Interplanetary Guide to Eeloo

[seyss]

Hello,

When I use the Interplanetary Guide (http://ksp.olex.biz/) to get to Eeloo, it tells me to meet Eeloo in the farthest point possible.

Wouldn't be better to intercept Eeloo at the point below shown in the red arrow? (From Kerbin).

edit: maybe because my ship and Eeloo would be traveling in opposite directions?

Thanks.

Edited April 13, 2015 by seyss

[Starhawk]

The calculator gives a phase angle between Kerbin and Eeloo. That position will repeat periodically, but since Eeloo's orbit is so elliptical, the place where you rendezvous will change.

If you time warp enough, you can get a rendezvous that is much closer and much more efficient. It's just a matter of patience.

Hope this helps.

Happy landings!

[Deutherius]

What Starhawk said. Also, While it will take less dV to get to Eeloo where your arrow is pointing, consider that to stay in it's SOI you will have to accelerate your orbit around Kerbol a lot (and Eeloo has about the same gravity as the Mun and no atmosphere, so gravity braking and aerobraking will not really help you) - compared to the encounter you already have, which will take more dV to get to, but less to inject yourself in Eeloo orbit.

And no, you would not be travelling in opposite directions, you'd still both be going prograde around Kerbol (well, unless you spent some ridiculous amount of deltaV to reverse your orbit )

[Kelderek]

When Eeloo it gets to the spot with the red arrow (Eeloo's periapsis around Kerbol), it will have the highest velocity of any point on its entire orbit. Since it is such a large orbit compared to your transfer orbit, when you rendezvous at the encounter the difference between your velocity and Eeloo's will be the biggest it could ever be. As mentioned above, Eeloo has no atmosphere so slowing down to orbit and/or land on Eeloo will be much harder at that red arrow. The transfer you already have is going to be very good, close to ideal if you want to land on Eeloo. If all you wanted was a flyby without any orbit or landing, then the red arrow spot would be ideal because you wouldn't care about the difference in velocity between your ship/probe and Eeloo - but it would be a very quick flyby.

[seyss]

Thanks. I noticed that. Landed without trouble using the farthest pt.

[Warzouz]

I'm in a mission to Eeloo at the moment. I waited for the correct window but instead of firing at the ejection angle on the equator then do a plane correction at mid course, I fired with an inclinaison. To be able to fire with an inclinaison on the correct ejection angle point, I had to launch with the opposit angle on the other side of Kerbin. I circularised, did half an orbit and eject burn (with high TWR to avoid messing everything). When quiting the SOI, you get you effective inclinasion with the sun, which should match Eeloo's.

In other word, I had to time my launch, rotate to the inclinaition angle then turn right (not east), circularize, do half an orbit to cross the equatorial near the ejection angle. Burn at that point.

I had to redo that several time to get it right. The angle was too steep, or I launched too soon, so I didn't get the correct ejection angle on the other side or Kerbin. On my first attempt, I tried 11° (the inclination of Eeloo's orbit), I ended with 4° outside SOI (too low). The I tried 60° (too high), and finally 25° which seems to be roughly right, (a bit too steep). I corrected at mid course for a 400dv, instead of the usual 1300dv. Arrival in 1 year.

This is my first trip to Eeloo.

[Iron4venger]

The best way to reach eelo I think is to grab a duna - jool - eelo window that happens at day 260.

[celem]

Its also worth remembering that elliptical orbits are very hard to theoretically model, so hard infact that we humans cannot do it in reality for the planet (or minor body...whatever, dont open that can'o'worms) Pluto.

This means that the nice tools we use are damn impressive in being able to get intercepts at all.

To quote Paul Schlyter whose page on planetary location I use for programming kOS:

No analytical theory has ever been constructed for the planet Pluto. Our most accurate representation of the motion of this planet is from numerical integrations. Yet, a "curve fit" may be performed to these numerical integrations, and the result will be the formulae below, valid from about 1800 to about 2100.

I wont include the formula he refers to here, its a wall of math, check the link if you want to appreciate how badass elliptical math can be. Its very very difficult to work with ellipses.

In KSP at least the orbit is known, but its still a complicated procedure to align with it.

Regarding your question about the point indicated by the 'red arrow'. Yes, this would be the cheapest transfer in terms of the injection burn dV from Kerbin. You wouldnt meet it head-on however as you would depart when Kerbin is opposite that point on the other side of the sun to meet it in the same direction, though its increased orbital velocity at this, the lowest point in its orbit, would make it a bit more expensive to drop into orbit around.

Edited April 4, 2015 by celem

[MarvinKitFox]

When transferring from a basically circular orbit to a planet with an eccentric orbit, it is always most cost-effective to rendesvous at the target's apogee.

The delta-v needed to *get to* eeloo is less if you plan to meet it at the red arrow, but remember that you need to match speeds with it at that point, too.

At the red arrow its speed relative to your ship will be greater than meeting it at the far end of its orbit.

Realistically though, for Eeloo, the difference is trivial.

Now if you are heading to MoHo, there is a HUGE difference in meeting MoHo at its perigee vs. meeting it at apogee. Purely due to the intensity of the gravity gradient that close to the sun, of course.

Edited April 4, 2015 by MarvinKitFox