How to get to Eeloo

[willwolvescry]

So far I have had no trouble getting to a majority of the planets with no problem (I need to update my ribbons to include Moho) but Eeloo seems to be the hardest to get to. Anyone know the best way to get there?

[LostElement]

Well, Only time I got to Eeloo is was on accident. I just wanted to do a fly by of jool. When i did, it flung me to Eeloo.

[capi3101]

You'll need to do a plane change at the ascending or descending node. I recommend burning just enough to escape Kerbin's SOI, targeting Eeloo, making the plane change and then making a prograde burn with radial adjustments as needed. When you get the encounter, kick back and relax, 'cause it's going to take a while to get out there. I have probes en route; they will get there - just not any time soon.

[Vanamonde]

Eeloo doesn't require any special techiques, thought its SOI is a small target to hit in proportion to the distance you have to cross to get there. What sort of trouble are encountering?

[celem]

A big part of the hassle for me is getting the first prograde kerbin soi escape burn down. While you want to make an inclination change, it's probably not until a good way down the road and you don't want to suddenly find yourself under-speed and trying to push further prograde from the ascending/descending node (which is like 90 days off the periaps).

Just give it loads of gas, and aim for intercept at the point where eeloo's orbit dips inside jool's.

Edited November 26, 2013 by celem

[Superfluous J]

Bring several thousand dV with you. Say... 5000. While you're in orbit around Kerbin.

Wait until you're at the AN or DN between Kerbin and Eeloo. Ignore where Eeloo is, just make sure that, when viewed from the side, Kerbin is where Kerbin and Eeloo's orbits intersect.

Burn like mad on the far dark side of Kerbin to raise your apoapsis around the sun to meet Eeloo. It'll be at the other side of the orbit from where you are now.

While you're heading out to that apoapsis, set Eeloo as a target. make a maneuver node at your apoapsis point (which should also be at or near an AN or DN) and fix the orbital tilt to match Eeloo. Also set the same node to burn prograde until you see a near encounter with Eeloo. Try to get an acutal encounter but if you can't, just get the two encounter markers as close as possible.

Execute the maneuver node.

Now set a new maneuver node at your periapsis around the sun. Fiddle with it until you have an acutal encounter with Eeloo.

Execute that maneuver node.

Go back around your orbit and meet Eeloo. Burn to get into orbit.

Go crack open a cold one. It's been several years since you took off from Kerbin!

[kurja]

Those plane changes cost a lot of dv - wouldn't the most cost-effective method be to launch from kerbin to an intercept at a point where kerbin's plane intersects eeloo's? But how would one set up such a maneuver...?

When I first tried to go to eeloo I looked up the phase angle at ksp.olex.biz, but that didn't seem to work at all. So I just left kerbin prograde, matched planes and fiddled with some nodes 'till I got an intercept.

[SRV Ron]

Plan an intercept when Eeloo intercepts Jool's orbit. Then, you won't have to make a major plane change in your orbit. Be advised that Eeloo SOI is very small making intercept very difficult.

[Superfluous J]

Those plane changes cost a lot of dv - wouldn't the most cost-effective method be to launch from kerbin to an intercept at a point where kerbin's plane intersects eeloo's? But how would one set up such a maneuver...?

When I first tried to go to eeloo I looked up the phase angle at ksp.olex.biz, but that didn't seem to work at all. So I just left kerbin prograde, matched planes and fiddled with some nodes 'till I got an intercept.

Not sure if you're replying directly to me or not but in case you are, my method actually takes that in to account. You'll eventually need to take that plane change into account, either by burning to actually line up orbital planes or burning to get in to orbit during an encounter. If you do that burning at the furthest point from the sun (aka Eeloo's orbit) then you'll use the least amount of fuel to do it.

If all you're trying for is a flyby, then you don't want to correct for plane angle at all. But you also want to then launch during a window so you hit Eeloo's orbit at the same place and time where Eeloo itself is.

[kurja]

Not sure if you're replying directly to me or not but in case you are, my method actually takes that in to account. You'll eventually need to take that plane change into account, either by burning to actually line up orbital planes or burning to get in to orbit during an encounter. If you do that burning at the furthest point from the sun (aka Eeloo's orbit) then you'll use the least amount of fuel to do it.

If all you're trying for is a flyby, then you don't want to correct for plane angle at all. But you also want to then launch during a window so you hit Eeloo's orbit at the same place and time where Eeloo itself is.

But burning during an encounter to get an orbit costs the same regardless of your inclination, at least I can't see why the required change of velocity would be any different? That's what I had in mind.

[Superfluous J]

But burning during an encounter to get an orbit costs the same regardless of your inclination, at least I can't see why the required change of velocity would be any different? That's what I had in mind.

You are incorrect, tough I'm having a bit of trouble doing the math in my head and I may be incorrect as well. I think I need to do some testing

To get into orbit around an airless body, you essentially have to rendezvous with it. To do that you need to slow down your relative velocity to it in relation to the Sun to 0 (well not quite, but to orbital velocity which for Eeloo is pretty darn close to 0 compared to the velocities you're going around the Sun). So you *do* need to burn to correct any plane changes.

