Can I go back from Eve ?

[0__0]

Hi, I'm currently in a Eve orbit with: PE: 164.510m / AP: 3 096 134m and 927m/s of DeltaV. Is it possible for me to go back to Kerbin with this setup or do I need a rescue mission ?

[Vanamonde]

Add up the numbers between where you are and where you want to be. 

 

Looks like you're coming up short. Time for a rescue mission.

Also, thread moved to the Gameplay Questions subforum. 

[Dirkidirk]

you're 800 delta-V short, Time to call THE BLUNDERBIRDS!

that's a reference to something on the youtube, if you didn't already know.

 

[Snark]

5 hours ago, 0__0 said:

Hi, I'm currently in a Eve orbit with: PE: 164.510m / AP: 3 096 134m and 927m/s of DeltaV. Is it possible for me to go back to Kerbin with this setup or do I need a rescue mission ?

Here's the tool that I like to use:

http://ksp.olex.biz

Just put in your origin (Eve), the height of your parking orbit (let's call it 150 km), and your destination (Kerbin), and it does all the math for you.  In this case it's saying  you'd need an ejection burn of 1338 m/s.

So no, you don't have enough dV; you're just over 400 m/s short.    (And that's assuming a perfect transfer window; you'd need more if the planets aren't correctly lined up.)

[Starman4308]

Clearly the answer is a series of Gilly gravity assists.

A more serious answer: send a rescue mission. While I'd have to double-check with actual math, I suspect you're not going to get enough dV to pull off something like EEK, where you eject from Eve, encounter it N orbits later (it helps to make an N:N+1 resonance), and use that slingshot to send you to Kerbin.

[James M]

20 minutes ago, Starman4308 said:

Clearly the answer is a series of Gilly gravity assists.

Yep. I think gravity assists over a seriously long amount of time might be the only way to pull that off. (Would it be possible to dive down to moho coming from behind it and kick yourself up to kerbin's altitude?)

Edited March 12, 2020 by James M
Afterthought?

[Dirkidirk]

33 minutes ago, James M said:

Yep. I think gravity assists over a seriously long amount of time might be the only way to pull that off.

yes, if the moon actually had any mass. gilly is VERY small, and it's sphere of influence is tiny. although if @0__0 feels like it, they can use the remaining Delta-V to land on gilly and plant a flag while they wait for their rescue vessel. Because why Not!

41 minutes ago, James M said:

Would it be possible to dive down to moho coming from behind it and kick yourself up to kerbin's altitude?

sadly, no, as it (according to this website) would take even more Delta-V to get to moho.

 

7 hours ago, 0__0 said:

Hi, I'm currently in a Eve orbit with: PE: 164.510m / AP: 3 096 134m and 927m/s of DeltaV

New answer! I misread your post, and discovered that you have an apoapsis of 3000000. if you didn't already send a rescue mission, check if you can go back to kerbin with your 927m/s, by placing a maneuver node at periapsis.

[Starman4308]

54 minutes ago, James M said:

Yep. I think gravity assists over a seriously long amount of time might be the only way to pull that off. (Would it be possible to dive down to moho coming from behind it and kick yourself up to kerbin's altitude?)

There are two problems, both of which are fundamentally because Gilly is way too small for practical slingshot maneuvers.

1) Unless you can borrow NASA's supercomputers, you're going to waste more dV setting up Gilly encouters than anything GIlly actually gains you.

2) Even if you could set up the slingshots with superb precision, it would take a very long time, as each slingshot provides only a very small boost.

It'd also be impossible to use Gilly for the final gravity assists. You'd need to use Gilly to kick yourself into a Kerbol-centric orbit, and then use at least a few Eve encounters to boost up to a Kerbin-crossing orbit. Eve is a practical slingshot target, but slingshots work poorly when relative velocities are low (as would be the case from a "just barely ejected from Eve" orbit), so you'd need several slingshots just to build up some Eve-relative velocity.

