Flight Question Calculating the Moon's Time to Node

[Will]

Hi,

I am learning how to do off-plane Earth to Moon transfers (using TransX) and can't find out how to accurately find the Moon's time to node (so I can launch about 3 days before it gets there). I know you can approximate it by just looking at the orbit and launching when the Moon is so many degrees from the node but this doesn't seem very 'NASA', I would prefer it if there is some way to display the time.

Thanks,

Will

 

[sorindafabico]

Roughly speaking, you can use the Moon's Mean Longitude value to guess it. Since the variation of the mean longitude is constant* you can easily find the time when the mean longitude equals the longitude of the desired node.

* (360 degrees)/(orbital period)

Edit: sorry, now I read your post properly and my answer is exactly what you don't want. Anyway, it shouldn't be difficult to make a MFD for this.

 

[Will]

How do people on the forum do it? Just by eye?

 

[sorindafabico]

When I want low error i use the Lunar Transfer MFD (LTMFD). I don't know if this is the 'NASA' way you were asking, but to me is the optimal way to travel in Earth-Moon system.

 

[boogabooga]

Off-plane transfers can still be done when the moon is not at its node.

I've never found arriving at a lunar node crossing to be particularly important, except perhaps for free-return trajectories.