Advanced techniques: the gravitational slingshot

[Azuraaa]

VEEGA thats useless for me i have no dlcs

 

[Altaïr]

VEEGA thats useless for me i have no dlcs

Thanks for letting us now, that's some very important information.

 

[Pink]

And it's still super useful in non-DLC game for going to Mercury or doing lots of flybys!

 

[James Brown]

VEEGA thats useless for me i have no dlcs

Well VEEGA is useless but gravity assist of Venus is useful

 

[Azuraaa]

And it's still super useful in non-DLC game for going to Mercury or doing lots of flybys!

When Will i ever use that

 

[Marmilo]

When Will i ever use that

What point are you trying to prove here? You not wanting to use some information doesn't make it useless.

 

[The epic chicken]

When Will i ever use that

When you go to Mercury

 

[Azuraaa]

When you go to Mercury

Ok then

 

[Marmilo]

When Will i ever use that

Team hawk, in mission "under pressure"

 

[Azuraaa]

Team hawk, in mission "under pressure"

Can we just stop this agrument

 

[Marmilo]

Can we just stop this argument

Ok

 

[Space_geek25]

I made a quick calculation of the most interesting resonant ratio. I didn't test them in practice, but this should allow you to plan the second Earth encounter. Here they are:

2:1 : great-axis = 23677.89 Mm
3:1 : great-axis = 31048.42 Mm
5:2 : great-axis = 27486.92 Mm

----

How did you calculate resonant ratio?

 

[Altaïr]

How did you calculate resonant ratio?

It's simple. Let's say you have:
D1 = semi-great-axis of object 1
D2 = semi-great-axis of object 2
n1 = number of turns performed by object 1
n2 = number of turns performed by object 2 in the same time

Then you have (n1/n2)² = (D2/D1)³

For example, to calculate a 2:1 ratio with Earth:
D2 = D(Earth) = 7480000 km (from the planet file)
n1 = n(ship) = 1
n2 = 2

The ship performs one revolution while Earth turns twice.

Then you can deduce:
D1 = D(ship) = D2 × (n2/n1)^(2/3)

So here:
D1 = 11873759.87 km

That's the semi-great-axis. The great axis is twice this value: 23747519.74 km.

This is slightly more than the value I gave above. The reason why is because in the formula, periapsis and apoapsis (which sum equals the semi great axis) are measured from the center of the Sun. But ingame, they are measured from the surface of the Sun, so we have to substract the Sun diameter to get a value we can use ingame.

The Sun radius is 34817 km, so the diameter is 69634 km.

If we substract that value, we get 23677885.74 km, which corresponds to the value above.

You can use that value directly ingame, by taking into account the values given by the game.

Don't hesitate to ask if you need more precisions.

 

[Space_geek25]

It's simple. Let's say you have:
D1 = semi-great-axis of object 1
D2 = semi-great-axis of object 2
n1 = number of turns performed by object 1
n2 = number of turns performed by object 2 in the same time

Then you have (n1/n2)² = (D2/D1)³

For example, to calculate a 2:1 ratio with Earth:
D2 = D(Earth) = 7480000 km (from the planet file)
n1 = n(ship) = 1
n2 = 2

The ship performs one revolution while Earth turns twice.

Then you can deduce:
D1 = D(ship) = D2 × (n2/n1)^(2/3)

So here:
D1 = 11873759.87 km

That's the semi-great-axis. The great axis is twice this value: 23747519.74 km.

This is slightly more than the value I gave above. The reason why is because in the formula, periapsis and apoapsis (which sum equals the semi great axis) are measured from the center of the Sun. But ingame, they are measured from the surface of the Sun, so we have to substract the Sun diameter to get a value we can use ingame.

The Sun radius is 34817 km, so the diameter is 69634 km.

If we substract that value, we get 23677885.74 km, which corresponds to the value above.

You can use that value directly ingame, by taking into account the values given by the game.

Don't hesitate to ask if you need more precisions.

Thank you. I'm trying to complete the mercury Landing, I start with a gravity assist with Venus but I don't know what to do after.

 

[Pink]

Thank you. I'm trying to complete the mercury Landing, I start with a gravity assist with Venus but I don't know what to do after.

A bit general, perhaps you should look at this post of Altaïr's guide in this thread.

Eliptical orbits change things a bit, but here is a similar question, perhaps reading the explanations will enlighten you, or help you figure out a more precise question to ask.
Under pressure mission (I need help)

 

[Idkgeek]

In this last chapter, I'll show you a gravity assist combination that allows to reach Jupiter more efficiently than via a direct transfer. This combination is known as the VEEGA path ("Venus Earth Earth Gravity Assist"), and had been used in real life by the Galileo probe.

For this, I'll use this ship below, parked in LEO at the beginning of the mission:
View attachment 9413
It looks quite small but bulky for such a mission right? If you try to reach Jupiter with a direct transfer burn, this is what you will end up with:
View attachment 9414
The mission will fail.

We will now try this technique out:

The VEEGA path

Level: TRICKY

So for this technique, our first target is Venus:
View attachment 9415 View attachment 9416

As for the previous trip to Mercury, I didn't burn in the transfer window, but after it. As you can see I burnt after the transfer window. This is very important, otherwise you will not be able to raise your orbit later on.

This time, aim for a prograde fly-by, with your periapse close to the atmosphere line.
Then when you enter Venus' SOI, set the Earth as a target, and adjust your trajectory so that you encounter Earth again:
View attachment 9417
You may be able to do this by only adjusting the periapse.

