Question IMFD Off Plane Transfer

[n72.75]

I am trying to do an off plant transfer to the moon from an equatorial low earth orbit.

I can change the TEj and TIn until i get the minimal dV but it will take a lot of time and a lot of gesswork.

What I want to know is if there is any method of finding minimal dV eject windows (less then 3.75km/s).

 

[Piper]

I am trying to do an off plant transfer to the moon from an equatorial low earth orbit.

I can change the TEj and TIn until i get the minimal dV but it will take a lot of time and a lot of gesswork.

What I want to know is if there is any method of finding minimal dV eject windows (less then 3.75km/s).

Yes, by not using IMFD . IMHO, I find TransX much better then IMFD for transfers to the moon (even if it isn't as accurate). Essentially, all you have to do (if you are already in orbit), is boost your "prograde velocity" to the amount you want, and then adjust your eject date forward until you intersect with the moon.

A while ago I wrote a tutorial on off-plane transfers with TransX, I suggest giving it a look.

 

[Tommy]

Use IMFD's surface launch mode to launch into a better starting orbit. There's a special mode in Surface Launch for just this purpose. I beleive it's called "Lunar off-plane", and is the same variable that lets you select "course" mode. Launch immediately when the launch heading (Hed) indicated reaches 90 degrees for best results. This minimizes the "offness" of the plane, and lowers Dv. Also, increasing the TOF (difference between Ejection and arrival times - not shown itself so you have to figure it out) until your transfer is closer to a hohman transfer also lowers Dv. Then you can use the "TOF Lock" option to tune your TEj for optimal efficiency. IMFD seems to default to a quicker (less fuel efficient) transfer, and the TOF is unlocked by default.

For a simple Lunar Off-Plane Transfer, IMFD works every bit as well as TransX, provided you know how to use it as well as you do TransX. TransX's abilities only surpass IMFD's for complex multi-stage trajectories such as multiple sling (ie. Cassini type) trajectories.

With either tool, you can vastly shorten the "trial and error" adjustments by doing a little research first. Figure out how long a Hohman transfer to the moon takes, and you'll know what to set your ejection and arrival times for to achieve that style of transfer. Then you only need to adjust the TEj (assuming you launched at the correct time and heading) for maximum efficiency. Simply trying to adjust TEj and TIn and watching the Dv indicated won't get you a hohman transfer, unless you are already orbiting in a good plane, and get lucky (or plan correctly) on choosing the proper TEj.

In essence, to get a low Dv lunar transfer you will need one of three things:
1, You know the optimal TEj
2, You know the optimal TOF, or
3, You get lucky.

 

[EliNaut]

Yes, by not using IMFD . IMHO, I find TransX much better then IMFD for transfers to the moon (even if it isn't as accurate). Essentially, all you have to do (if you are already in orbit), is boost your "prograde velocity" to the amount you want, and then adjust your eject date forward until you intersect with the moon.

A while ago I wrote a tutorial on off-plane transfers with TransX, I suggest giving it a look.

The thing I don't like about TransX is all the fiddling with it that is required to set up a trip. For example, if I wanted to plan a trip to mars, i'd go right ahead and plan an escape trajectory, easy enough, but when I go to the next stage and realise i'm off a bit, I have to fix what I can back in the escape. Now let's say I did the escape as planned. My course is off, and there could be FOUR things wrong with it. I'll be sitting (and I have sat) at my computer for almost a half an hour trying to find a decent trajectory. Its just too much of a hassle for me . Even when planning before takeoff, I'll spend a good 20/30minutes trying to figure out how to get from point A to point B. And I have no way of knowing if the path I chose is the best window available. Don't get me wrong, TransX is indeed a great addon if you can fully understand and use it, and I love the idea of the stages. I've read many tutorials, but many leave me with more questions than I started with(I.e, telling me WHAT to do, not WHY i'm doing it). I'm going to consult the manual one more time to see if I can make heads or tails of it, and I'm hoping I do.