Altaïr's crazy stuff

[Astro826]

Now you have to teach me

Start off with a double lunar assist that kicks you out of Earths SOI. This has to be timed so it is close to a prograde, retrograde, or potentially a completely radial escape, which allows you to mess with orbital resonance(with the radial escape you're aiming for 1:1 resonance which skips the calculations, but it's probably harder to perfect than the other ones). Calculate the ratio of orbital periods you can get with your strongest orbit difference, then find the best resonance you can reach and its corresponding semimajor axis. Go back to before the last assist you did and adjust it so your trajectory has that semimajor axis. Then wait for the next encounter to show up and mess around with adjustments to see if you can get an advantageous moon assist on the flyby. This is when you're passing lunar orbit at an angle and the deflection by the moon pushes that angle closer to lunar prograde. Then: again maximize the assist and calculate the orbital period ratio; go back and adjust the assist so it puts you on an orbit with that ratio. Repeat a lot. If you can't get a decent lunar assist on any given flyby, aim for an orbit that puts you on a 1:1 resonance. This will show up immediately in game with a high orbit line count, speeding up the next encounter a lot. Just adjust your periapsis until you see another flyby trajectory, then you have another chance at a lunar assist. Make sure to use saves liberally for just about ever maneuver, you have no idea when you'll have to go back and do it again.

I used the lunar assists to raise my orbit, it took 6(the first 2 were still in Earth orbit) of them to gain enough relative velocity to do venus gravity assists. Once my apoapsis reached a bit past Mars, I did 2 Earth flybys to change that high orbit into a low one that passed by Venus. I had 7 Earth flybys total.

With ANAIS, you'll probably have a much easier time getting back to another Earth encounter.

 

[Axiom]

Why do you use lunar assists on the flybys rather than earth assists?

 

[Astro826]

Why do you use lunar assists on the flybys rather than earth assists?

Flying past Earth alone does not change the flyby velocity, and more flyby velocity is what we need to reach Venus.

 

[Axiom]

Oh ok, so I assume the crux of this mission profile is using the moon to make the flyby as fast as possible so you can use Earth to reach Venus efficiently

 

[Astro826]

Oh ok, so I assume the crux of this mission profile is using the moon to make the flyby as fast as possible so you can use Earth to reach Venus efficiently

Yes. Getting a trajectory to do Venus assists with takes more delta V than getting to the moon. Many lunar assists can supply all the delta V difference. You can keep flying by the moon with an angle on each Earth flyby, so you can always get an advantageous lunar assist (if the moon is in a place that makes this possible)

 

[Axiom]

Yes. Getting a trajectory to do Venus assists with takes more delta V than getting to the moon. Many lunar assists can supply all the delta V difference. You can keep flying by the moon with an angle on each Earth flyby, so you can always get an advantageous lunar assist (if the moon is in a place that makes this possible)

That makes sense now! Thanks!

 

[ilikespace]

Change your pfp to this

 

[Altaïr]

Change your pfp to this
View attachment 122312

Sorry no, my name was inspired from the star named that way, not the lunar module.

 

[ilikespace]

Sorry no, my name was inspired from the star named that way, not the lunar module.

Oh ok

 

[Marmilo]

Oh ok

Polish confirmed

 

[ilikespace]

Polish confirmed

New favorite signature

 

[Altaïr]

I definitely had to try that technique of chaining lunar assists showed by Astro826
As I expected, this proved to be very painful to grind a little ΔV... But I'm happy to announce that today, I get my throne back

With 32.5% of fuel remaining, I'm left with 1777.3 m/s of ΔV... Which is practically half of the initial ΔV budget of 3597.3 m/s.

My congratulations Astro826, you set the bar very high. I must say that even with ANAIS it was hard to beat. Honestly if I hadn't had the PC version and the mods I would certainly not have had the patience to do this

 

[Dahzito]

I definitely had to try that technique of chaining lunar assists showed by Astro826
As I expected, this proved to be very painful to grind a little ΔV... But I'm happy to announce that today, I get my throne back
View attachment 122420
View attachment 122421
With 32.5% of fuel remaining, I'm left with 1777.3 m/s of ΔV... Which is practically half of the initial ΔV budget of 3597.3 m/s.

My congratulations Astro826, you set the bar very high. I must say that even with ANAIS it was hard to beat. Honestly if I hadn't had the PC version and the mods I would certainly not have had the patience to do this

Wow, I'm super impressed, also because of the use of lunar gravity assists. The space stig now has the throne again!
Will have to see the explanation that Astro826 gave about the technique he used because it looks very interesting!

 

[Altaïr]

Wow, I'm super impressed, also because of the use of lunar gravity assists. The space stig now has the throne again!
Will have to see the explanation that Astro826 gave about the technique he used because it looks very interesting!