Ideally, your periapse above Earth should be around 250 km. Then time-warp until you enter the Earth's SOI:
View attachment 9418
Now, you must adjust your perihelion so that your "perihelion + aphelion" value is equal to 10959.6 Mm. This generally happens when your aphelion is around 8335 Mm, so you can first aim for that, and then make the necessary adjustments.
If you do not match the exact value, you may have to perform a small correction later. This is affordable, but obviously, it's better to be as close as possible.

This value is important because it ensures that you'll meet Earth again after 2 laps. The closest approach line mechanism won't anticipate that, so it's better to rely on a pre-calculated value.

After 2 turns you encounter Earth again:
View attachment 9419
Ideally, before entering the Earth's SOI, you should adjust your periapse so that it's around 600 km.
Now, the objective is to set the aphelion of your exiting trajectory at 16200 Mm.

OK, now we are on a transfer trajectory to Jupiter. When you reach the aphelion, burn prograde to raise your perihelion to 3000 Mm. This will ensure you won't meet Earth again (you still have to watch out for Mars though), and you'll get slightly closer to Jupiter every 2 turns, until you get an encounter:
View attachment 9420 View attachment 9421 View attachment 9422
Now compare this with the fuel consumed on a direct transfer burn, you'll immediately notice the impressive amounts of fuel saved.

In case you get an encounter with Mars in the process, you may just slightly modify your trajectory to avoid it (if you do it early enough this will cost practically nothing), and come back to your initial trajectory after one turn, once the "danger" has passed.

This trajectory will save around 400-500 m/s, which is quite valuable with a heavy ship.

With the 1.5 navigation system where would I start the first burn because I have tried several times by just looking at what you had done and I just can't get an earth encounter. Even with different distances after ideal encounter.

 

[Catalyst_Kh]

If you don't use mods, which immediately show resonate orbits on map screen, then you would have to calculate resonate orbits in excel by yourself, or some other way, excel is not necessary. So, when you are exiting Venus's SOI you need to aim for specific sum of apohelion and perihelion numbers to get such orbit. Also, you can adjust your orbit later, it doesn't have to be done near Venus.

It is easier when you are exiting Earth after first gravity assist from Earth - you just need to catch it in 2-3-4 laps or in 1.5-2.5-3.5 laps, right from here. But to get to Earth first time after you only exited Venus - that needs some bearings. It might be done in different ways, which is easier for you. For example, i did it that way - i exited Venus and simply timewarped to point, where i intersect with Earth orbit, then i switched off time warp when my ship was intersecting and analyzed how much angle degrees Earth is now from this point (where my ship is), so i could pick a resonate orbit with correct ratio of resonance, then i put this number to excel and get exact perihelion and apohelion values from the formula, so i could adjust my orbit and timewarp to the point where i will meet Earth. Thus i never even looked at Earth position in advance - i only looked at Venus position, so i could get to it easily from Earth orbit.

Or you can simply make one or several laps after you exited Venus and look for any close proximity with Earth, then you load your quicksave near Venus and increase or decrease your velocity a little, or changing your vector of exiting Venus's SOI a little, so you would repeat your path, but catched up Earth this time in that point where you was close previously.

If second time you still missed - you can visually evaluate by how much more you need to change your speed or your exit vector and reload again. Thus without any calculations of numbers you will catch Earth for the first gravity assist. The same could be done even for second rendezvous with Earth too. But entering simple formula in excel was simply easier for me.

 

[Altaïr]

With the 1.5 navigation system where would I start the first burn because I have tried several times by just looking at what you had done and I just can't get an earth encounter. Even with different distances after ideal encounter.

You must not aim for a perfect encounter, because otherwise you won't be able to use Venus to raise your orbit. You must wait past the perfect transfer, so that your perihelion goes below Venus level:


Then by leaving Venus with your new apohelion slighty below Mars level, you can encounter Earth again:


I must say it's not easy with the 1.5 navigation system. If you play on PC, the closest approach line mod will help you greatly.
No, I'm not doing advertising

 

[Idkgeek]

You must not aim for a perfect encounter, because otherwise you won't be able to use Venus to raise your orbit. You must wait past the perfect transfer, so that your perihelion goes below Venus level:
View attachment 99158

Then by leaving Venus with your new apohelion slighty below Mars level, you can encounter Earth again:
View attachment 99159

I must say it's not easy with the 1.5 navigation system. If you play on PC, the closest approach line mod will help you greatly.
No, I'm not doing advertising

I did try that but somehow it didn't workI mostly play on mobile but I'm gonna have to whip out my laptop for that one! Use it now before it gets broken by ksp2!

 

[Catalyst_Kh]

Show a video of how you are doing it, then it will be clear what is wrong and how to fix it.

 

[Idkgeek]

I decided to just do it brute force by getting as much delta v as possible from the Venus encounter and then timewarp until I got an encounter with earth, tweaked encounter to make the most of it, perfom a burn at oeriapsis to take advantage of the oberth effect and then timewarped into Jupiter. In fairness it was more of a VVVEGA as I encountered Venus a few more times whilst timewarping to Earth. As you can see I landed on a jovian moon with a much smaller rocket. Do you have any good challenge ideas? I have completed everything in team hawk and completed a few of the challenge in the forum and now I am bored!

 

[Catalyst_Kh]

I have some challenge ideas, i wanted to summarize it all in one topic. But still delaying making that.
You can start with a challenge of finding the most cheapest way to reach Jupiter. There are some ideas, which might improve above VEEGA a little, but i didn't tested all of them yet. By cheapest i mean lowest ΔV requirements to get from LEO to Jupiter, at a cost of extra "game years" if needed.

 

[Azuraaa]

VEEGA thats useless for me i have no dlcs

Well That aged like milk