Altaïr's crazy stuff

[Axiom]

ANAIS still knows how to find the most optimal burns that are needed for V-leveraging.

The problem is that ANAIS can look many orbits ahead to find paths while the stock navigation system can only look one orbit ahead and crashes your game occasionally

 

[Dahzito]

Sure. It consists in using the Moon to perform gravity assists.

I was going to see the explanation Astro826 posted here but thank you for the explanation!

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:

I see, idk why but that remembers me of the Artemis 1 flight path, except that the second fly-by ejects the spacecraft of Earth.

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:

Interesting, I usually had the though that it was just not worth to make gravity assists with the moon on these types of situations, also because of the fuel wasted on the transfer burn to the Moon that is similar to the amount of fuel wasted on a transfer burn to Venus.

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...

Already heard of the Third Kepler law but never used it on practice, also because there is now ANAIS.
Tricky question on what Astro826 went through

From what I saw here another important thing on this mission was also the V-leveraging with Mercury, already tried that with Mercury but always had the problem of changing the orbit not the way I wanted (decreasing the periapsis), but I guess that this is obviously not the easiest part.

 

[Altaïr]

From what I saw here another important thing on this mission was also the V-leveraging with Mercury, already tried that with Mercury but always had the problem of changing the orbit not the way I wanted (decreasing the periapsis), but I guess that this is obviously not the easiest part.

You're supposed to burn prograde at the apoapsis to raise the periapsis. Then each new fly-by will decrease your apoapsis but also your periapsis. That's why you have to raise it again after each fly-by. As long as you make fly-bys, make sure your trajectory slightly crosses Mercury's orbit. But once you plan your capture, make it tangent as closely as possible. This is to minimize the encounter speed.

 

[Astro826]

Artemis 1 flight path

That orbit was more of a three body problem, it was between a super elliptical lunar orbit and two close passes of the moon, it went quite far out.

Interesting, I usually had the though that it was just not worth to make gravity assists with the moon on these types of situations, also because of the fuel wasted on the transfer burn to the Moon that is similar to the amount of fuel wasted on a transfer burn to Venus

The ∆V difference of a lunar Homman transfer and a flyby of Venus with enough velocity for gravity assists to Mercury is ~150 m/s.

 

[Marmilo]

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

To think that I was proud of doing it with like 2% left...
At least I was the first person who did the challenge (publicly) I guess

 

[Axiom]

To think that I was proud of doing it with like 2% left...
At least I was the first person who did the challenge (publicly) I guess

The first person to do something will always have it the hardest.
Also you did it with circular orbits and I'm not sure if that makes it easier or harder

 

[Altaïr]

Oh, it's true that orbits were circular at the beginning of 1.5. The challenge was probably a little easier then.

 

[Astro826]

Oh, it's true that orbits were circular at the beginning of 1.5. The challenge was probably a little easier then.

Definitely easier in practice a you don't have to worry about periapsis/apoapsis. It may be possible that it took more delta V though, I'm not aware of how exactly Mercury's orbital height changed. The fact that Mercury is on an elliptical trajectory where you can encounter at periapsis makes the flyby slower.

 

[Altaïr]

Definitely easier in practice a you don't have to worry about periapsis/apoapsis. It may be possible that it took more delta V though, I'm not aware of how exactly Mercury's orbital height changed. The fact that Mercury is on an elliptical trajectory where you can encounter at periapsis makes the flyby slower.

Most likely true technically speaking. But the fact that Mercury has a lower periapsis also forces the player to chain two gravity assists (I believe a single one was enough before) or to spend fuel to power a single gravity assist. And if you only rely on gravity assists you need to leave Earth with more energy than before for this to work.

Technically speaking it's definitely harder now. But in terms of ΔV (supposing it's done properly) I'm not even sure it's better since you partly lose on one side what you gained on the other side.

 

[Astro826]

Technically speaking it's definitely harder now. But in terms of ΔV (supposing it's done properly) I'm not even sure it's better since you partly lose on one side what you gained on the other side.

That's where the difference in orbital height matters. Do you know how it changed when orbital eccentricity was added?