Sure. It consists in using the Moon to perform gravity assists. The Moon is not very massive so one fly-by isn't very efficient, but if you cumulate enough you can get a substantial boost on the long term.
The first step is to aim for the Moon instead of Venus, then chain 2 fly-bys:

The first fly-by will send you on a higher orbit, but the second one will eject you from the SOI. The problem is that you won't have enough energy to reach Venus. A possibility would be to simply chain Earth fly-bys, but this alone won't allow you to increase your speed. You would just be ejected from Earth at the same speed at which you entered. The solution is to perform an Earth-Moon gravity assist: the Earth alone won't help you, but the Moon can give you some energy. So on each encounter with Earth, you have to make sure you also make a fly-by of the Moon, like this for example:

Then you just have to chain that maneuver. Astro826 had to do it 8 times. Personally I lost the count but this was something similar. The result is that after each Earth-Moon gravity assist you're ejected on a random trajectory, but it doesn't matter. What matters is that you can synchronize your orbit with Earth so that you can chain encounters:

I chain them with the approach lines, Astro826 calculates a resonant orbit using the third Kepler law. I let you guess which method is easier
You probably imagine what Astro826 went through...

Then once you have chained enough Earth-Moon gravity assists, just use the Earth again to deflect your trajectory and go to Venus:

Then it's business as usual

For the little story, the Earth-Moon gravity assist has never been used for real until now, but the JUICE probe will use it for the first time next month. Apparently they call this "Lunar-Earth Gravity Assist" or "LEGA".

 

[Axiom]

I definitely had to try that technique of chaining lunar assists showed by Astro826
As I expected, this proved to be very painful to grind a little ΔV... But I'm happy to announce that today, I get my throne back
View attachment 122420
View attachment 122421
With 32.5% of fuel remaining, I'm left with 1777.3 m/s of ΔV... Which is practically half of the initial ΔV budget of 3597.3 m/s.

My congratulations Astro826, you set the bar very high. I must say that even with ANAIS it was hard to beat. Honestly if I hadn't had the PC version and the mods I would certainly not have had the patience to do this

All hail the master of gravity!

 

[Mooncrasher]

That's it, we're cutting the amount of fuel in that craft by half, we need to set a higher bar for everyone else.

 

[Astro826]

I definitely had to try that technique of chaining lunar assists showed by Astro826
As I expected, this proved to be very painful to grind a little ΔV... But I'm happy to announce that today, I get my throne back
View attachment 122420
View attachment 122421
With 32.5% of fuel remaining, I'm left with 1777.3 m/s of ΔV... Which is practically half of the initial ΔV budget of 3597.3 m/s.

My congratulations Astro826, you set the bar very high. I must say that even with ANAIS it was hard to beat. Honestly if I hadn't had the PC version and the mods I would certainly not have had the patience to do this

What did your fuel levels look like at key points in the mission? (First moon encounter, first Mercury encounter, Mercury orbit, etc). The only thing I could conceivably improve upon is the Mercury V-leveraging, vanilla is just too limited to get theoretical best maneuvers for all the Earth-Moon flybys. I made sure not to waste a drop of fuel on that leg of the journey, I wonder how human perfect performance compares (and if I can improve my V-leveraging).

 

[Darthan]

The first fly-by will send you on a higher orbit, but the second one will eject you from the SOI. The problem is that you won't have enough energy to reach Venus. A possibility would be to simply chain Earth fly-bys, but this alone won't allow you to increase your speed. You would just be ejected from Earth at the same speed at which you entered.

It is possible to reach Earth escape velocity with a single lunar flyby see probe to Europa. The best I've managed had an apoapsis half way to Mars orbit.

It is possible to raise your orbit using only Earth flybys plus a small apoapsis burn, but is faster with lunar flybys. Not sure about efficiently lowering the orbit with Earth flybys alone, can increase eccentricity though.

 

[Altaïr]

What did your fuel levels look like at key points in the mission? (First moon encounter, first Mercury encounter, Mercury orbit, etc). The only thing I could conceivably improve upon is the Mercury V-leveraging, vanilla is just too limited to get theoretical best maneuvers for all the Earth-Moon flybys. I made sure not to waste a drop of fuel on that leg of the journey, I wonder how human perfect performance compares (and if I can improve my V-leveraging).

Sure. I'll show you the screenshots I have right now, but tell me if you want me to detail a step in particular.

After the Moon transfer, I was left with 70% of fuel, and 2942.7 m/s of ΔV:


This is when I'm about to encounter Venus: 69.8% of fuel, 2936.3 m/s of ΔV:

I didn't realize myself I used that little fuel... I used the approach lines to plan my encounters largely in advance. It occured that I could anticipate an encounter 15 orbits before it happens, and the correction is very very cheap in this case. Especially that I usually use every fly-by opportunity to adjust my trajectory for the next encounter, like here:


Upon the first encounter with Mercury, my fuel has barely dropped:

This is because I usually perform 2 Venus assists. The first one sends me on a resonant orbit of ratio 4:3 (my ship orbits four times when Venus orbits three times), then the second one sends me towards Mercury perihelion.

For the V-leveraging steps I don't have all of them, but I have this one:

60.3% of fuel and 2684.4 m/s remaining at that stage.

Finally, Mercury orbit:

51.9% of fuel, 2444.7 m/s remaining.

