Team Hawk submission - Mercury mission

Mooncrasher

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#2
Do you have an youtube video or series of screenshots? DropMe does not appear to be allowing me to download the video....
 

Mooncrasher

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Badge granted, well done. :)
Small note, if you were to encounter Mercury on the other side of its orbit, where it's closer to the sun, you can get captured whilst using a lot less fuel.
 

Catalyst_Kh

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But to reach that place i would have to meet Venus from opposite side of it's orbit too, and then i would have to burn more fuel near Venus to get to that lower part of Mercury's orbit. Wouldn't that burn of more fuel near Venus just negate the benefit of capturing Mercury's orbit cheaper?
 

Mooncrasher

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#6
You should be burning a minimal amount of fuel near Venus, so it's not a worry. ;)
 

Catalyst_Kh

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You should be burning a minimal amount of fuel near Venus, so it's not a worry. ;)
Please show a way how with minimal amount of burn near Venus it is possible to reach Mercury's perihelion.

I didn't found such way. I tried different vectors to meet Venus in the first place, but even best vectors gives me perihelion of near Mercury's aphelion level, but since this level is not reachable anymore (as i met Venus from Merucy's apohelion side already) - i have to burn a lot of fuel near Venus to get to Mercury's perihelion.

Should i use Venus 2-3 times, before i go to Mercury? Or there is a better way to accomplish it with minimal amount of fuel burned?
 

Catalyst_Kh

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I replayed that mission (link) from a quicksave, when i only first time approaching Venus. If i change my trajectory near Venus just a little, i can catch Venus again over 4 laps around the sun in the same place and i can take one more deceleration from it, but that would be final, since my vector will be parallel to Venus after second rendezvous, and that means at any next lap i can't get more deceleration, i can only accelerate from it.

That second meeting conciderable reduced amount of fuel needed to burn to get to Mercury's perihelion. But it is still much cheaper to get to Mercury's apohelion - it requires almost no burn at all - if we just meet Venus from the other side of it's orbit (around the sun) in the first place.

And from Mercury's apohelion we can shift our orbit around the sun to Mercury's orbit around the sun by encounters with Mercury itself. Then we will have the same orbits and thus I cant find any difference at what point we approached Mercury first time.

So, i don't understand - how this benefit works? What do i get for extra fuel burned near Venus? It seems like just wasted fuel. Please tell correct strategy with it.
 

Mooncrasher

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#9
Mercury mission
Here's Altaïr 's mercury submission, it demonstrates how he did a flypast of venus when it was on the "left" of the screen, which meant that the gravity assist from it "caught" mercury on the "right" of the screen, where it is closer to the sun due to eccentricity of its orbit, and thus moving faster. That already gives a huge benefit, since he encounters Mercury with around 1500 m/s of relative velocity (an approximate guess, since the relevant picture was from the edge of the SOI, not near mercury), instead of over 2100 m/s like you did. That's 600 m/s of dV that you can potentially save by letting gravity do more work for you, it's a lot!
You don't need to chain gravity assists like he did to maximise the benefit, simply catching planets near the periapsis when you're going "inwards" into a gravity well and near the apoapsis when you're going "outwards" out of a gravity well can save a lot of fuel if the orbits are significantly eccentric.
 

Catalyst_Kh

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I see there that Altaїr didn't get a lot of slowing down from first rendezvous with Venus and instead used first rendezvous to gain even more difference in vectors with Venus, so at his next rendezvous he would get much more deceleration from Venus, than he could get with "normal" vector of first approach. And that would finally reach Mercury's perihelion without burning too much fuel.

That is very clever solution, it did not come to my mind. Thank you very much Mooncrasher!
 

Mooncrasher

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#11
Yes, I overlooked that two passes of Venus are required in this case.:eek:
 

Altaïr

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I replayed that mission (link) from a quicksave, when i only first time approaching Venus. If i change my trajectory near Venus just a little, i can catch Venus again over 4 laps around the sun in the same place and i can take one more deceleration from it, but that would be final, since my vector will be parallel to Venus after second rendezvous, and that means at any next lap i can't get more deceleration, i can only accelerate from it.

