Most Efficient Way to get to Eve?

[blueshirt21]

I know I'm probably doing it wrong, but I for the life of me cannot figure out the most efficient way to get to Eve. I try using the Interactive Illustrated Calculator, but I just end up in a higher orbit. Right now I'm forced to orbit around Kerbol, then waste huge amounts of fuel lowering the orbit to intersect with Eve. Same goes for Duna as well, but that's not as hard.

[Grizzlol]

It should not take much fuel to correct the orbit up and down, except for Moho. The most fuel-efficient way to correct anything is as soon as possible, that is, as far away from the destination as possible. So departing from Kerbin, you should start correcting the moment after you have finished burning for the transfer, at which point you will still be very close to Kerbin and Kerbol's periapsis (assuming that you are doing an interplanetary transfer). If you are having to spend a lot of fuel at this point then your phase angle must be way off to begin with. Perhaps you just need to spend more effort in taking off at as precisely 270 or 90 degrees as possible.

Also, using said calculator, you should be able to make an elliptical transfer trajectory aligned with the destination body's orbit in such a way that you do not have to burn to match the orbits completely, but rather head for a collision course. This requires a lot of accuracy but is not too hard to accomplish from Kerbin to Eve or Duna. Having to orbit around Kerbol is not really a bad thing as there is no time limit, but if you miss the encounter on the first pass-by using that calculator then you will either have to wait for another encounter by chance, or spend a ton of fuel to do a rendezvous instead.

Perhaps you would learn more watching videos. I would recommend Scott Manley's channel on YouTube, for example.

[felixar90]

Higher orbit? Did you miss the part where you are supposed to launch with a 270º heading (180º inc.) when going to inner planets? unlike outer planets, the ejection angle is relative to Kerbin's retrograde.

(You must orbit clockwise around Kerbin. Pack extra power because you'll be going against Kerbin rotational boost.)

[EvilotionCR2]

grrrrrrrrrrrrrrrrr... why everyone love Eve?I do a base here...Nothing interesting here

[Hillstache]

Higher orbit? Did you miss the part where you are supposed to launch with a 270º heading (180º inc.) when going to inner planets? unlike outer planets, the ejection angle is relative to Kerbin's retrograde.

(You must orbit clockwise around Kerbin. Pack extra power because you'll be going against Kerbin rotational boost.)

Good advice, I found the 270 degree launch to Eve worked very well.

[blueshirt21]

All right, will try the 270 turn.

[Kosmo-not]

STOP! Why are people talking about launching into a 270° orbit? That's just silly.

It sounds like you are not doing your ejection burn at the correct angle. Remember that the ejection angle is the angle between where you want your trajectory to take you and the ejection point.

[Grizzlol]

Taking off at 270 degrees will put you in a retro-direction in relation to the orbit around Kerbol, which is not silly at all when you want to go to a lower orbit. In fact, it would just be silly to go 90 degrees.

[Candre]

I don't think it would. With a 90 degree heading, all you have to do is flip olex's ejection angle diagram left-to-right to get the correct ejection parameters. It also has the advantage of a speed boost from Kerbin's rotation.

Edited September 24, 2012 by Candre

[thorfinn]

Taking off at 270 degrees will put you in a retro-direction in relation to the orbit around Kerbol, which is not silly at all when you want to go to a lower orbit. In fact, it would just be silly to go 90 degrees.

Unless you think that any equatorial orbit will have you going pro-grade wrt. Kerbin at one point and retrograde at the opposite side. You just flip the angles.

[blueshirt21]

Okay, okay, I'm not having much luck at all.

270 degree orbit. Check.

The calculator gave me a phase angle of -54.13, so I waited until the MechJeb phase angle thingie said -54.13. Then I waited until I got an ejection angle of 152.99 degres retrograde, which is 27.01 degrees prograde? (Using the mechjeb angle to prograde under orbital information)

The second it reached 27.01, I kicked my engine to full throttle, burning until I got to 3061 m/s-but my orbit was not even close to Eve-with an apogee above Kerbin orbit. I tried burning to correct, but I just ended up nowhere.