I noticed that the remaining fuel there could depend a lot on your ability to aim for an insertion when Mercury is at the perihelion, which is explained by a bigger Oberth effect from the Sun. A first attempt left me with 29% of fuel after landing, because I was less efficient on this point.

Finally, a good landing technique, when you comes to a stop right above the ground so that the powered descent is minimal can make you gain a few tenths of percent point:

This is the corresponding screenshot:

The landing consumed 667.4 m/s of ΔV overall.

 

[Axiom]

According to my calculations the theoretical limit of how much fuel you can have when you land is 40.5%, assuming you only spend delta-v going to the moon and somehow not spend any fuel until you have to get into Mercury SOI and land.
Edit: This assumes a perfect landing aswell

 

[Altaïr]

It is possible to reach Earth escape velocity with a single lunar flyby see probe to Europa. The best I've managed had an apoapsis half way to Mars orbit.

I see. But it's also because you used a more powerful transfer than the simple Hohmann transfer. Strictly speaking, maybe it's possible with a single fly-by assuming a Hohmann transfer, but you'll get more benefit from a second fly-by, you would be ejected from the Earth SOI at a very low speed otherwise.

It is possible to raise your orbit using only Earth flybys plus a small apoapsis burn, but is faster with lunar flybys. Not sure about efficiently lowering the orbit with Earth flybys alone, can increase eccentricity though.

Yes, this is what's called the V-infinity leveraging technique. You can also lower your orbit that way if that's your intention of course. But in this case you have to burn at the perihelion to raise your apohelion instead.

According to my calculations the theoretical limit of how much fuel you can have when you land is 40.5%, assuming you only spend delta-v going to the moon and somehow not spend any fuel until you have to get into Mercury SOI and land.
Edit: This assumes a perfect landing aswell

That leaves me 297 m/s of improvement...
Did you take into account the ΔV used for V-leveraging too? Because you'd have to spend those too, especially that there's no real alternative, apart from a direct insertion of course.

 

[Axiom]

Did you take into account the ΔV used for V-leveraging too? Because you'd have to spend those too, especially that there's no real alternative, apart from a direct insertion of course.

Well no, but that was meant more as an upper bound for the maxiumum performance.
The calculation was done assuming a Hohmann transfer to the moon and just capturing and landing on mercury

 

[floatingfuel]

Just wondering, what if the V leveraging is omitted? Will the ship eventually stuck on a resonant orbit? Or there could be a cheap capture when the ship's apohelion aligns with Mercury's orbit, eventhough the ship's perihelion have descended farther?

 

[Axiom]

Just wondering, what if the V leveraging is omitted? Will the ship eventually stuck on a resonant orbit? Or there could be a cheap capture when the ship's apohelion aligns with Mercury's orbit, eventhough the ship's perihelion have descended farther?

The problem is that regular gravity assists don't change the relative velocity around a celestial body. You have to V-Leverage and spend fule while doing so to land as efficiently as Altaïr and Astro826. My calculation was with it ommitted so the max is probably much lower (like maybe 36%?)

 

[Astro826]

Sure. I'll show you the screenshots I have right now, but tell me if you want me to detail a step in particular.

After the Moon transfer, I was left with 70% of fuel, and 2942.7 m/s of ΔV:
View attachment 122453

This is when I'm about to encounter Venus: 69.8% of fuel, 2936.3 m/s of ΔV:
View attachment 122454
I didn't realize myself I used that little fuel... I used the approach lines to plan my encounters largely in advance. It occured that I could anticipate an encounter 15 orbits before it happens, and the correction is very very cheap in this case. Especially that I usually use every fly-by opportunity to adjust my trajectory for the next encounter, like here:
View attachment 122458

Upon the first encounter with Mercury, my fuel has barely dropped:
View attachment 122455
This is because I usually perform 2 Venus assists. The first one sends me on a resonant orbit of ratio 4:3 (my ship orbits four times when Venus orbits three times), then the second one sends me towards Mercury perihelion.

For the V-leveraging steps I don't have all of them, but I have this one:
View attachment 122456
60.3% of fuel and 2684.4 m/s remaining at that stage.

Finally, Mercury orbit:
View attachment 122457
51.9% of fuel, 2444.7 m/s remaining.

I noticed that the remaining fuel there could depend a lot on your ability to aim for an insertion when Mercury is at the perihelion, which is explained by a bigger Oberth effect from the Sun. A first attempt left me with 29% of fuel after landing, because I was less efficient on this point.

Finally, a good landing technique, when you comes to a stop right above the ground so that the powered descent is minimal can make you gain a few tenths of percent point:
View attachment 122459

This is the corresponding screenshot:
View attachment 122460
The landing consumed 667.4 m/s of ΔV overall.

It indeed looks like the difference was all in the V-leveraging. I also had 70% fuel left after all the gravity assists before that. I may revisit this portion of the mission and see what I can do . Glad that I could match the computer in terms of all those gravity assists, but ANAIS still knows how to find the most optimal burns that are needed for V-leveraging.