Flight Question From the Moon to Earth

[atuhalpa]

I have been using Orbiter for quite a while now, but I realized that I don't know how to get from orbiting the Moon back to Earth. What tutorial would cover that?

 

[tblaxland]

There is a tutorial on jarmonik's page (http://koti.mbnet.fi/jarmonik/Orbiter.html - scroll down about halfway) on getting from the Moon to the Earth using IMFD. It was written for an older version, but with a little playing around you should be able to get it.

 

[Scarecrow]

You can also do it with TransX, though I'm not sure where to find a tutorial. And another option is to just wait until you're on the opposite side of the moon from the earth, and then burn till you escape, plus some more, and then adjust your orbit later.

 

[atuhalpa]

Yeah I actually know how to get back to earth cause as you say all I have to do is get near earth's gravity well and fall in. But I am giving a tutorial over teamspeak and I want to be able to teach it by the numbers as it were. I can get all over the solar system using DED reckoning, trans-x, and IMFD map mode, but that kind of navigation is hard to teach. I tried using transfer MFD but there doesn't seem to be a mode that allows transfer from the moon to earth. I will brush up on IMFD tutorials as I have been slacking off in learning IMFD. I learned trans-x early on and that has been all I have needed. Thanks for the info.

 

[HiPotOk1978]

I tried using transfer MFD but there doesn't seem to be a mode that allows transfer from the moon to earth.

The reason there isn't a mode that allows transfer from the moon to earth is because your still orbiting around the earth. The simple way to answer this is you need to get away from the gravity influences of the moon and the lower your earth-centric orbit. Now this is a quick and dirty way to do it and by all means this is not fuel efficient is to wait until you can see the earth, aim right at it and burn your engines until OrbitMFD shows your moon-centric eccentricity is greater than 1 and coast.

For a more detailed and slighty more fuel efficient method:
You may know that when your in orbit around the Earth and you want to raise your orbit you aim prograde and burn your engines. If you want to lower your Earth orbit you aim your engines retrograde and burn them. Now again when your orbiting the moon, your also orbiting the earth. It can get quite complex but if you burn retrograde (from the perspective of your earth-centric orbit) you can do two things at once. First you can reach escape velocity from the moon leaving it behind. Second you can also lower your earth-centric orbit getting yourself closer to the Earth. I plan to write a paper about this with pictures and maybe I can even get Epsilon to make a video based on this. I do see quite a bit of questions about Moon/Earth transfers and I also see a need in this department on a good reliable theory paper as well as some video's and TransX/IMFD turorials. Hopefully I will have something together soon

 

[EtherDragon]

Returning to the Earth from the Moon isn't too tough if you think about it a smidge. Here are some goals of such a trip:

1. Leave the Moon's SoI heading in a direction that takes you to earth.
2. Conserve fuel with the most efficient course.

To accomplish #1, you could just thrust prograde until your Moon orbit eccentricity is > 1. You'll eventually leave the Moon's SoI and the Earth will tractor beam you in with it's gravity. Although, out by the moon, the Earth's Gravity isn't all that strong, and it will take a while.

The second goal is where we find the Lunar-return trajectory rosetta stone. Indeed, this technique can be used for any planet escape where you wish to achieve an orbit that takes you closer to your orbiting body's parent (Mars back to Sun for Earth Departure, for example)

To achieve the second goal, we'll use a Hohmann Transfer Orbit. The very same orbital maneuver that we used to get to the Moon in the first place! But, this time, we're around the Moon, and the "high" point of our Hohmann Transfer will be the point where we leave the moon's SoI, and end up between the Moon and the Earth.

I cooked up some bad diagrams to give you two examples of how to accomplish your task:

In this diagram we are orbiting the Moon "Prograde." That is, our orbit about the moon is in a similar direction to the Moon's orbit about the earth.

At point A, the farthest point from the Earth, we make a Prograde Burn until our ecc is just barely > 1. We will orbit about the moon until we reach point B, where the Moon's gravity will be so weak and our velocity such that the Moon leaves us behind. A Mid-Cource-Correction (MCC) at this point sends us Earthbound.

At point C, we burn retrograde for circularization, and we're home.

