Stranded on the Moon.

[Bodrius]

So I made my first trip to the moon, and after a few failed attempts I'm finally orbiting it. Now I want to return home, but I'm unable to select Earth as target in the Transfer screen of the MFD... What am I doing wrong?

 

[Pquardzvaark]

Well, wecome aboard!

Might I suggest instead using TransX? Transfer MFD seems to give me all sorts of problems with this too.

Once you get into lunar orbit, select TransX, and select an eject plan and continue. The next stage should be the area dominated by Earth. Anyway, go plan for a pretty decent retrograde burn - the distance to Earth won't really matter so long as the hypothetical ellipse looks to be fairly close to it.

I hope this explains things but I can try and get more in detail if you still need help.

And have fun orbiting!

 

[Kaito]

ah, yes, this old problem. I've run into this also.
I have a tutorial (its not on orbit hangar) that will tell you how to get back. PM me you e-mail and i'll send it to ya

 

[Tommy]

See this thread.

http://orbiter-forum.com/showthread.php?t=7390

 

[n72.75]

So I made my first trip to the moon, and after a few failed attempts I'm finally orbiting it. Now I want to return home, but I'm unable to select Earth as target in the Transfer screen of the MFD... What am I doing wrong?

Call a cab

 

[Clavius0712]

I seem to remember it involves using IMFD "Planet Approach" to approach Earth, coupled with IMFD "Orbit Eject" to escape the Moon's gravity.

 

[T.Neo]

So I made my first trip to the moon, and after a few failed attempts I'm finally orbiting it. Now I want to return home, but I'm unable to select Earth as target in the Transfer screen of the MFD... What am I doing wrong?

Transfer MFD can't get you out of lunar orbit. You need an MFD like TransX or IMFD.

Returning to Earth from the Moon is rather easy with TransX, and it'll give you a firm basis for doing any further flights with it.

Many happy returns!

EDIT:
I'll recommend these tutorials for TransX:
http://flytandem.com/orbiter/tutorials/

And specifically this one for lunar returns with TransX:
http://flytandem.com/orbiter/tutorials/lunar_return/index.htm

 

[atuhalpa]

You don't need anything but orbit MFD. Just do a burn when the Moon is between you and the earth. Make the burn long enough so your orbit goes "open" and you escape the Moon's sphere of influence (watch the orbit MFD at the bottom) once you have escaped the Moon's sphere of influence (numbers turn red) burn retrograde til your orbit's perigee is really close to earth, then push the "AR" button on orbit MFD, and enter the Earth's sphere of influence (once again watch the bottom of orbit MFD). Once you are captured by the Earth, burn retrograde til you are maybe 500 km perigee. Coast to perigee and make another retrograde burn there til your orbit is circular. It is really easy to be captured by the Earth. It is a cakewalk to get home from the moon.

 

[RSWingman]

If you don't have the fuel to circularize your Earth orbit, you could try Aerobraking.

If you can get your perogee just right (maybe 90k alt?), then roll upside-down and use lift & drag to keep you in the atmosphere & slow you down until your apogee comes down.

It doesn't cost much fuel to make the small corrections to keep your Pe right on approach.

---------- Post added at 02:14 PM ---------- Previous post was at 12:30 PM ----------

Make that 72K alt.

I took off from the Lunar surface with an XR5, with about 20% fuel, 30 days of LOX, 50% RCS & APU.

Burned prograde until the orbit broke, coasted and tried a 90k approach. Did a couple more passes until I found 72k to be about right for aerobraking. Rolled upside-down and held 0 deg climb until circular.

Orbited until I got the right alignment and entered for Habana. Ended up at Canaveral with about 1% fuel left.

 

[Tommy]

The aerobrake technique is shown in my "Home Direct" tutorial. It starts at Brighton Beach, and ends with a dead stick landing at Cape Canaveral. Flight is performed in an XR-2, which is required to view the playback. IMFD is used to navigate to Earth, and AerobrakeMFD is used during re-entry, but neither are required for viewing. If you don't have an XR-2, the PDF manual will tell you how to set the course, etc.

[ame="http://www.orbithangar.com/searchid.php?ID=3660"]Home Direct[/ame]

Just do a burn when the Moon is between you and the earth.

That's not always a good choice for the ejection burn location. Remember, that your ejection vector is not going to be on the opposite side of the moon, it will be about 25 - 30 degrees off prograde (at the time of the burn). It's efficient, but slow, if you are in a retrograde (westward) lunar orbit. Then your lunar escape velocity turns into an Earth retrograde direction, with a slight inward component. If you are in a prograde lunar orbit, it's slow and very inefficient. Your lunar escape vector is along your Earth prograde vector, so you'll have to remove all that velocity plus more to get to Earth.

A good time for the lunar ejection burn is just after "Earthrise". Wait until the Earth has come one full width above the horizon and burn prograde. It's average efficiency, and faster, since your lunar escape velocity becomes Earth inward velocity. It also works in any lunar orbital inclination - prograde, retrograde, even polar.

 

[atuhalpa]

Tommy, thanks for the clarification. I was just giving the general concept as I believe that a lot of the enjoyment in Orbiter, at least for me, is understanding the relationships between an orbit and all the vectors involved and the gravity wells and the velocities. I feel that if one doesn't go out and try a few missions just "winging it", you'll never really understand what you are doing.

 

[Tommy]

That's true, and a stock DG can take as long as it wants to get somewhere (and has rather extravagant Delta-V budget!)

 

[ar81]

[ame="http://www.orbithangar.com/searchid.php?ID=3403"]Tutorial: Concepts for Interplanetary MFD 4.2.1[/ame]