Flight Question Lagrange points/halo orbits? Are there any methods?

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mikusingularity
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I have seen multiple mission profiles for cislunar operations that involve placing infrastructure or rendezvous with vessels around the Earth-Moon L1 or L2 points (e.g. the Exploration Gateway Platform concept), and I want to know if there's any known method for doing that in Orbiter.
 
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ISProgram

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I um, wasn't aware Orbiter was capable of recreating Lagrangian points without an add-on...
 

Keithth G

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Since, Orbiter models Newtonian gravity really rather well, Lagrange points are very much part of its core gravity model.

However, there are (as far as I know) no tools that map trajectories to or from the Lagrange points and, in particular, there are no tools that map halo trajectories around the Earth/Moon L1 and L2 - taking into account the elliptical orbit of the Moon around the Earth, and Solar perturbations. This could be done in Orbiter, but no-one has got around to doing it so far.

There is also the issue that even if one has a map of the halo orbits, there isn't the software that allows one to do the necessary 'station keeping' to keep you on a halo orbits. (Halo orbits are unstable - a bit like balancing on a knife edge. Staying there is an active process.)
 
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This [ame="http://www.orbithangar.com/searchid.php?ID=3644"]MFD[/ame] seems to show halo trajectories, but I haven't tried it yet. What I need is a method for getting there in the first place.

How unstable are they? Could a craft stay in about the same space for a week or two temporarily for a mission?
 

ISProgram

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I think so, yeah. The (simpler) way I heard a halo orbit works is that the spacecraft is never really orbiting said point; rather, it's drifting away or towards the point at any point in time. It could leave the point and go into heliocentric orbit at any point if this drifting was allowed to continue uninterrupted. "Stationkeeping", however, is when it reaches the comfortable outer limit of its orbit drifts too far, the propulsion is used to send it in the opposite direction, until it reaches the farthest distance on the opposite side, vice versa. This is probably all wrong ._.

Most halo orbits have a "period" of a few months; keeping an object there for <1 month shouldn't be an issue.

---------- Post added at 06:41 AM ---------- Previous post was at 06:38 AM ----------

Now that I think about it, is this part of that Hatsunese manned moon landing plan that's been around?
 

Keithth G

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The 'textbook' way of getting to a halo orbit is to calculate the stable manifold for that orbit. The stable manifold is a kind of 'tube' that extends away from the halo orbit.

If you get onto the tube, with the right speed and heading (calculated alongside the calculation the location of the stable manifold), then you can switch off your engines and let gravity give you a free ride all the way to the halo orbit. Once on the halo orbit, then you can do your station keeping to keep you there.

To calculate the location of the halo orbits and their stable manifolds requires some significant computational 'grunt' work. It can be done within Orbiter - its just that no-one appears to have done it so far.

Halo orbits are stable for periods of a week or two. After that, there will be a very rapid 'escape' from the halo orbit.
 
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fred18

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Hi, i can just be a quick spot since i'm out now, but i remember to have used the gaia addon, which put the gaia telescope on the earth sun lagrangian point, and it uses an mfd to do that, you might want to give it a check. Since i'm out i can't give any more details, in case i'll look for it and will send u
 

boogabooga

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In the past, I have sort of hacked my way out to Lagrange points with IMFD course program in offset mode, where the offset points to about where I knew the Lagrange point would be. (You find the equations on Wikipedia, etc.)

Also found some advice in this add-on:
[ame="http://www.orbithangar.com/searchid.php?ID=6730"]DSCOVR[/ame]

The IMFD map can be useful, if you know what you are looking for.
 

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In the "Eyes Turned Skyward" alternate history timeline, humanity returns to the Moon three decades after Apollo with the Artemis program. Notice how the undocking and rendezvous of (an evolved version of) the Apollo CSM and the Artemis lander takes place in an EML2 halo orbit? What if someone wanted to recreate that mission or mission profile? This is for a two-week sortie, by the way.

artemis_conops.png
 
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As seen in this NASASpaceflight forum thread, the main benefits of staging a lunar mission at a halo orbit around the Earth-Moon L2 point instead of low lunar orbit are:

- line-of-sight communications from a landed spacecraft on the far side of the Moon, without the need for extra relay satellites
- "global access" to just about any landing site on the Moon (with minimal variance in the delta-v requirement), with a better "anytime return" capability because to do that with a low Lunar orbit rendezvous would require major orbital plane changes, which is why that mission profile is only limited to near-equatorial or polar landing sites.