Think of it this way. If you come into the sphere of influence at a crazy angle to Eeloo, you've got some south-north velocity you wouldn't have had relative to it. Also, Eeloo will have some counterclockwise motion (relative to the Sun) that YOU don't have. Those will show up in your Eeloo encounter as velocity that will need to be changed. You won't need to totally kill your south-north velocity because you can use a little of it to orbit. Same for the east-west velocity. But when you add those together, they will be very very close to the vector you could have burned to do the plane change maneuver plus another maneuver to circularize your orbit to match Eeloo's.

What I don't know is if doing the maneuvers individually (as I suggest) imparts a delta-V loss inherent in doing two maneuvers over 1. If you walk a mile north and a mile west, you walk 2 miles. But if you walk 2 miles north-west, you'll go farther. I think perhaps the same is true in space but I don't actually know.

Time for some testing.

[kurja]

You are incorrect, tough I'm having a bit of trouble doing the math in my head and I may be incorrect as well. I think I need to do some testing

To get into orbit around an airless body, you essentially have to rendezvous with it. To do that you need to slow down your relative velocity to it in relation to the Sun to 0 (well not quite, but to orbital velocity which for Eeloo is pretty darn close to 0 compared to the velocities you're going around the Sun). So you *do* need to burn to correct any plane changes.

Think of it this way. If you come into the sphere of influence at a crazy angle to Eeloo, you've got some south-north velocity you wouldn't have had relative to it. Also, Eeloo will have some counterclockwise motion (relative to the Sun) that YOU don't have. Those will show up in your Eeloo encounter as velocity that will need to be changed. You won't need to totally kill your south-north velocity because you can use a little of it to orbit. Same for the east-west velocity. But when you add those together, they will be very very close to the vector you could have burned to do the plane change maneuver plus another maneuver to circularize your orbit to match Eeloo's.

What I don't know is if doing the maneuvers individually (as I suggest) imparts a delta-V loss inherent in doing two maneuvers over 1. If you walk a mile north and a mile west, you walk 2 miles. But if you walk 2 miles north-west, you'll go farther. I think perhaps the same is true in space but I don't actually know.

Time for some testing.

I see what you mean, but in ksp the rest of the universe ceases to exist once you enter a body's soi - it's just the planet and you coming towards it. Does the velocity from inclination difference carry through over there, I do not know.

[Kasuha]

To get into orbit around an airless body, you essentially have to rendezvous with it. To do that you need to slow down your relative velocity to it in relation to the Sun to 0 (well not quite, but to orbital velocity which for Eeloo is pretty darn close to 0 compared to the velocities you're going around the Sun). So you *do* need to burn to correct any plane changes.

In fact, usually when encountering Eeloo your Solar orbital velocity is smaller than Eeloo's because you're on lower orbit so Eeloo is catching up to you. So I wouldn't say its orbital velocity is zero.

Also when killing your inclination difference together with matching Eeloo's orbital speed you're saving dv compared to if you're killing the two velocity components separately.

[Superfluous J]

I see what you mean, but in ksp the rest of the universe ceases to exist once you enter a body's soi - it's just the planet and you coming towards it. Does the velocity from inclination difference carry through over there, I do not know.

It does. Try this:

Go to Mun, and as soon as you enter Mun's SOI look at your orbital velocity relative to Mun. Revert the flight, and launch again but this time go WEST from KSC so you're orbiting Kerbin backwards. Then go to Mun and look at your orbital velocity relative to Mun.

How fast you're going relative to the new SOI is taken into account when you go there.

In fact, usually when encountering Eeloo your Solar orbital velocity is smaller than Eeloo's because you're on lower orbit so Eeloo is catching up to you. So I wouldn't say its orbital velocity is zero.

Sorry for not being more clear. I wasn't talking about encountering as much as orbiting. Yes, you're almost always going slower than Eeloo relative to the Sun when you encounter it.

Also when killing your inclination difference together with matching Eeloo's orbital speed you're saving dv compared to if you're killing the two velocity components separately.

That's what I was suspecting (kind of like my "walking north, then walking west" scenario) and testing did confirm it.

However, my steps take that into account, as I said:

While you're heading out to that apoapsis, set Eeloo as a target. make a maneuver node at your apoapsis point (which should also be at or near an AN or DN) and fix the orbital tilt to match Eeloo. Also set the same node to burn prograde until you see a near encounter with Eeloo. Try to get an acutal encounter but if you can't, just get the two encounter markers as close as possible.

So I still stand by my way of doing it

[Kasuha]

However, my steps take that into account, as I said:

...

So I still stand by my way of doing it

There's no point to match the inclination if you already have an intersect. It won't bring you any more opportunities for rendezvous and when you brake at Eeloo you'll be on inclined orbit anyway. In fact, if you keep Kerbin inclination instead and manage perfect rendezvous with Eeloo you'll be on equatorial orbit.