 

[Altaïr]

That's where the difference in orbital height matters. Do you know how it changed when orbital eccentricity was added?

I believe that the sma was kept the same and that eccentricity was added, but I'll have to check that. I should still have the spreadsheet that helped me to calculate the transfers for the ΔV map, the old values should be in it.

 

[Altaïr]

That's where the difference in orbital height matters. Do you know how it changed when orbital eccentricity was added?

OK, I checked, I confirm that the sma was kept the same, only an eccentricity of 0.2 was added for Mercury.

Using both the game and my old calculation file, I tried to make an interactive comparison to make things as simple as possible.
First, I simulated a transfer from Venus to Mercury's periapsis (since aiming for Mercury at periapsis is the best solution).
This is how it costs now:

ΔV(departure) = 1197.3 m/s
ΔV(arrival) = 714.6 m/s

This is what it costed before:

ΔV(departure) = 951.1 m/s
ΔV(arrival) = 1061.9 m/s (calculated by hand using the value on screenshot since the planet influence is not accounted for)

What's interesting here is the arrival ΔV, since after a gravity assist it will be like if you were going to Mercury coming from Venus.
The arrival to Mercury was 347.3 m/s more expensive before. In practice both value could be reduced through V-leveraging, but this is still very significant.

Now let's try to see what it would have costed to launch from Earth to reach the required velocity as Venus level...
Due to the velocites needed at exit, the difference of velocity with Venus (in the Sun's frame of reference) should be:
ΔV (now) = 1668.2 m/s
ΔV (before) = 1225.5 m/s

I've had to make the calculations by myself (Thanks that Venus and Earth orbits are still circular!), here are the transfers that should be performed in theory.
Now:

Before:

Those represent... 40.3 m/s of difference, in favor of the previous situation. Not terrible.

So, as a summary:
- The burn from Earth costs 40.3 m/s more now compared to before orbits were made elliptic
- The insertion burn on Mercury costs 347.3 m/s less than before, eventually reduced by V-leveraging. From my saves, I could estimate a ΔV reduction of 37% using this technique, so the difference would be 218.8 m/s in this case.

Overall, compared to before, the trip is cheaper by 307.0 m/s without V-leveraging, by 178.5 m/s with it. In terms of fuel, this represents a difference of 4.1% or 2.3%.
In a challenge in which the difference between a failure or a success is sometimes smaller than 1%, this is a noticeable difference.

You were right Astro826 , I didn't think the difference would be that much to be honest. This supposes that the trip is managed in a close to optimal way though, since it's much easier to screw up with elliptical orbits!

 

[Astro826]

You were right @Astro826 , I didn't think the difference would be that much to be honest. This supposes that the trip is managed in a close to optimal way though, since it's much easier to screw up with elliptical orbits!

Yeah I suspected the higher velocity of Mercury at perihelion played a significant role, thanks for doing the math! It really does make a difference to make encounters where your fastest and slowest points align.

 

[Axiom]

You were right @Astro826 , I didn't think the difference would be that much to be honest. This supposes that the trip is managed in a close to optimal way though, since it's much easier to screw up with elliptical orbits!

So that is why I believe you were able to lanf without gravity assists, the challenge got less delta-v intensive

 

[Altaïr]

So that is why I believe you were able to lanf without gravity assists, the challenge got less delta-v intensive

That probably helped. I checked with the ΔV map, in theory you would need 2784 m/s to reach Low Mercury Orbit, plus let's say 680 m/s for landing, which is reasonable from my tests. That sums up to 3464 m/s. The same calculation in the new configuration gives 3191 m/s which saves 273 m/s.

However the ship has 3597 m/s of ΔV so in theory it should work. The reason why it doesn't in practice is the gradual loss of Oberth effect on prolongated burns, but this is also true in the new configuration.

What was determining was the use of ANAIS that appeared to be more effective than the Vanilla navigation system. Without ANAIS I already tried, I was not even close.

 

[Altaïr]

Playing again with my flagship

I must say I prefer it that way, cleaner, without too many details.

Time to try it again!


And guess what is my payload?

