Question The Jupiter Moons

[SpecialKaye87]

I've got an orbit going around Jupiter, I discovered early on that I had to maintain that big orbit in order to avoid falling into Jupiter.
My goal was to land on Europa, Callisto, Ganymede (any moon would be great), but I've had trouble doing so.

I've tried IMFD course
I've tried manually doing it with TransferMFD

The problem comes when I try to maintain orbit around Europa. I either smash into the planet or I skid right past it while trying to retro burn.

I've tried both aligning planes and doing off-plane transfers but I get mixed results. Any insight here?

 

[Tychonaut]

The Europa to Callisto video tutorial on this page may help you. It certainly helped me figure out how to transfer to and from Jupiter's moons. Once you're in a circular orbit inside a moon's SOI, landing should use the same basic skills (or MFDs) as landing on Luna.

 

[SpecialKaye87]

yea, I thought it would be easy too but for some reason I get going so damn fast that retro burn just has way to much dV for me to burn off. Maybe I'm orbiting Jupiter so close that my escape velocity leaves me with extra momentum.

 

[Tommy]

You don't need escape velocity - Jupiter's moons are all inside Jupiter's SOI. If you are starting from a fairly low Jupiter orbit, you may want to raise your orbit before attempting the transfer - this will reduce the relative velocity to the moon and leave you with a shorter insertion burn.

 

[statickid]

sounds like something intrinsically wrong with your method, what kind of transfers are you making that cause you to fly past moons so fast?? If you are starting at a lower orbit and transfering out of it you should be going "slower" than the moon when you intercept it. maybe you need to speed up instead of retro burning

 

[Tommy]

I suspect that's the case, but remember that when he gets to the moon he's using the local frame, so it's always a retro burn relative to the local body - even if it's prograde relative to Jupiter.

The difficulty is that Jupiter's gravity is so strong that the moons have very small SOI's. By the time you get into the moon's SOI, it's too late to begin the burn - it should have started before you even get inside the moon's SOI.

That's why I recommended raising the orbit first, so the insertion burn is short enough that you can wait until you are inside the moon's SOI.

 

[statickid]

In Jovian and uh...saturn..ian orbits the information is not always very accurate when using only one reference. I usually switch back and forth between reference of the moon and jupiter treating the insertion more like a station rendezvous.

 

[statickid]

I dont think its so much that the soi's are tiny its just the predictions made by the MFD are too simple to take all factors into account. when you first synchronise the orbit with the moon you can find that a very eccentric orbit will be possible

 

[SpecialKaye87]

you guys want me to just post the scn file so you can get an idea of what I've got to start with? btw, how the hell do you post an scn file? copy and past the actual text?

 

[Tommy]

I dont think its so much that the soi's are tiny its just the predictions made by the MFD are too simple to take all factors into account. when you first synchronise the orbit with the moon you can find that a very eccentric orbit will be possible

That's true, the stock MFD's aren't very accurate in this case. I use IMFD's Map, which does a much better job because it presents a multi-body prediction, while the stock MFD's only consider the reference body and vessel.

Still, I think the small SOI presents a problem. If you start from a low-ish Jupiter Orbit, when you get to, say, Europa you will find that you pass through the SOI in about 20 seconds - yet your insertion burn is 40 seconds or more. So you have to start the insertion burn before you enter Europa's SOI. Since the Autopilot autmatically references the major gravity source (which will be Jupiter) you have to set an OrbitMFD to reference Europa, hit the HUD button, and manually align with the retrograde vector. You'll still have some inaccuracy since that vector doesn't consider Jupiter's SOI, etc, so I would say that both factors (SOI and MFD accuracy) together are what make it so difficult.

you guys want me to just post the scn file so you can get an idea of what I've got to start with? btw, how the hell do you post an scn file? copy and past the actual text?

There are two ways to post a scn file. One is to copy/paste all the text (and ensure it is wrapped in "Code" tags to preserve the formatting). The other is to attach the file (hit the paperclip icon when posting to upload the file), which is easiest for all of us.