In this diagram we are orbiting the Moon retrograde, that is, our orbit about the moon is opposite the Moon's orbit about the Earth. This orbit is a favorite of Free Return Trajectory lunar voyages.

At point A, again, furthest from the Earth, we thrust prograde to execute a Hohmann Transfer to point B, between the earth and the moon.

At point B, we've again left the Moon's SoI, and make an MCC to orient our desired aproach to earth.

At point C, we make our Circularization burn, and we're home.

It's really that simple. Simple enough to be done with the Transfer MFD, Sync Orbit, and Align Planes MFDs.

 

[dbeachy1]

Like any other Orbiter mission, different parts of the mission require different MFDs -- you don't need to have all three up at the same time. For example, during ascent to the ISS you'd need all these MFDs: 1) Align Planes, 2) Orbit, 3) Sync Orbit, and 4) Docking. Just bring up the appropriate MFD as you need it.

 

[FordPrefect]

atuhalpa, if it is of any help, you can find an AMSO 1.18 scenario attached to this post, which I had saved after fiddling around with IMFD a lot. It is about 30 minutes prior Apollo 17's TEI burn, just engage auto-burn mode. This scenario runs fine with IMFD50 version, not sure on the other versions.

Your scenario dealer...

 

[Tommy]

Here's a tutorial (with annotated Flight Recordings, and a PDF) for the XR-2 that covers the entire trip from Brighton Beach to Cape Canaveral using IMFD 5.1m. While it's primarily intended to demonstrate the inverted direct re-entry technique, it also covers planning the lunar launch and TEI with IMFD.

For the re-entry, AerobrakeMFD is also used, but not required to watch the flight.

http://www.orbithangar.com/searchid.php?ID=3660

 

[atuhalpa]

Thanks etherdragon and fordprefect, every bit of info is another part of the puzzle.

And actually I believe that one can get home, because of earths gravity well, with just the orbit MFD. Might I be right?

 

[Tommy]

Yes. Wait until the Earth has just come over the horizon. Let it get about one diameter above the horizon and burn prograde until OrbitMFD shows your orbit change from elliptic to parabolic. Once you've left the Moons SOI, Change the reference to Earth. Once you are within the Earths SOI, engage the prograde AP and wait until the vessel stops rolling. Use linear RCS to find a thrust direction (foreward, inward, etc) that improves your PeA. Then you can orient in the correct direction and use the Main engines to adjust the PeA. It's best to stay a bit high ath this point (PeA > 500k) and make more adjuststments as you get closer.

 

[atuhalpa]

And thanks to Tommy whom I forgot to thank in my earlier post.

 

[polaris149Tiberius]

Here is one on these forums

I dont know why noone knows about this one: (is it because its no good?)

Its been viewed 10,060 times so it might be an ok one to try.

http://orbiter-forum.com/showthread.php?t=1303


"From the Earth to The Moon" an AMSO 1.17 Apollo 11 Full Mission Tutorial Using IMFD 5.1h
By Adam RodrigueZ (polaris149Tiberius)
Date of release: 04-16-2008 at 11:46 AM CST (GMT-6)
Revision 1.02 07-2-2008 at 10:49 AM CST(GMT-6)
Launch platforms: AMSO's AS-506 Saturn V Stack
(Note: This tutorial is for use with ArcSoft's AMSO v1.15 -v1.17 and uses IMFD 5.1h-m)

 

[garyw]

Three MFD's? You can only have two up at a time.

Incorrect. You can have multiple MFD's up.

 

[flytandem]

I have been using Orbiter for quite a while now, but I realized that I don't know how to get from orbiting the Moon back to Earth. What tutorial would cover that?

It's actually the first in the series at
http://www.flytandem.com/orbiter/tutorials/index.htm
#1 Lunar Return.

 

[atuhalpa]

Thanks fly. I just went through it and I actually knew how to use maneuver mode already cause that is how I got to the moon in the first place! I just didn't think about using it to get back, mental block I think.

 

[DarkFact]

Travelling from moon to earth

I have found using the build in MFD's easier to use on small trips. Complicated earth to jupiter, saturn and pluto trips easier with TransX (love transX).

My favorite trips mainly due to how cool it looks as you crest the light sides, is a trip to jupiter or the moon.