Yes, my trashy shuttle! The union of the best and the worst!
It was so desperate to reach orbit in realistic that I decided to give it a hand.

In the end...

 

[floatingfuel]

View attachment 123887

Majestic!

View attachment 123890
View attachment 123891 View attachment 123892

LOL, are you going to store the fish on Europa, or roast it on Venus?

 

[Altaïr]

Majestic!
LOL, are you going to store the fish on Europa, or roast it on Venus?

Ah, a good fish roasted by sulfuric acid fumes, I don't say no...

Since I have a full TtTOtW (It's the "Truly the Trashiest Of the World", remember?) in orbit, it should be able to reach Venus by itself, even in realistic:


Then reaching Venus orbit is easy:


The TtTOtW can deliver its payload before reentering:

It managed to deliver a payload in Low Venus Orbit in realistic! Even if it was helped a little.

Now, time to burn!

Actually it was quite well designed for reentry, the fish doesn't want to burn...

Anyway, once landed, it won't go anywhere.

 

[Altaïr]

It's been long I haven't done something significant in SFS... What about a Venus return mission in realistic? That sounds reasonably easy to start playing again after a few months of inactivity.

In serious, that will be an ambitious mission. I'll use a few mods for this one, which notably include:
- VanillaUpgrades
- ANAIS
- Delta-V calculator
- SmartSAS
- Aero trajectory
- Gliding heat shields
- InfoOverload

This will be the ship I'll use for this mission:

As is, it's way too heavy to be launched in a single launch, so I'll have to send it in 4 launches, and assemble it in LEO.

Here is the first part of the assembly:

This part is the transfer module. Yes, I'll have to burn all that fuel just to transfer to Venus. Now it's time to launch the lander itself. Which is a whole rocket in itself since it has to reach Venus orbit after landing.
I'll use my favourite launcher of course...

Which officially qualifies it as a launcher launcher in realistic

Then time to assemble the "umbrella", that will be charged to make the lander slow down enough during reentry:

Then finally, I dock it to the transfer module:

Now it's time for the transfer itself:

This is terribly long, but finally...


The two annex tanks are now empty, so they are thrown into the venusian atmosphere. Then the ship is reassembled for aerobraking, because I wouldn't have enough fuel to reach low Venus orbit...


It's now time to attempt the very risky aerobraking maneuver. Fortunately, Gliding heat shields and aero trajectory are especially useful for this...

Then the transfer module finishes the satellization in low orbit before being thrown into Venus aswell. Only a small refuelling unit is left in Venus orbit. It's the small part with the probe attached. It doesn't even have an engine, only a pair of RCS.
Then, time for the deadly reentry!

The design is efficient and does its job. the gliding heat shields helped to aim for a relatively flat landing zone. Then the landing itself combines the use of parachutes and the main engine after the heat shield has been jettisoned:

Finally, we are there!

But we've made only half of the trip, we have to return! Who would like to stay in such a hellish place anyway...
So, lift-off...

The ship finally reaches Venus orbit where there's a little refueller to refill it.


The transfer for the return is quite simple at that stage.


And finally, I'm back!

A difficult one to get, especially in realistic. The "extreme" rating is largely deserved

 

[Altaïr]

While I'm at it, I thought I could try to complete all the challenges proposed by the game, since I already have a nice collection of them...

So here are the asteroid missions!
I'll use a small ship for that, no need to go big.


The transfer is a formality...


We have an impact mission to fullfill, so I decided to call an old friend that will pilot the capsule until it crashes. He was the perfect guy for that job.

Then the landing of course.


This makes a nice collection, even if the remaining ones won't be easy

 

[Lemniscate Biscuit]

While I'm at it, I thought I could try to complete all the challenges proposed by the game, since I already have a nice collection of them...

So here are the asteroid missions!
I'll use a small ship for that, no need to go big.
View attachment 132947

The transfer is a formality...
View attachment 132948

We have an impact mission to fullfill, so I decided to call an old friend that will pilot the capsule until it crashes. He was the perfect guy for that job.
View attachment 132952

Then the landing of course.
View attachment 132949 View attachment 132950

This makes a nice collection, even if the remaining ones won't be easy
View attachment 132951

Nice work ridding the world of another foe.