Now, if he had a bit more dV to spare, I might suggest kicking himself into a Kerbol-centric orbit and using Eve slingshots to go to Kerbin, but with the dV he has and the absence of any practical gravity assist target within Eve SOI, he's basically stuck without a rescue mission.

[Superfluous J]

43 minutes ago, Dirkidirk said:

New answer! I misread your post, and discovered that you have an apoapsis of 3000000. if you didn't already send a rescue mission, check if you can go back to kerbin with your 927m/s, by placing a maneuver node at periapsis.

Note also after placing the maneuver node, to try clicking "next orbit" a few (or a lot of) times to make sure you're ejecting at the correct time. You can get vastly different solar orbits based on which direction you leave Eve and with your limited fuel budget and orbital path, your only effective way to change the direction you leave Eve is to do it at different times (i.e., orbits)

Still not sure if you have enough dV to reach home but as @Dirkidirk says, it's a much better possibility than if you were low Eve orbit.

Edited March 12, 2020 by 5thHorseman

[AHHans]

14 hours ago, 0__0 said:

Hi, I'm currently in a Eve orbit with: PE: 164.510m / AP: 3 096 134m and 927m/s of DeltaV. Is it possible for me to go back to Kerbin with this setup or do I need a rescue mission ?

As @Dirkidirk and @5thHorseman already mentioned: that eccentric orbit around Eve mean that you need less dV to leave Eve's SOI. And a quick check (with a test craft and the cheat menu) shows that only need ca. 500 m/s to get onto an orbit around the sun that reaches up to Kerbin's orbit if you burn at Pe at the right time. So, yes, it is possible to get back to Kerbin, if you wait for a good transfer window.

The best transfer window would be when a burn at PE will eject you from Eve's SOI in the direction that Eve is going around the sun and at the same time when there is a transfer window for a transfer from Eve to Kerbin. You can either wait for such a "double transfer window" to happen, or you can (try to) use the ca. 400 m/s spare dV to tune your transfer to get back earlier.

I would wait for a window when the ejection from Eve is in the right direction (which happens once every Eve-year) and then try to tune the transfer - including plane change burn in solar orbit - to get back to Kerbin. If that doesn't work out during the first window then I'd wait another Eve-year and try again, until it works. One thing to keep in mind is to plan out the whole trip with all burns in advance and to keep some dV as reserve for corrections. (In my quick&dirty test I needed 630 m/s for the Eve-ejection burn into an orbit well outside Kerbin's orbit and 250 m/s for a plane-change burn fairly close to the apoapsis.)

6 hours ago, 5thHorseman said:

Note also after placing the maneuver node, to try clicking "next orbit" a few (or a lot of) times to make sure you're ejecting at the correct time.

Well, in general that is an excellent suggestion but in this case the period of his orbit is less than three hours. And waiting for one Eve-year that way can get a bit tedious.

[Superfluous J]

1 hour ago, AHHans said:

 

7 hours ago, 5thHorseman said:

Note also after placing the maneuver node, to try clicking "next orbit" a few (or a lot of) times to make sure you're ejecting at the correct time.

Well, in general that is an excellent suggestion but in this case the period of his orbit is less than three hours. And waiting for one Eve-year that way can get a bit tedious.

Hehe I do it all the time, though usually it's "only" in LKO going to Minmus, 45 minute jumps for 15 (kerbal) days can get bland.

[James M]

21 hours ago, Dirkidirk said:

sadly, no, as it (according to this website) would take even more Delta-V to get to moho.

Rip well thanks for checking for me anyway 

[RoninFrog]

Sorta kinda.  If you are manned and by "back to Kerbin" you mean Kerbin orbit, then yes.  Burn all the fuel in your ship, get out, and use the EVA jetpack to get an eccentric Kerbin orbit.  There is only 600 m/s in the pack, so according to my map you will only have only 27 m/s to spare from a 100 km circular orbit around Eve.  Yours seems to be more eccentric (160 km x 3000 km) so if you can burn for Kerbin at Pe you should be okay.

Oh, and don't forget to grab the science.

Edited March 16, 2020 by RoninFrog