Flight Question Most efficient trajectory from LEO to the Earth-Moon L2 point

[BruceJohnJennerLawso]

Hey everyone,

Been planning a project involving flights to the Earth-Moon L2 point, as a precursor to establishing an outpost there. My principal point of confusion at this time is how to get there directly from Earth orbit. My assumption would be that the best trajectory for getting there is a simple loop behind the moon, but I was wondering if anyone can describe for me exactly what it would look like (a diagram would be good).

Thanks in advance :tiphat:

 

[HiPotOk1978]

I would suggest coming from behind the moon instead of in front of the moon like Apollo did. It would seem to me that your have less energy to get rid of once you get there... btw

Are you planning on building a space station at the Earth-Moon L2 point?

If so you might wanna know that even tho its considered a stable Lagrangian point, your still experience drift because of solar wind, Jupiter, non-spherical gravity from the moon (is that simulated?) as well as radiation pressure, and gravity gradient torque, and the other planets will affect you so you will not be able to just park there. Another thing to think about is the sun. Depending on where the moon is at any given time, your be pulled closer to the moon, pull ahead of the moon, pulled behind from the moon, pulled back from the moon and the cycle will repeat over the course of the orbit. Over the course of being in the Lagrangian point, so your have to do correction burns to keep yourself there or any given amount of time. If your looking for a point to refuel your craft may I suggest refueling in Earth orbit as well as in Lunar orbit before you head down to the surface if that is your plan. For a space station in LEO, your have to deal with nodal regression for your launch windows or you can simply launch your fuel container before each launch.

Hope that helped... one long post

 

[dgatsoulis]

My assumption would be that the best trajectory for getting there is a simple loop behind the moon, but I was wondering if anyone can describe for me exactly what it would look like (a diagram would be good).

It doesn't get more descriptive than this.

Simply "parking" at the L2 is not so stable, as HiPotOk1978 already said.
So a [ame="http://en.wikipedia.org/wiki/Lissajous_orbit"]Lissajous orbit[/ame] seems like a good idea but those orbits are not periodic.

A planar Lyapunov orbit or a 3 dimensional Halo orbit are better solutions, they also minimize station-keeping and are periodic.

Jump to sections 3 and 4 in the first link to see the transfers from LEO for both of these types of orbits.

As for how to set it up in Orbiter: I have no idea, but I'll definitely give it a try, after I finish reading that paper.

---------- Post added at 23:15 ---------- Previous post was at 12:09 ----------

Ok, this is very interesting. In the pic below, I'm trying to get to the #4 transfer trajectory, which seems to need the least ΔV for entering the manifold and then ease myself into the Lyapunov orbit around L2.

So far my trajectory looks a lot more like #3. I will definitely need a way to target the L2, but wishbone's lighthouse (IIRC) can do that.

 

[BruceJohnJennerLawso]

It doesn't get more descriptive than this.

Simply "parking" at the L2 is not so stable, as HiPotOk1978 already said.
So a Lissajous orbit seems like a good idea but those orbits are not periodic.

A planar Lyapunov orbit or a 3 dimensional Halo orbit are better solutions, they also minimize station-keeping and are periodic.

Jump to sections 3 and 4 in the first link to see the transfers from LEO for both of these types of orbits.

As for how to set it up in Orbiter: I have no idea, but I'll definitely give it a try, after I finish reading that paper.

---------- Post added at 23:15 ---------- Previous post was at 12:09 ----------

Ok, this is very interesting. In the pic below, I'm trying to get to the #4 transfer trajectory, which seems to need the least ΔV for entering the manifold and then ease myself into the Lyapunov orbit around L2.

So far my trajectory looks a lot more like #3. I will definitely need a way to target the L2, but wishbone's lighthouse (IIRC) can do that.

:huh:

I guess Im in a little over my head there, but Ill start reading the pdf when I get the chance. From what I can grasp there, it sounds like slowly waltzing ones way in from near-L2 orbits is a somewhat more delta-v efficient way to get there?

By the way, couldnt help but notice the redo you made on the orbiter fonts, really quite cool :thumbup:. Would you ever consider uploading that on Orbithangar?

 

[dgatsoulis]

:huh:

I guess Im in a little over my head there, but Ill start reading the pdf when I get the chance. From what I can grasp there, it sounds like slowly waltzing ones way in from near-L2 orbits is a somewhat more delta-v efficient way to get there?

The general idea is that you start from a LEO coplanar with the Moon and you burn a slow transfer (flight-time ~5.5 days). Then you make a burn at Moon periapsis to slow down and get yourself in one of the "manifolds" that lead to a close orbit around the L2 point. Once there it takes one more small burn to stabilize the orbit. I will have time to try and set it up during the weekend.

By the way, couldnt help but notice the redo you made on the orbiter fonts, really quite cool :thumbup:. Would you ever consider uploading that on Orbithangar?

I have so many of those small customizations that would clutter up the O-H if I uploaded them, even more than what it is already. When I make them, I stop when the result is "good enough" for me, so I don't think it's worth the upload.
But I certainly don't mind sharing, so I'll leave a link for a dropbox download: dgatHUD
Unzip in your Orbiter directory and everything will go in it's place. Keep a backup of these:
Textures\font1tex.dds
Textures\Cockpit\ (The whole directory)
This way you can go back to the default if you don't like it.