Help about Orbital Slingshot

[AstroThis]

Hi !
Last week I read a thread named : "The Orbital slingshot" made by someone who has a SE in profile picture ! The problem is that I understand how much that technique is cool and economic but, I didn't understand how it works and so on. I tried but I can't because that's in english and that's to much to read for me, in english.
My question is : Can someone explain me the Orbital slingshot in french plz ?

 

[Horus Lupercal]

My question is : Can someone explain me the Orbital slingshot in french plz ?

You're in luck. The resident astronavigational expert Altaïr (and the guy that wrote said article) occasionally speaks french and might be able to help you.

 

[AstroThis]

You're in luck. The resident astronavigational expert Altaïr (and the guy that wrote said article) occasionally speaks french and might be able to help you.

Cool ! I really want to understand that, I think it can help me to reach Mercury and go back to Earth !

 

[TtTOtW]

Cool ! I really want to understand that, I think it can help me to reach Mercury and go back to Earth !

It can in fact do exactly that

 

[Altaïr]

Hi !
Last week I read a thread named : "The Orbital slingshot" made by someone who has a SE in profile picture ! The problem is that I understand how much that technique is cool and economic but, I didn't understand how it works and so on. I tried but I can't because that's in english and that's to much to read for me, in english.
My question is : Can someone explain me the Orbital slingshot in french plz ?

You're lucky that the author is french

However that's a really long text, I can't translate everything. Maybe you can try with google translate?
The reason why it works is because when you make a fly-by (of Venus for example), the planet is moving in the same time, and transfers some of its movement to the ship. The same way as a ball bounces stronger when it hits a moving truck (see the animations I made in the first post).

More generally, it's possible to chain several gravity assists to save a maximum of fuel. That's what I do to go to Mercury for example. The first step is to aim for Venus, and to make a fly-by. Then, when exiting Venus, you'll be on a transfer trajectory to Mercury the same as if you started from Venus and burnt to Mercury. This already saves fuel because you'll get a slower encounter with Mercury. Then it's possible to chain several fly-bys of Mercury, but this is harder, and the procedure I gave doesn't work anymore as the distances have evolved since 1.4.

I'll show you how to do it with Venus, just give me a moment please.
I tried to make it short to reduce your pain, but I'll explain in french if needed

 

[AstroThis]

Okay thanks !
I think I understand, do you know a video that show (french or english) an example ?

 

[AstroThis]

Okay thanks !
I think I understand, do you know a video that show (french or english) an example ?

Sorry, I reread it and see that your are making an example. I can fait for it with no problem ! I'm doing my Moon Tour

 

[Altaïr]

Ok, here is a small tutorial to use a gravity assist with Venus to go to Mercury.

First, send your ship on LEO, then aim for Venus. Here is my predicted burn:


You can notice that my trajectory goes quite below Venus level at its periapsis. This is intentional, and this is important for what will follow. If you use a cheaper transfer, the gravity assist that will follow won't be powerful enough.

After I performed my burn, my trajectory is the following:


I planned a low fly-by above Venus. Which is important here is to pass in front of the planet. Making the fly-by on the other side would make you go higher on the contrary (which can be used in a different technique to go to Jupiter and above).

Here is my ship before the encounter:

That way, Venus deflects my trajectory backwards, which is what I need here.

Once I entered Venus' SOI, I can see my exit trajectory:

Voila, I'm on my way to Mercury
You can eventually tweak the height of your fly-by to adjust your trajectory. The periapsis of your Sun orbit should be as close to Mercury as possible (ideally, just slightly below). This is to minimize the cost of your insertion burn.

Now here comes the tedious part, I have to wait for a cheap encounter. Aim for Mercury, and wait for the game to propose you a cheap burn. Try to spend less than 50 m/s, and if possible favor a retrograde burn.
I had to spend 45 m/s for this:


Now I have my encounter with Mercury, I can perform my injection, and it's over:


I made a quick calculation, it allowed me to save around 600m/s (by taking into account the burn to get the encounter). This is quite an interesting discount compared to the 2784 m/s you need with a direct transfer. I know you're not really into numbers, but that gives you an idea about what you gain

Of course, you can do something similar when returning from Mercury: aim for Venus, and a new gravity assist will send you directly towards Earth.

Last advice, don't forget to make a quicksave because it's easy to mess a gravity assist at first.

 

[AstroThis]

Ok, here is a small tutorial to use a gravity assist with Venus to go to Mercury.

First, send your ship on LEO, then aim for Venus. Here is my predicted burn:
View attachment 41876

You can notice that my trajectory goes quite below Venus level at its periapsis. This is intentional, and this is important for what will follow. If you use a cheaper transfer, the gravity assist that will follow won't be powerful enough.

After I performed my burn, my trajectory is the following:
View attachment 41867 View attachment 41868

I planned a low fly-by above Venus. Which is important here is to pass in front of the planet. Making the fly-by on the other side would make you go higher on the contrary (which can be used in a different technique to go to Jupiter and above).

Here is my ship before the encounter:
View attachment 41869
That way, Venus deflects my trajectory backwards, which is what I need here.

Once I entered Venus' SOI, I can see my exit trajectory:
View attachment 41870
Voila, I'm on my way to Mercury
You can eventually tweak the height of your fly-by to adjust your trajectory. The periapsis of your Sun orbit should be as close to Mercury as possible (ideally, just slightly below). This is to minimize the cost of your insertion burn.

Now here comes the tedious part, I have to wait for a cheap encounter. Aim for Mercury, and wait for the game to propose you a cheap burn. Try to spend less than 50 m/s, and if possible favor a retrograde burn.
I had to spend 45 m/s for this:
View attachment 41873

Now I have my encounter with Mercury, I can perform my injection, and it's over:
View attachment 41874 View attachment 41875

I made a quick calculation, it allowed me to save around 600m/s (by taking into account the burn to get the encounter). This is quite an interesting discount compared to the 2784 m/s you need with a direct transfer. I know you're not really into numbers, but that gives you an idea about what you gain

Of course, you can do something similar when returning from Mercury: aim for Venus, and a new gravity assist will send you directly towards Earth.

Last advice, don't forget to make a quicksave because it's easy to mess a gravity assist at first.

Thanks !
I'm really tired this evening, bad days in my life.
I'll re-read this with a better attention tomorrow to be sure I understand all the informations !

 

[Altaïr]

No problem, feel free to ask

 

[AstroThis]

No problem, feel free to ask

I reread your text and I understand the Orbital slingshot ! I have to try this today