Visiting moons

[Rylant]

Hey all, 

So when visiting the various moons of the solar system, is there anything special to get an encounter with them? I am looking at heading to Ike. So is it just a normal visit to Duna, and from Duna’s orbit, burn to encounter Ike, hang out there until I am done. Then return to Duna orbit and go back to Kerbin? I assume you don’t look for an Ike encounter right from the orbit of Kerbin?

I also know that Jool has many moons. I am not ready yet to reach them but was wondering if it is the same for them. Jool orbit, and then off to Vall or Tylo?

 Thanks

 Rylant

[bewing]

Ike is so big that it's actually really hard to miss it. Any craft orbiting around Duna that has an Ap within a million meters of Ike will rapidly find itself in an encounter with Ike. When the Ike/Duna system was created in the game, that's specifically what makes that pair of CBs challenging -- plus the fact that Ike is in a synchronous orbit.

Visiting other moons is just like visiting the moons of Kerbin. It's easiest to visit the moons first, then bleed off energy to visit the planet last.

That is, before you reach your target's SOI, adjust your flyby to give you a really low Pe. Burn just enough at your Pe to lower your Ap into the SOI. Then adjust some more to encounter the outermost moon, and work your way inward after each encounter.

Edited April 26, 2021 by bewing

[king of nowhere]

the moons of jool are an entirely different story, as they are basically their own miniature subsystem.

first, no need to make injection burns at jool ever, you can use laythe or tylo to get a gravity assist and get captured in the system. second, once you are on a moon, visit them in sequence. a transfer between laythe and vall uses the same principles, on a much smaller scale, as a transfer between kerbin and duna.

when i visit them, i prefer to go for tylo first, because it requires a very big lander, and using it first i don't have to cart it around for the rest of the mission. laythe second, for the same reason.

[Philae_Rosetta2021]

Oh...

I just aim for the planet and then when I am there make little changes for encounters. That is what I did for Vall. Jool traj. then circularise orbit, then Vall encounter. As Vall is quite small (I think) it was really hard for me to get an encounter straight away. It also needed 2000 dv for me to circularise, but that just might be because I had 9 fuel tanks and nuclear engines, plus a lander.

Do you recommend this approach for smaller moons? I know it takes more dv, but it is a more sure way of doing it, in my experience.

[king of nowhere]

6 hours ago, Philae_Rosetta2021 said:

Oh...

I just aim for the planet and then when I am there make little changes for encounters. That is what I did for Vall. Jool traj. then circularise orbit, then Vall encounter. As Vall is quite small (I think) it was really hard for me to get an encounter straight away. It also needed 2000 dv for me to circularise, but that just might be because I had 9 fuel tanks and nuclear engines, plus a lander.

wrong. deltaV spent is irrelevant of the ship's mass. the ship's mass affects how much deltaV you can get from the same amount of fuel, but that established, 2000 m/s is 2000 m/s, no matter what.

Quote

Do you recommend this approach for smaller moons? I know it takes more dv, but it is a more sure way of doing it, in my experience.

the problem with your approach is that you miss oberth effect. the injection burn is more efficient if you perform it closer to the biggest source of gravity around; so it is cheaper to make it around the planet than around the moon - which is itself cheaper than making it far away from the planet. once you are in a jool intercept, you can end in a circular vall orbit with 1000 m/s easily without gravity assist, and you can do it with as little as 500 m/s with advanced gravity assists.

[Philae_Rosetta2021]

Thank you very much @king of nowhere. I will bear that in mind next time I have a short holiday near Jool. ;)