The stationkeeping requirements are 400 ft/s (120 m/s) of delta-v per year. I haven't tried it yet, but maybe [ame="http://www.orbithangar.com/searchid.php?ID=4582"]this MFD[/ame] can be used to "teleport" the vessel (as described [ame="http://www.orbithangar.com/searchid.php?ID=4581"]here[/ame]) instead of having to switch to the vehicle all the time.

Getting to the lunar surface from the L2 point requires 2520 m/s of delta-v compared to 1870 m/s for low Lunar orbit.

Also, a lunar swing-by would be required to reduce the delta-v of arriving at the L2 point. Direct insertion would need 1230 m/s, while a lunar swingby would involve a 184 m/s maneuver at closest approach, and a 148 m/s maneuver at L2 arrival (total of 332 m/s). But does anyone know how to do that in Orbiter?
 
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Keithth G

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Also, a lunar swing-by would be required to reduce the delta-v of arriving at the L2 point. Direct insertion would need 1230 m/s, while a lunar swingby would involve a 184 m/s maneuver at closest approach, and a 148 m/s maneuver at L2 arrival (total of 332 m/s). But does anyone know how to do that in Orbiter?

To do this, I suspect that you will have to build your own integration engine and do the necessary calculations outside of Orbiter. In effect, you have to build your own, personal MFD to do this.

In general, it isn't hard to imagine how one one would do this in principle: we know that we start from Earth and swing by the Moon in the Earth/Moon orbital plane; then from the Moon we swing up to L2. This means that we have two trajectories to splice together at the Moon - with, presumably, a small prograde/retrograde burn at the patch point. One would use some form of differential correction algorithm to ensure that the necessary boundary conditions were met; and that the total delta-v of the burn at Moon encounter and then at L2 is minimised.

There is a fair amount of computational 'grunt' required to set this up, but it can be done.
 
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boogabooga

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To do this, I suspect that you will have to build your own integration engine and do the necessary calculations outside of Orbiter. In effect, you have to build your own, personal MFD to do this.

In general, it isn't hard to imagine how one one would do this in principle: we know that we start from Earth and swing by the Moon in the Earth/Moon orbital plane; then from the Moon we swing up to L2. This means that we have two trajectories to splice together at the Moon - with, presumably, a small prograde/retrograde burn at the patch point. One would use some form of differential correction algorithm to ensure that the necessary boundary conditions were met; and that the total delta-v of the burn at Moon encounter and then at L2 is minimised.

There is a fair amount of computational 'grunt' required to set this up, but it can be done.

There is already an open source "integration engine" with Lagrange point support:
https://gmat.gsfc.nasa.gov/

Incidentally, it was just updated a few days ago.
 

AssemblyLanguage

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Off topic but gmat.gsfc.nasa.gov uses an invalid security certificate.

The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported.

Has anyone had any problems with this site?
 

Mandella

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This MFD seems to show halo trajectories, but I haven't tried it yet. What I need is a method for getting there in the first place.

I might be misunderstanding what you need here, but have you tried teleporting a "dummy" ship to one of the Lagrange points and then using IMFD or Transx to plot an intercept to the dummy?

This is the way I usually transit to the O'Neal stations I have in my system, although I suspect that this method is too fuel wasteful to be useful for the contemporary tech you are using.
 

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Although I never did that before, I could potentially do that, but what I really need is something that can keep a vessel fixed at the Lagrange point so I don't have to go back and click "GO" again and again.

Also, I need a reliable method to do that "lunar flyby maneuver to reduce delta-v."
 

Keithth G

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What you need is, it would seem, an automated 'station-keeping' widget that can run in the background and that will keep your craft 'on station' at L2.

I would like such a widget too.
 
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boogabooga

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I might be misunderstanding what you need here, but have you tried teleporting a "dummy" ship to one of the Lagrange points and then using IMFD or Transx to plot an intercept to the dummy?

This is the way I usually transit to the O'Neal stations I have in my system, although I suspect that this method is too fuel wasteful to be useful for the contemporary tech you are using.

Useless, as neither IMFD nor TransX will account for a target under the influence two gravity sources. Even if the IMFD map knows to simulate your trajectory as an n-body problem, the same is not necessarily true of you target.
 
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