OK, this thread and the question of planning a Moon-Earth-Mars trajectory has been bugging me for weeks. So, after much fiddling with TransX, I found a way to do it....kind of. It's a bit complicated, but might be of interest to TransX buffs....
It still involves a little "eyeballing" - once the escape trajectory from earth is planned you need to estimate the mid-point on the Moon's orbit between the two points where the escape trajectory intersects the Moon's orbit. This is the point of departure from the Moon.
And a little "trick" for accessing the Manoeuvre Mode in a stage where you can't usually do so - go back to the previous stage and select Manoeuvre Mode, then go forward to the next stage and you can still access Manoeuvre Mode.
For simplicity I started from a roughly equatorial Lunar orbit. The inclination is not crucial, however for large inclinations the LAN should be close to 90 deg away from the Earth-Moon line at the time of departure from the Moon, in order to make an efficient Moon-Earth transfer. Launch from the Moon surface or adjust your
orbit with this in mind.
General Outline
The method uses 3 stages:
1st stage - Moon centered, manoeuvre mode used for escape burn
2nd stage - Earth centered, manoeuvre mode used for escape burn
3rd stage - Sun centered, Eject Plan used to plan escape trajectory from Earth
First, an initial "rough" trajectory from Earth to Mars is planned in the 3rd stage using the Eject Plan. The planned escape trajectory is visible in the 2nd stage.
The date chosen for escape from Earth may not be suitable for the Moon-Earth transfer, so the nearest available Moon-Earth transfer window is found by setting up a manoeuvre in 1st stage and adjusting the time of manoeuvre so that the departure from the Moon seen in the 2nd stage is mid-way on the Moon's orbit between the points where the escape trajectory intersects the Moon's orbit. The time of the periapsis with Earth can now be used in the 3rd stage Eject Plan as the eject date, the Earth-Mars trajectory can be refined for this eject date.
A manouevre is created in the 2nd stage at periapsis with Earth to match the proposed Eject Plan trajectory from Earth to Mars.
STEP-BY-STEP
GENERAL SETUP
(TransX version 3.13 used)
Select TransX in both MFDs
Right MFD - Stage1
Click [++] to select "Escape" as target
Click [VAR] six times to select "Advanced" variable
Click [++] to set "Advanced" to On
Click [VAR] twice to select "Autoplan" variable
Click [++] to set "Autoplan" to Off
Click [VAR] to select "Plan Type" variable
Click [++] twice to select "Cruise Plan"
Click [VAR] to select "Plan" variable
Click [++] to select "Eject"
Right MFD - Stage2
Click [FWD] to advance to Stage2
Click [++] twice to select "Escape" as target
Click [VAR] six times to select "Advanced" variable
Click [++] to set "Advanced" to On
Click [VAR] twice to select "Autoplan" variable
Click [++] to set "Autoplan" to Off
Click [VAR] to select "Plan Type" variable
Click [++] to set "Plan Type" to Initial
Click [VAR] to select "Plan" variable
Click [++] to set "Plan" to Escape
Right MFD - Stage3
Click [FWD] to advance to Stage3
Click [++] twice to select "Mars" as target
MARS INTERCEPT - ROUGH SETUP
Right MFD - Stage3
Click [VW] to select "Eject" variables
Click [VAR] to cycle through Eject variables Prograde/Ej.Date/Outward Vel./Ch.Plane Vel.
Click [++] or [--] to adjust the variables' values to intercept Mars.
Example "Eject" variables values:
Prograde 3.549k
Ej.Date 54352.41
Outward -1.802k
Ch.Plane 40
Make a note of the Eject Date.
Wait until 15 days before the Eject Date before continuing (this will avoid unneccesary tweaking and updating while you wait for Eject Date to arrive)
DEPARTURE FROM MOON - ROUGH SETUP (pt.1)
Click [BCK] to view Stage2 in the Right MFD.
You can see your escape trajectory from Earth (dotted yellow line)
Click [++] or [--] to adjust the "Pe Distance" to ~6.700M (or as close to the Earth's atmosphere as you dare).
Left MFD - Stage1
Click [VW] twice to select "Manoeuvre Mode"
Click [++] to set "Manoeuvre Mode" to On
Click [VAR] to cycle through the Manoeuvre Mode variables.