 

[Darthan]

It's been long I haven't done something significant in SFS... What about a Venus return mission in realistic? That sounds reasonably easy to start playing again after a few months of inactivity.

I realised that I have never attempted a Venus return in Realistic without using custom parts so I tried it. Wasn't able to go below 4 launches so it was rather similar to your run. Rather than using a specialised transporter I simply left the lander attached to the third stage of its launcher and refueled the third stage.

The third stage had two engine types, a Titan and a 2 Valiants. I switched off the Titan once it had reached orbit. I also experimented with the launcher rather than using one I had already designed.

The lander plus launcher:


The legs and parachutes to be attached in orbit, plus some fuel:


The tanker use for the remaining fuel (needed two of these):


Venus Aerobreaking:


Venus landing:


Earth return (fuel was a bit tight)


Mission Log:


I took 90 screenshots in total. Let me know if you are curious about any details.

 

[Altaïr]

I realised that I have never attempted a Venus return in Realistic without using custom parts so I tried it. Wasn't able to go below 4 launches so it was rather similar to your run. Rather than using a specialised transporter I simply left the lander attached to the third stage of its launcher and refueled the third stage.

The third stage had two engine types, a Titan and a 2 Valiants. I switched off the Titan once it had reached orbit. I also experimented with the launcher rather than using one I had already designed.

The lander plus launcher:
View attachment 132968 View attachment 132969

The legs and parachutes to be attached in orbit, plus some fuel:
View attachment 132970 View attachment 132971

The tanker use for the remaining fuel (needed two of these):
View attachment 132972

Venus Aerobreaking:
View attachment 132973

Venus landing:
View attachment 132974

Earth return (fuel was a bit tight)
View attachment 132975

Mission Log:
View attachment 132976

I took 90 screenshots in total. Let me know if you are curious about any details.

Nice, interesting design too. I see you managed to do it with a lighter launcher aswell. I needed the same amount of launches, but I took advantage of my optimized Sapphire launcher, that can carry up to 150 tons in LEO.

My launcher (the one I land and launch from Venus) could have been simpler and lighter however. For example, there's a pair of landing legs on the second stage that was never used. That's because I wanted to try a ship that had the capacity to land on other bodies after Venus. But the landing legs made the ship wider, so more draggy, so I had to add fairings. But even like that I had to add 2 Kolibri engines to the first stage to give it more punch.
I didn't consider landing on Maxwell Montes either (which is absurdly high in the game by the way...), where drag is a much lighter problem.

In short, I did it the hard way

Your lander/launcher seems particularly efficient though. Did you need to dock in Venus orbit to refill your stage before returning to Earth?

 

[Marmilo]

Nice, interesting design too. I see you managed to do it with a lighter launcher aswell. I needed the same amount of launches, but I took advantage of my optimized Sapphire launcher, that can carry up to 150 tons in LEO.

My launcher (the one I land and launch from Venus) could have been simpler and lighter however. For example, there's a pair of landing legs on the second stage that was never used. That's because I wanted to try a ship that had the capacity to land on other bodies after Venus. But the landing legs made the ship wider, so more draggy, so I had to add fairings. But even like that I had to add 2 Kolibri engines to the first stage to give it more punch.
I didn't consider landing on Maxwell Montes either (which is absurdly high in the game by the way...), where drag is a much lighter problem.

In short, I did it the hard way

Your lander/launcher seems particularly efficient though. Did you need to dock in Venus orbit to refill your stage before returning to Earth?

Yeah, Maxwell Montes is what made my 6 part Venus return possible

 

[Darthan]

Your lander/launcher seems particularly efficient though.

Being fairly light I was able to use asparagus staging:

I noticed that I had missed setting up the fuel transfer when I paused the game to take the screenshot for the launch and staging events. Which is why the upper stage was not quite at 100%.

Did you need to dock in Venus orbit to refill your stage before returning to Earth?

Yes, however I did not have enough fuel left to fill it up and depended on the safety margin to get back: