How can I make a slingshot around Earth ?

[Thierry Lys]

I have already done a complex travel with slingshots, taking-off from Earth, doing a slingshot around Jupiter and another one around Saturn to go to Titan. I used TransX (basic version) for that.

But i can't realise my new project. I want to go to Jupiter, taking-off from Moon (Brighton beach), and doing a slingshot around Earth (with of course an add of deltaV).
I know that i have to swich off the autoplan and to choose the appropriate plan. First of all it is difficult for me to built a correct serie of stages corresponding to my project.
But the main problem occures when i want to plan the burns and the corrections. Normaly when i'm planing a correction in a stage, i can see the planed new orbit in the folllowing stage which anable me to prepare all to encounter the planet or to get the good position for the slingshot. But here i can't. For example i'm orbiting Moon, i can see what a burn would do in the stage centred on Moon but not in the following stage centred on Earth. So i can't know when to do my burn : i can't plan anything.

I know that TransX has limitations for complex flights with slingshots, but if it is possible to do what i wan't, any explaination, clarification or advise would be welcomed.

 

[n72.75]

The problem that i think your running into is that both transx and IMFD tend to want to slingshot only planet to planet of moon to moon(orbiting the same planet)

A workarount is to just let the sun be the reference during the slingshot.

capeesh?

If not there is many people who can explane it better.

-n72

 

[Thierry Lys]

I agree and between the stage centred on Earth and the stage centred on Jupiter i put a stage centred on the Sun. It is like a traditionnal slingshot around a planet to go to another planet. But i want to plan my burn and the slingshot when i'm still on Moon, because if don't do that i can't know when i need to take-off. So i need information about Jupiter from the Moon.

These are the stages i have planned (central body) : Moon -> Earth -> Sun -> Jupiter. When i'm on a stage planning a manoeuvre, i can't see the consequences on the following stages. What you have normaly, and what you need absolutely.
I also tried this : Moon -> Earth -> Sun -> Earth -> Sun -> Jupiter but it was totaly innefficient.

In fact, i want to know when to do TEI from Moon to be able to point to Jupiter after another burn near Earth.

 

[agentgonzo]

Flytandem has done some interesting slings around the Earth starting from the moon. A simple search of the forum for "TransX Flytandem surrogate" should yield some good results (he was using a surrogate ship in orbit around the Earth for it).

Hope that helps.

 

[Kveldulf]

Also, if you download the Complete IMFD manual from O-H, there is a link for a trip from the Moon to Mars, using a slingshot around Earth.

 

[Thierry Lys]

I worked hard yesterday to find a solution, and i finally found a plan that would be able to work. The adresses you've shawn me were really helpful. Congratulations for the Complete IMFD Manual, it is great work.

To go from Moon to Jupiter, using TransX, 4 stages are needed. They are respectively centred around :
Moon : traditional escape plan around the body you've taken-off from.
Earth : autoplan off but don't plan anything.
Sun : traditional sling direct plan (autoplan still off).
Jupiter : normal encounter plan.

The major problem i was facing is that i couldn't put a stage of encounter with Earth directly after the stage centred on Moon. So I couldn't plan the sling in the traditional way. I needed 2 pieces of informations and i finally found how to get them :
Date of the whole departure (as a trip from Moon to Earth only takes 4 days you can consider the date of the daparture from the Moon as the date of the sling around Earth. If there is a imprecision, a tiny correction after the slingshot burn would be able to fix the problem) : on the sling direct plan (3rd one) you can enter the parameter of the slingshot even if you are still on the Moon. Therefore you are able to know when to take off.
Parameters of the burn (to add velocity) : when you taken off from Moon going on an orbit which leads you to Earth (normal trip from Moon to Earth) you can plan a manoeuvre in the 2nd stage (centred on Earth). Just wait until you have left the gravity influence sphere of the Moon. You enter parameters of the manoeuvre and you can see in the following stage (centred on Sun) your new prevised orbit (in green). You are then able to plan a burn which leads you to Jupiter.

I will test it during the following week but i'm sure that i can do all what i said. However i may face other problem during the mission. Another difficulty is that for the manoeuvre (in fact the slingshot burn) you have to pass by a precise point near Earth and this can depend on your sense of rotation around Earth. So when you have an idea of where you have to pass to do the add-velocity burn, you should have to make another correction to pass by this precise point. However it don't have to be really precise as any correction after the leaving of Earth gravity influence sphere would fix the imprecisions (but this may not work for a trip from Europa to Io with a sling around Jupiter).

I think this can work but if anyone realise that i made mistakes, or can improve the procedure just tell me. I think if this work i would be able to be on an orbit which pass near Jupiter with still half of the fuel, which anable to do great trip with limited fuel.