I can get to Duna fine. Probably Jool too (havent tried, but seems the same as Duna except way more thrust) but I just cannot get to Moho or Eve for the life of me.

I'll go try watching some more Youtube videos. Or just sulk at my Ike base.

[Hillstache]

I'll go try watching some more Youtube videos.

I have a

where I do just that, have the angle at -54 degrees (though I screwed up and it was actually -50), and burned at the correct ejection angle, I do easily get to Eve's orbit, then I have to mess about to fix my angle issues, and succeed!

[felixar90]

152.99 degree retrograde is 27.01 degree FROM prograde. It would be 332.99 degree to prograde.

I never noticed there was a angle to prograde in Mechjeb. I use a on-screen protractor.

[blueshirt21]

I'm actually watching your video right now. Stross IV? I'm basically going to copy exactly what you do....even the failures.

[blueshirt21]

felixar90-I was never good at trig....Thanks for pointing it out.

I've done more math with this game then i have in the last year.

[Grizzlol]

I realised this after I posted that, which makes me wonder why that calculator does not advice for 90 degree launches. I guess he who made it did not come to think of that either, which is actually kind of silly.

[Kosmo-not]

I realised this after I posted that, which makes me wonder why that calculator does not advice for 90 degree launches. I guess he who made did it not come to think of that either, which is actually kind of silly.

It's not silly if you know what the ejection angle means.

[felixar90]

I don't think it would. With a 90 degree heading, all you have to do is flip olex's ejection angle diagram left-to-right to get the correct ejection parameters. It also has the advantage of a speed boost from Kerbin's rotation.

And the disadvantage on a trajectory curved away from where you're going...

To have the right trajectory, you need a an ejection burn on the dark side of Kerbin. The optimal ejection for inner planets can only be achieved with an heading of 270º. There is probably a point where the required correction overcome anything you gained by launching at 90º

[Grizzlol]

You could flip the phase angle too. Then you would be doing the ejection burn on the dark side at 90 degrees and the trajectory would be curving the correct way. This would, however, probably only be good if the target orbit is near perfectly circular since lining up with an elliptical orbit obviously would take less fuel when going to the closest point of the orbit in relation to self, which this calculator does take into account if I remember correctly.

To be sure to actually get to the target, it would probably be best to follow the advice of the calculator, unless you want to calculate things yourself. It may not give you the optimal route, though. The developer of that particular program said himself that it is not finished. It only just was configured for the new celestial bodies added in 0.17 and the game itself is not even close to being finished after all.

Edited September 24, 2012 by Grizzlol

[Kosmo-not]

And the disadvantage on a trajectory curved away from where you're going...

To have the right trajectory, you need a an ejection burn on the dark side of Kerbin. The optimal ejection for inner planets can only be achieved with an heading of 270º. There is probably a point where the required correction overcome anything you gained by launching at 90º

You're wasting around 400 m/s by launching on a heading of 270°. There is no disadvantage to launching eastward.

The only things that matter for an interplanetary transfer burn are the velocity you are going at the inner edge of Kerbin's SOI and the direction you are going relative to Kerbin at that moment. Since you are in an equatorial orbit, you can time your burn to have any exit direction you want on the equatorial plane.

So, the only difference between a 090° and a 270° orbit is that 270° requires about 400 m/s more.

[RoboRay]

Ok, this argument again (people suggesting launching at 270). Let's try a different tack...

If launching westward really is better for heading to "inner" destinations, why have all real-world probes sent to Venus launched to the east?

[blueshirt21]

Well, I spent hours yesterday trying to get there, even entering debug and giving myself infinite fuel in a futile attempt to get there. I have no idea what I am doing. No matter how much I try, I just can't get an encounter.

At this point, I don't even care about efficiency-I just want to get there.

Edit: NEVER MIND. I can't read.

I kept thinking 270 degree heading meant 270 degree inclination, so I was kinda going the wrong way. Making a map of Gilly as I type.

Edited September 24, 2012 by blueshirt21

[Person012345]

STOP! Why are people talking about launching into a 270° orbit? That's just silly.

