Moon to Earth.. two trips, different trajectories why?

[caningo]

Alright guys, this post is for all you experienced orbiteers out there. If you guys could lend a hand to this rookie I would really appreciate it.

I am doing the IMFD tutorial Moon2Earth located @ http://koti.mbnet.fi/jarmonik/Moon2Earth.zip. So I follow the each step until i complete orbit eject and on my way to earth, but something weird happens... see for urself:



As you can see I am doing this flight with a DGIV. My question is, why is the trajectory line so bent? As I progress the flight, the ship doesn't move hardly at all and finally starts moving away from the moon once it is out of it's SOI.

I found this really weird because when I was flying AMSO this never happened when I did the TEI burn. See the picture for AMSO below:



So I am totally confused. Why doesn't my DGIV trajectory look like the one for AMSO? Aren't they basically the same thing? Trying to reach earth? :huh:

I hope I've been clear enough.

CANINGO eace:

 

[Scarecrow]

Well I'm no IMFD expert (I'm a TransX addict), but perhaps the fact that the DGIV IMFD screenshot showed IMFD in "ReEntry Display" mode and the AMSO IMFD screenshot showed IMFD in "Pe 1 of 2" mode has something to do with it?

I have no idea what I just said, but perhaps it can give you a clue . I agree, that trajectory looks rather strange.

 

[Urwumpe]

You launched into different trajectories from different orbits. The first one, was in a prograde orbit, while Apollo was in a retrograde orbit.

 

[caningo]

Well I'm no IMFD expert (I'm a TransX addict), but perhaps the fact that the DGIV IMFD screenshot showed IMFD in "ReEntry Display" mode and the AMSO IMFD screenshot showed IMFD in "Pe 1 of 2" mode has something to do with it?

I have no idea what I just said, but perhaps it can give you a clue . I agree, that trajectory looks rather strange.

Hey scarecrow. I tried switching between views and still get the same trajectory. Thanks for the feedback and quick reply.

You launched into different trajectories from different orbits. The first one, was in a prograde orbit, while Apollo was in a retrograde orbit.

Urwumpe. My question for you then is... does launching into a retrograde orbit reduce flight time in the first case? And if so... where in IMFD can I change between prograde and retrograde? :hmm:

Caningo

 

[Urwumpe]

Urwumpe. My question for you then is... does launching into a retrograde orbit reduce flight time in the first case? And if so... where in IMFD can I change between prograde and retrograde? :hmm:

It does not directly affect your flight time. The L-shaped trajectory you see in one, comes from the fact that you needed to leave moon with only minimal excess energy, causing you to loiter a long time at the border of moons gravity field. The second trajectory had more excess velocity.

The first one could have looked like the second, if you had chosen the right eject position - ejecting earlier.

There are many way to get to Earth, and many ways to leave moon to get on the chosen course to Earth.

 

[caningo]

The first one could have looked like the second, if you had chosen the right eject position - ejecting earlier.

So how do I do this? Does my oV have to be bigger than a certain quantity? And how do I choose the right position? I really don't like lingering in the moon's gravity field that long...

Caningo

 

[Urwumpe]

So how do I do this? Does my oV have to be bigger than a certain quantity? And how do I choose the right position? I really don't like lingering in the moon's gravity field that long...

When planning the eject burn from moon, you need to just plan to enter a transfer orbit, which has it's apogee well above the moon. This will require IMFD to make you leave moon on a hyperbolic orbit with lot's of excess velocity.

 

[caningo]

When planning the eject burn from moon, you need to just plan to enter a transfer orbit, which has it's apogee well above the moon. This will require IMFD to make you leave moon on a hyperbolic orbit with lot's of excess velocity.

OK I'm still kinda confused. Let's see. Until now I have been using orbit eject with the burn vector information provided by planet approach program. From what you are saying I guess I can't use that info and have to use my own data correct?

Assume I takeoff from Brighton Beach and establish an altitude of 100km above lunar surface (that being my apogee). Say I go to orbit eject program and select either lower-orbit eject or higher orbit eject mode. Do I have to adjust my oV to have that excess velocity?

Could you walk me through the initial steps if you can... cuz I really have no clue what I am doing. :lol::rofl:I understand the logic, but I don't know how to implement it in IMFD.

Thanks!

 

[ar81]

Want to know about IMFD?
[ame="http://www.orbithangar.com/searchid.php?ID=3403"]Tutorial: Concepts for Interplanetary MFD 4.2.1[/ame]

 

[toodoo213]

I believe its that there are different sources in each one. The first one is Moon, and the second one is the Sun. As you leave Moon's SOI the approach to Earth deteriates because IMFD still thinks your orbiting the moon. Same thing happens in with Interplanetary travel. If you notice in a simple Earth 2 mars trajectory, if you set the source to Earth, it seems like your swirling towards the sun and the orbit seems strange. Same with first shot. I'll test this theory later, but i believe thats it.