Direct Insertion to Moon via IMFD

[Arrowstar]

Hello all. I've been tinkering with IMFD lately and thus far have been reasonably pleased. However, I can't seem to setup anything other than free-return trajectories for my Earth-moon flights. I'm specifically looking to setup a trajectory that'll put me directly in lunar orbit. Can someone either explain how to set this up or point me in the direction of documentation that does? I've been over the web, but can't seem to find anything.

Thanks for the help!

 

[tblaxland]

If you can do a free return then you can get into lunar orbit. You will always need to do an insertion burn at the moon because the trajectory that gets you from Earth to the Moon will have a hyperbolic trajectory with respect to the Moon.

The rough and ready way to do lunar orbit insertion (LOI) is to simply point your craft retrograde and light the main engines when you are at or near lunar periapsis. For a more accurate solution you can use IMFD's orbit insertion program or BurnTimeCalcMFD.

 

[Arrowstar]

Right, I understand the method behind the free return trajectory and insertion. So there's no way to directly burn right into Lunar orbit? In that case, how should I setup my TLI burn so that when I get to the moon, I only have to use the minimum amount of fuel to get into lunar orbit? That is, use a high periapsis, a low periapsis, any inclinations?

 

[Zatnikitelman]

No, there are no tutorials currently for doing much with IMFD outside of just follow this and it works. But nothing explains what to do with other situations. I've been trying to dig up some help or atleast a semi-useful tutorial for months now. You're not the only one who's frustrated with IMFD.

 

[to be]

Low Periapsis, and inclination doesn't matter, so whatever is most efficient to get there. I can't think of any way it would ever be possible to go from LEO to Lunar orbit, without an insertion burn, barring starting in an orbit very close to the moon's, and having the sun or earth, or some other body happen to pull you into lunar orbit. To do this would be massively wasteful of fuel, so it is best to just do an insertion.

 

[Linguofreak]

So there's no way to directly burn right into Lunar orbit?

Not really. Basically, you start out far from the moon, and as you fall towards it, you pick up speed due to the moon's gravity. If something doesn't happen to slow you down when you get there (making a burn, hitting the moon, etc.), you'll just go flying on by and all that speed will carry you right back out.

Basically any time you need to change your speed or direction, you need to perform a burn. There are a few ways to get around this; you can aerobrake, lithobrake, or do a gravitational slingshot, but the moon doesn't have an atmosphere, so you can't aerobrake, and it doesn't have any moons of it's own, so you can't slow yourself down with a slingshot. All that's left is lithobraking. I tend to avoid lithobraking, and real astronauts *really* try to avoid it. It is left as an exercize for the reader to find out why.

So that just leaves a plain old fashioned burn as the only way to enter lunar orbit.