Question Lunar Transfer mfd help

[mvronsky]

Hi all,
I have been trying to get to the moon and back with a Themis-A launcher plus a CTV-Lunar. Whenever I try to use IMFD I end up getting confused and running out of fuel. I thought of using Lunar Transfer mfd which I used in a tutorial but I am confused on how I set it up and use it. More specifically, I do not understand how I pick the values that I input into the program (TOA, PeT. etc.)

Thanks in advance,
Michael

 

[vsfx]

Hi all,
I have been trying to get to the moon and back with a Themis-A launcher plus a CTV-Lunar. Whenever I try to use IMFD I end up getting confused and running out of fuel. I thought of using Lunar Transfer mfd which I used in a tutorial but I am confused on how I set it up and use it. More specifically, I do not understand how I pick the values that I input into the program (TOA, PeT. etc.)

Hi Michael

Lunar Transfer MFD is absolutely the best and easiest tool to use in getting you from the Earth to the Moon (I find IMFD too complicated as well, I prefer TransX). The main programs in the MFD are:

TLI - Trans-Lunar injection
LOI - Lunar orbit insertion
TEI - Trans-Earth injection

Enter values that you want for PeA, PeT etc. The MFD calculates everything for you when you press the EXE button. (This can be changed to automatically update on the config screen) Then switch to the DV screen and you can select autoburn where you will be put in the correct orientation and the burn will be done automatically. It will even slow time acceleration down. The .pdf file explains more but hope this helps.

I like to use the CTV as well, but if your using the Themis-A to get to orbit and then the CTV for TLI, LOI and TEI things will be very tight. You could use an Ariane 5 with a TLI stage, all available from Orbiter Francophone.

 

[Tommy]

Picking the values is confusing, but not actually that complicated. PeA can be any suitable orbital altitude, 80k - 100k is fine.

The main value to consider is one that LTMFD doesn't show - Time of Flight. When you leave Earth is determined by the Moon's position and the the TOF. You basically set the TOF by setting the TEj and ToA (aka TIn). A shorter TOF requires more dV (thus, more fuel) but allows for an Apollo style free-return trajectory. Start with a TOF of around 78 hours, and adjust as required to attain the desire transfer trajectory (ie, Hohman or Free-Return). Once you know the TOF you know what your TOA should be. Once you set that, make some final tweaks to the TEj (and adjust the TOA the same amounts) to minimize dV.