Advanced Question Transfering to Europa with low encounter speed

[Shadow Addict]

I'm attempting to get to Europa using TransX. I made the flight but ended up with a very high encounter velocity (14 km/s) that made it impossible to insert into orbit. Further attempts at planning it result in a similarly high encounter vel. How can I get to Europa at a slow enough velocity for orbit insertion?

 

[insanity]

Did you insert yourself into Jupiter's orbit first? I've had problems nailing Eruopa without slowing myself down a bit. I'm thinking that the trajectory you had still had you ejecting out of Jupiter's SOI, which would take a sizeable amount of energy to brake and then inject into Europa orbit.

 

[Shadow Addict]

No, I didn't. I was hoping for a more direct route without JOI, but it makes sense that it's necessary.

 

[insanity]

What I usually do is get into Jupiter's SOI using transx (which is just more fun to plan with) and then set up an approach plan in IMFD that has me inject at a low relative inclination to Europa about 100M below its orbit (averaging PeA and ApA for Europa). Then it becomes more or less like a sync orbit. Either transx or IMFD will get you there pretty quickly and a low-enough relative velocity in respect to Europa to brake.

I'm sure flytandem could tell you a better way to do it, probably without wasting a drop of fuel either, but I can vouch for my method at least getting you there.

 

[Shadow Addict]

I agree that TransX is more fun to plan with, though I LOVE IMFD's autoburn and I still use it for tedious, standard things like orbit insertion. I'll try your method now.

EDIT: Lame, I can't get my RInc lower than about 26 degrees on the Planet Approach screen. I guess I have to redo the TJI.

 

[McWgogs]

Note also that Europa's speed varies a lot relative to the Sun over it's orbit around Jupiter (almost stops when it's right in front of the lit side) so you might want to adjust your arrival time and see what happens.

 

[flytandem]

I know that it's possible to get a stock deltaglider from surface start on Earth to a landing on Europa but is does use most of the fuel. It's not easy.

The trick is to plan an arrival at Europa tangentially. Meaning that by the time you are half way to Jupiter you should be planning on arriving with the same orbital height as Europa, at a node with Europa (place the white line on the Jupiter Pe point) and also timed to arrive at the same time that Europa is there. This way the orbital velocity of Europa around Jupiter is subtracted from your orbital velocity, making the relative velocity at Europa far less.

When you are most of the way to Jupiter, if you are pointed prograde in your orbit relative to the sun, you will probably see Jupiter at about your three o'clock position (on your right). Doing a mid course correction with a maneuver you will probably notice that ...
changes in prograde mostly cause changes in orbital height at Jupiter,
changes in plane change mostly cause the node to shift (white line),
changes in OUTWARD mostly cause the timing of the arrival to change which helps get Europa to be there WHEN you get there.

Finally a little hint that most don't know about is, try to do your last MCC just before the TransX stage switches to Jupiter centered. Then after the switch don't worry if initially the cl app to Europa looks off. It will normally look bad at the start of this stage but as you get closer it will become very much like what you had just before the switch of stages. Watch the cl app value change and after a while as you get close the rate of change drops to near zero. At that point do a final correction so you arrive at Europa with a low ground clearance like 50 or 100 Km agl.

I have always wondered about the need for a way to know when the stages in TransX are about to switch, like a bar filling in. Like a thermometer. When it reaches the end the stage switches. This way you can warp ahead to just before the switch and do you final MCC then. My workaround until then is to watch the gravity value in Orbit MFD. When jupiter is around 0.15, I go for the last MCC. Or you could do a save at about .10 and then run the sim to watch when the stage switches then quit restart to plan your final MCC just before the switch.


rob

 

[Shadow Addict]

I'll try that. Thanks again for the help!

EDIT: As always, you explained it in an intuitive and easy way. I just put myself into a 159x740km orbit after a 5km/s Europa orbit insertion burn. Thanks again again!