It sounds like you are not doing your ejection burn at the correct angle. Remember that the ejection angle is the angle between where you want your trajectory to take you and the ejection point.

The interactive thingymajig does specify a retrograde orbit and my rocket is perfectly capable of it, but I do still seem to have the same problem as the OP. I tried a couple of times and both times after correcting the inclination (and before), the trajectory ends up nowhere near where I want to go. My interplanetary stage uses 4 nuclear engines, so I figured it was because my ship was a little sluggish in the acceleration department, so I corrected for it the second time, but still ended up out of the way. I think I know how to fix it for next time (bringing the orbit inwards, then burning retrograde until I encounter the planet), but that's going to use more fuel than I am hoping for. The problem for the second flight was that after I brought the trajectory inwards I wasn't certain if I was going to arrive ahead of the planet or behind it, as it turns out I was ahead. But yeah, after the initial burn I seem to end up not-remotely in the orbit of eve.

Although do note I am very terrible at interplanetary travel and maths and such. That being said, I managed to get to duna with the thing (although that was also slightly off, I'm willing to put that down to errors with regards to me than the advice given by the interactive trajectory thing as it was pretty close and was relatively easily fixed with a quickish outward then retro burn).

Well, I spent hours yesterday trying to get there, even entering debug and giving myself infinite fuel in a futile attempt to get there. I have no idea what I am doing. No matter how much I try, I just can't get an encounter.

At this point, I don't even care about efficiency-I just want to get there.

I didn't make it work yet, but I'm pretty sure that if I brought it in (that is, burning towards the sun) until the orbits actually crossed, then burnt retrograde, I would have hit eve. Maybe try that yourself?

If you don't care about efficiency, I have gotten myself to eve before simply by escaping kerbin, bringing myself into a slightly elliptical orbit around the sun with the periapsis touching eve's orbit then waiting.

Edited September 24, 2012 by Person012345

[Grizzlol]

As far as I am concerned, there is quite a critical part missing from the calculator; the assumed thrust to weight ratio or acceleration (either would probably be as good) at the point where you are supposed to start the ejection burn. Spending too much time accelerating will result in the ejection angle not actually be what you want it to be and guesstimating how much ahead of it you should start is no good. In fact, if the spacecraft were to be extremely weak, it would just circle around the origin body in increasingly wider deformed circles. For this reason, the ejection velocity is almost completely irrelevant. It completely depends on the time it takes to reach that velocity to begin with, as the gravitational forces constantly change your speed. Besides, it is better to look at the map anyway.

Whenever I manage to find an encounter without corrections where it is supposed to be happening, which is rare, my velocity compared to the given ejection velocity is still off by hundreds. This was especially noticeable for me when I tried using only three of the new low-thrust nuclear engines that will not even run at full thrust without exploding on a heavy craft. My trajectories suddenly were off so much it could not be corrected in a reasonable fashion. I think this is one of the biggest problems most people who are trying this method have, other than not knowing how to actually correct the trajectory when it is not perfect, which it never is.

I do not mean to criticize the calculator as it still does a good job of getting you where you want to, but I feel like it is incomplete and not accurate enough (the game itself does not allow for extremely high accuracies either, though). I hope there will be tools in-game which help predict the encounters. Getting to planets beyond Jool, assuming that there will be any, would be very difficult at this stage. Trying to get there using gravity assist would be even harder.

Edited September 24, 2012 by Grizzlol

[PictoKong]

Trick with the calculator: instead of the velocity, use your eyes!

I mean: when the apopasis/periapsis (kerbol relative) is aligned to the planet you are trying to reach, you should have an encounter displayed (set the max patched to 3, to get it in Kerbin's SoI). If not, plnace change once there and you should see it. I usually start at the required angle or a bit before (ejection angle, that is) but my interplanetary stage is pretty powerful... also, be sure the planets are correctly placed (i use adamKSP, really useful for thoses kinda things. Lastly, quicksave a bit before you start your burn (like one orbit) so you can quickload if you mess up. This is the only way (collision) to make it to planets and back with stock parts and not overly powerful rockets. Juno for exemple... you can't waste THAT much fuel since it costs a lot just to get there in the first place