That second meeting conciderable reduced amount of fuel needed to burn to get to Mercury's perihelion. But it is still much cheaper to get to Mercury's apohelion - it requires almost no burn at all - if we just meet Venus from the other side of it's orbit (around the sun) in the first place.

And from Mercury's apohelion we can shift our orbit around the sun to Mercury's orbit around the sun by encounters with Mercury itself. Then we will have the same orbits and thus I cant find any difference at what point we approached Mercury first time.

So, i don't understand - how this benefit works? What do i get for extra fuel burned near Venus? It seems like just wasted fuel. Please tell correct strategy with it.
It's cheaper to aim for Mercury apohelion, but then you have to look at what it costs to get captured in Mercury orbit.

If you aim for Mercury's apohelion, you'll find yourself in this situation:
Spaceflight Simulator_2023-02-20-08-12-41.jpg

Your perihelion is at Mercury's apohelion, but your apohelion is at Venus level (Venus orbit is circular). Now you have to lower your apohelion to Mercury's perihelion, and that strategy maximized the difference between them, because the eccentricity doesn't play in your favor now.

On the contrary, if you aim for Mercury's perihelion:
Spaceflight Simulator_2023-02-20-08-08-45.jpg

That configuration costed more, but you're now in a more favorable situation: you have to reduce your apohelion from Venus level to Mercury's apohelion, the difference is much lower.

So all in all, you tend to lose on one side what you gain on the other side. So why is it more efficient to aim for Mercury's perihelion then? In fact, mostly because Venus is more massive than Mercury. The fact that Venus is massive allows to perform some very efficient gravity assists. If you use this to your advantage, it'd better be for the most expensive part of the trip, since that's the part you will make free. On the contrary, Mercury is light, which means that chaining gravity assists with it is less efficient (but it still works), and you'll have less Oberth effect from Mercury. It means that your insertion burn would quickly be more expensive. So all in all, it's better to reach Mercury in the most favorable configuration since this is where you could spend a lot.

I see there that Altaїr didn't get a lot of slowing down from first rendezvous with Venus and instead used first rendezvous to gain even more difference in vectors with Venus, so at his next rendezvous he would get much more deceleration from Venus, than he could get with "normal" vector of first approach. And that would finally reach Mercury's perihelion without burning too much fuel.

That is very clever solution, it did not come to my mind. Thank you very much Mooncrasher!
That's exactly that. The first gravity assist is not that powerful, but the purpose is to chain a second gravity assist so I aim for a resonant orbit. Then the second one is performed at full power. All in all, that gives a better deflection than a single slingshot at full power.

In theory, it's possible to achieve the desired deflection in a single gravity assist, but that would imply to pass through the planet, and I'm afraid that the probe is not designed for that. :)
 

Catalyst_Kh

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#13
I also want to try simplified way - just to burn a little more fuel right at LEO to get more difference in vectors with first approach to Venus (because of making much lower perihelion for our ship). Then with extra speed and extra angle difference in vectors we might end up on hoffman trajectory fo Mercury's perihelion directly after the single rendezvous with Venus. And it might cost only a little more burning near Earth in the first place. Or maybe not so little, that is only a test can reveal. :)

In this simplified way it is much easier to aim for exact Venus position at X radial degrees "before" Mercury's apohelion, so after first GA from Venus we could "spend some time" with Venus, while it is traveling for those X degrees, and then we espace Venus's SOI right above Mercury's apohelion, so we would transfer directly to Mercury's perihelion without more burning at all - everything was "burned in advance" in LEO already.

Thus we can catch Mercury at the very best position and not somewhere shifted to the side, because it was hard to predict where would be second exit point from Venus's SOI after second rendezvous with Venus.
 
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