same direction that Kerbin is moving, placing your periapsis at the height of Kerbin's orbit, and do it fast enough that the apoapsis is around where Duna's orbit is. Basically, just about any craft that can go from KSC to a Mun landing and return has enough delta-v to orbit Duna and return.

[Cerberus738]

I think you need a bigger rocket to go to Jool. Or a better engine. 1 Nuke engine and a X200-16 fuel tank was enough to get my (very small)probes to Jool and see all the moons. I didn't try to come back with it so i don't know if it could do a return trip. The probes were fired into interstellar space by the launch vehicle and from there they started using their own engines.

Having your eccentricity at 0 (or close to?) when you meet Jool? I think that would take a heck of a lot more fuel to do than an aerobrake around Jool. You can also change the depth your hit the atmosphere fairly easily from when you enter Jool's SOI. so do a quicksave there and try a couple of different depths until one captures you into orbit.

To have your eccentricity 0 you would have to build your orbit on one side. The build it up on the other side. Twice as much fuel. If you just build up one side of your orbit you can still attain a capture with good timing.

[EdFred]

i just want an orbit with an excentricity almost equals to 0. it's to save fuel, i don't have rockets with high deltav so i don't want to spend a lot of fuel at maneuvers. I know how to reach other planets, with infinite fuel i can do it. My goal is to launch a space probe to Jool. An orbit with excentricity=0 is useless in that case. it's just another question. i thought that doing the escape burn on Normal+ or Antinormal would send me away from this rock that Kerbin is, but i can'g play right now (i'm supposed to be sleeping). Maybe launching a rocket with an inclination of -6° then at Kerbin's AN/DN burn Normal+ so i escape Kerbin and match plane with another planet... like Eeloo The only problem is fuel.

Based on this, the problem is not fuel - unless you are building ridiculously small rockets. About the minimum you need (with no gravity assists) to launch to orbit, travel to Jool, and return is around 10,000dV. If you just want to go there, around 6500dV.

Edited July 9, 2014 by EdFred

[Cochonrambo31]

so my 9500m/s rocket can do the job?

...

I've never thought it would be that simple

[Streetwind]

Yes, it's that simple if you leave at the correct time. The thing with interplanetary travel is that the exact fuel cost depends strongly on the alignment of the planets at the time of your ejection burn.

Flying to another planet is essentially a really big, really time consuming rendezvous maneuver - it's the same as flying from Mun to Minmus (or vice versa). If you played this long, you're of course aware that smaller orbits go faster and larger orbits go slower. Therefore, the inner planets orbit the sun faster than Kerbin, and the outer planets orbit slower. This in turn means that at the time of launch, an inner planet you want to go to needs to be behind Kerbin, and an outer planet you want to go to needs to be ahead of Kerbin. As you can see here, if you want to go to Jool, you should launch roughly when Jool is just over "three hours", or a quarter way around the sun, ahead of Kerbin. This will allow you to perform a nice, cheap Homann transfer with no need to overshoot Jool's orbit.

After you have reached such a favorable alignment of planets, launch your rocket into a nice equatorial Kerbin orbit. The more equatorial, the better. Then, create a maneuver node, use only prograde dV, and drag the node around. Do this until your projected orbit when viewed from top down just touches the orbit of Jool, and your exit vector from Kerbin is pointing straight ahead in Kerbin's direction of travel (if you were going towards the inner planets, it would be pointing straight backwards). You may potentially get an encounter (or at least, close approach markers) at this point already, but this isn't always the case, especially when there are inclination differences between Kerbin's orbit and that of the target. If you don't get anything, don't despair; you are still incredibly close, the alignment of planets guarantees it. Also remember to select Jool as your target so you can actually see the close approach markers.

There's two ways you can adjust your inclination. One is a midcourse correction maneuver, using a second maneuver node. It can be very useful when your target orbit differs strongly in inclination and eccentricity (Moho, Eeloo). However, Jool's orbit is nice and well behaved, so you can easily fly a ballistic trajectory (all in one burn) instead. Because you are already spending thousands of dV prograde in your first maneuver node, you can get a certain amount of normal/antinormal adjustment essentially "for free" (especially since you're getting a lot of Oberth effect from Kerbin). Just try and play with the purple markers; you'll notice that you chan lift/lower your orbit a lot with nearly no change in dV cost. Do this until you get an encounter. If the alignment is right, it should only take a few nudges in the right direction before (at minimum) the close approach markers show up.

Once you have your encounter (any encounter), click on the Jool periapsis marker to make the number readout sticky. Now play gently with all six markers (radial in/out is fine to use at this point) in order to get your periapsis as low as possible. Anyting below 20,000km is good, 2,000km is excellent, 200km is perfect (it's almost touching the atmosphere at that point). Also, you may want to focus Jool at this point and make sure that your projected flyby is equatorial and counterclockwise (running behind the planet). If you later brake into orbit that way, you'll have an easy time visiting the moons. You can still access your maneuver node while you have Jool focused, with a bit of clicking.

Then all you need to do is perform the burn... and afterwards check how much of an adjustment you need to make, because even minor imprecisions in the burn can cause large periapsis deviations or even make you miss the encounter.

EDIT: Oh, and don't timewarp through SoI changes. You'll get floating point rounding errors that throw your periapsis off.

Edited July 9, 2014 by Streetwind

[Sinistah]

This should answer your questions about interplanetary travel

http://forum.kerbalspaceprogram.com/threads/27236-Tutorial-Step-by-step-Interplanetary-Hohmann-transfer-guide-and-tips

[Cochonrambo31]

I made it, i tried the LV-N + X200-16, and using my rocket i reached Mun (using it as a slingshot) then Duna. But after setting up the maneuver node to Jool, i stopped playing. 15mins burn are boring.

[Epthelyn]

I made it, i tried the LV-N + X200-16, and using my rocket i reached Mun (using it as a slingshot) then Duna. But after setting up the maneuver node to Jool, i stopped playing. 15mins burn are boring.

Provided your rocket is going to stay burning in the direction you told it to, just leave it for 15 minutes and do something else. Efficiency comes at the cost of longer burn times, unfortunately.