[Superfluous J]

There's no point to match the inclination if you already have an intersect. It won't bring you any more opportunities for rendezvous and when you brake at Eeloo you'll be on inclined orbit anyway. In fact, if you keep Kerbin inclination instead and manage perfect rendezvous with Eeloo you'll be on equatorial orbit.

That assumes (at least) 2 things:

You have good TWR (More important for Moho than Dres and Eeloo, but it still matters). Why do a 10-minute burn to get into orbit when you can do an 8-minute burn to get an encounter and a 2-minute burn to get into orbit?

You have pinpoint accuracy. If your orbit is tilted, you have less time while encountering the body to get into orbit, and must be more accurate when aiming at it in the first place.

I've found that minimizing my burn time at periapsis makes me a very happy man, and maximizing my time in the SOI of my target makes me happier still.

[Kasuha]

Why do a 10-minute burn to get into orbit when you can do an 8-minute burn to get an encounter and a 2-minute burn to get into orbit?

You're likely to use two burns in any case. One to get an encounter, one to get to orbit. The question is whether it is worth it to fix your inclination in the first one. In my opinion it is not. Especially if you want to end up in equatorial orbit.

You have pinpoint accuracy. If your orbit is tilted, you have less time while encountering the body to get into orbit, and must be more accurate when aiming at it in the first place.

We already have this pinpoint accuracy since we got maneuver nodes. I quite often plan Laythe aerobraking while still in Kerbin SOI. Of course it requires a few corrections en route but the required accuracy is available to be planned and maintained.

And since SOIs are spheres, the angle at which you enter them doesn't matter. The speed does, but the speed difference caused by kerbin/eeloo inclination difference is next to negligible.

---

Edit: after a short maths session I take back one thing I said earlier: you won't end up on Eeloo equatorial orbit if you stay at Kerbin inclination. In fact if you do so your resulting orbit will be inclined by at least Eeloo's orbital inclination. Unless you fix it during braking.

However.

1/ When braking near Eeloo, you still have Oberth on your side. Which is not the case when you're fixing the orbit in interplanetary space without anything nearby.

2/ Fixing your orbital inclination before meeting Eeloo will decrease your Eeloo SOI entry speed by whopping 1%. Totally not worth it IMO.

Edited November 28, 2013 by Kasuha

[Superfluous J]

1/ When braking near Eeloo, you still have Oberth on your side. Which is not the case when you're fixing the orbit in interplanetary space without anything nearby.

2/ Fixing your orbital inclination before meeting Eeloo will decrease your Eeloo SOI entry speed by whopping 1%. Totally not worth it IMO.

That's fair, and all we've been talking about are minor differences. I guess mostly it just feels right to have the orbit inclination correct on my approach. Next time I go, I'll not correct and see how that feels.

Oberth doesn't come in to play THAT much on the smaller bodies, especially if you're going so fast that most of your burn isn't at periapsis. It probably helps about as much as changing your inclination does. (no I haven't done the math)

I will leave you with this, and I am sorry in advance:

I guess I just prefer my AN and DN to be as close to 0 as possible, while you are not quite so...

...inclined.

YEEEEEEEAAAAAAAAAAAAAAH!

[kurja]

It does. Try this:

Go to Mun, and as soon as you enter Mun's SOI look at your orbital velocity relative to Mun. Revert the flight, and launch again but this time go WEST from KSC so you're orbiting Kerbin backwards. Then go to Mun and look at your orbital velocity relative to Mun.

How fast you're going relative to the new SOI is taken into account when you go there.

Sure, going opposite to the body's orbit would make a difference. But that's a 180 degree difference, Eeloo's inclination is 6 degrees - how much would this add to capture burn dv requirement, as opposed to what needs to be spent to match inclinations in solar orbit? If someone more mathematically inclined is reading, would you care to offer some numbers on this =)

[Kasuha]

Sure, going opposite to the body's orbit would make a difference. But that's a 180 degree difference, Eeloo's inclination is 6 degrees - how much would this add to capture burn dv requirement, as opposed to what needs to be spent to match inclinations in solar orbit? If someone more mathematically inclined is reading, would you care to offer some numbers on this =)

2/ Fixing your orbital inclination before meeting Eeloo will decrease your Eeloo SOI entry speed by whopping 1%. Totally not worth it IMO.

Actually it's rather complicated and it depends on what proportion of Eeloo's orbital speed is your (Sun-) orbital speed at the point of encounter. If your speed is about half Eeloo's, then the difference is about 1%. If your speed is less, the difference is even smaller. On the other hand, if your speed is comparable with Eeloo's (i.e. you almost-matched your orbits in interplanetary space) then the difference is rather huge as with matching orbital planes you enter at next to zero speed and basically freefall on Eeloo, while without matching orbital planes you come at about 10% of Eeloo's orbital speed.