Set "Man.date" variable to your Eject Date(Stage3)
Set "Prograde vel." to ~800m/s
Now you can see your Moon-Earth transfer trajectory (solid green line) in the Right MFD (Stage2)
DEPARTURE FROM MOON - ROUGH SETUP (pt.2)
Adjust the "Man. date" (in Left MFD - Stage1) so that the departure from the Moon (in Right MFD - Stage2) occurs at the point in the Moon's orbit which is half-way between the points where the escape trajectory from Earth intersects the Moon's orbit. Use fine adjustment to set the PeA with Earth to minimum.
Make a note of the "Pe MJD" value in Right MFD (Stage2)
MARS INTERCEPT - EJECT DATE FINALISATION & CLEANUP
Right MFD - Stage2
Click [FWD] to advance to Stage3
Set the "Eject Date" variable to the "Pe MJD" value from Stage2
Adjust the other "Eject" variables Prograde/Outward Vel./Ch.Plane Vel. to get a good intercept with Mars.
DEPARTURE FROM MOON - INCLINATION FINALISATION & CLEANUP
Right MFD - Stage3
Click [BCK] to go to Stage2
Check that the departure from the Moon is still mid-way between the Earth escape trajectory lines (green solid elipse is in the middle of the yellow dotted lines). If not, go back to the section "DEPARTURE FROM MOON - ROUGH SETUP (pt.2)" and repeat procedure.
Left MFD - Stage1
Click [VAR] twice to select "Ch.plane vel." variable and adjust it so that the "Rel Inc" value in the Right MFD(Stage2) is at minimum.
Click [-VR] three times to select "Prograde vel." variable and adjust it so that the "Focus PeD" variable in the Right MFD(Stage2) is the same as the "Pe Distance" value.
You may need to tweak the "Ch.plane vel." and "Prograde" vel." some more until the "Rel Inc" is minimum and "Focus PeD" equals "Pe Distance"
EARTH PERIAPSIS BURN MANOEUVRE - ROUGH SETUP
Right MFD - Stage2
Click [BCK] to go to Stage1
Click[VW] until "View:Manoeuvre" is displayed
Click [VAR] until "Manoeuvre mode On" is displayed
Click [FWD] to advance to Stage2
Click [++] to set "Manoeuvre mode" to On
Click [VAR] three times to select "Man. date" and set it to the "Pe MJD" value.
Click [-VR] to select "Prograde vel." and set it to ~700m/s
You will now see your Earth Periapsis burn trajectory (yellow dotted line) as well as the Mars intercept trajectory (another yellow dotted line).
Adjust the "Man. date" and "Prograde vel." variables so that the trajectories are the same (the yellow dotted lines coincide).
EARTH PERIAPSIS BURN MANOEUVRE - CLEANUP
This procedure will delete your Earth escape Eject plan values, so wait until the Moon departure date is near before commencing.
Right MFD - Stage2
Click [FWD] to advance to Stage3
Click [VW] until "View:Setup" is displayed
Click [VAR] until "Autoplan On" is displayed
Click [++] to set "Autoplan" to Off
Click [VAR] to select "Plan"
Click [++] twice to select "None"
Click [BCK], then click [FWD]
Now you can see the result of your Earth Periapsis burn manoeuvre (solid green line).
Left MFD - Stage1
Click [FWD] to advance to Stage2
Click [VAR] to cycle through the Earth Periapsis burn manoeuvre variables and adjust them to get a good intercept with Mars in the Right MFD (Stage3)
Got that OK? Now, execute the plan!
Hint: You can miss out the last two "EARTH PERIAPSIS BURN MANOEUVRE" sections - once you have made the escape burn from the Moon and are within the Earth SOI, switch over to IMFD "Course - Target Intercept" and "Orbit Eject".
Another Hint: You'll probably need to tweak the Earth Periapsis burn manoeuvre when you're approaching Earth.
Observation: This method saves about 300m/s dV compared to a direct Moon-Mars trajectory, not a huge saving but better than nothing. I guess if you want to go from, say, Europa to Saturn, the dV saved will be greater.
Cheers,
Brian
