Help me get my boys home.

[PakledHostage]

Well, I did some (gasp!) math...

Starting with these assumptions:

1. That the problem can be approximated as a 2D problem.

2. That you are in Eve orbit at UT = 185 days

3. That your starting Eve Pe is 102 km

4. That your starting Eve Ap is 5065 km

5. That you have 1500 m/s delta-V available

6. That the orbital characteristics of Kerbin and Eve given on the Wiki are valid for the version of the game you're playing

7. That you have enough fuel left over after performing these burns to trim your orbit, including any plane change manoeuvres that may be required.

Given assumption 3 and 4, your speed at Eve Pe should be 4230 m/s.

Given assumption 2 and 6, Kerbin should be about 183 degrees ahead of Eve at your current UT

If you wait 47 days in Eve orbit, Kerbin will then be 47.4 degrees ahead of Eve. Starting at that time (UT = 232 days), boost into an orbit about Kerbol having Pe = Eve's orbital radius, Ap = 18.8 million km. An object in this orbit will cross Kerbin's orbit in 20 days. If you do your burn right (i.e. such that the transfer orbit's longitude of periapsis is the same as Eve's true anomaly at the time of the burn), then your spacecraft will encounter Kerbin as it crosses Kerbin's orbit. You’re going to be going pretty quick when you encounter Kerbin and you’re crossing its orbit at a large angle, so you’re going to have to be very precise.

An object in orbit about Kerbol with Pe = 9.5 million km and Ap = 18.8 million km has a speed of 12.62 km/sec at periapsis.

Eve has a speed of 11.025 km/sec at the time you start your transfer.

You therefore need a speed of 1.597 km/sec at Eve's SOI in the prograde direction.

You'd have to be pretty lucky for the geometry to work out just right, but you might be able to fiddle the manoeuvre nodes to achieve the correct transfer orbit using the fuel you've got available if you start your burn some time on UT = 232 days.

If you are lucky enough to be able to do your transfer burn at Eve Pe (i.e. 102 km), you will only need to boost from 4230 m/s to 4756 m/s to reach the required escape velocity. That's only just over 500 m/s and well within your delta-V budget. Even if you're only able to get close to burning at Eve Pe, it should be possible to trim your orbit for a Kerbin encounter/aerobraking using only the fuel you have remaining after your transfer burn if you are careful.

No guarantees that any of the above will work for you because I don't know if I got the assumptions right, and I might have made a mistake somewhere in my haste to finish this on my (now extended) lunch break... It is worth a shot though. If it works, it will get your boys home in about 67 days.

I am, however, pretty sure it will work out fine if the assumptions are correct. I used the same method to plan my Proof of concept Duna Cycler trajectory.

Godspeed, Kermen!

Edited July 18, 2013 by PakledHostage

[Awkarran]

I really want to see how this ends. Best of luck!

[Scotius]

Good luck MG! I hope everything will work, and you get your crew home alive and well. ()b

[llamatoes]

Want to have something worse?

1400 delta v, life support and a retrograde Duna orbit. That was awful.

[AmpsterMan]

Hey Moon Goddess, upload your persistance to Mediafire and make a challenge on the challenge section of the forum. I think this way we can all take a stab at it.

Pretend it's mission control going through the simulations

[Nao]

@PakledHostage I may have messed up something but on a fresh save UT 1year and 185days gives us Eve ~40deg before Kerbin, so after 47 days of waiting in Eve orbit, Kerbin is not even close to 47deg ahead of Eve.

From Alex site it looks like if he escapes Eve immediately at an angle (173deg to Eve prograde, while standard hoffman have 163) he'll arrive at Kerbin in 83days. From 100km parking orbit it takes 1642 Dv so depending on how exactly the elliptical orbit is situated he might save the Kermans

GL! Keep us updated. Or even better upload the persistence file as AmpsterMan suggested!

[PakledHostage]

@PakledHostage I may have messed up something but on a fresh save UT 1year and 185days gives us Eve ~40deg before Kerbin, so after 47 days of waiting in Eve orbit, Kerbin is not even close to 47deg ahead of Eve.

No, sounds like I screwed something up in my analysis... I cobbled a spreadsheet together earlier today to do it, but I didn't check my results against the map view. Now that I have the spreadsheet, it will be easier to re-do it though. It looks like it should be possible to bring them home.

I like AmsterMan's suggestion of posting the persistence file as a challenge. I will give it a try myself if MoonGoddess posts the persistence file.

Edit 1: I found my bug... I had defined Kerbin's orbital period as 106 days + 12 hours + 32 days + 24.6 seconds. Stand by one...

Edit 2: Upon further review, I think Vostok's suggestion of using an orbit that has its Pe inside Eve's orbit may be required. I don't see a window for the type of transfer I described earlier opening in time to save our heros. Alternatively, Johnno's suggestion of sending a rescue mission from Kerbin that will arrive within the requisite 85 days may be required.

Edited July 18, 2013 by PakledHostage

[Moon Goddess]

Here's the challenge http://forum.kerbalspaceprogram.com/showthread.php/40891-Get-my-boys-home-from-Eve-before-the-air-runs-out?p=526120#post526120

[AustralianFries]

Well, yes technically. I'd probably send a refueling probe to save them, but since you're in an elliptical orbit that may be challenging for you. What you may want to do is get into a solar orbit and then dock, but solar orbit dockings aren't so great. Hmm... I say just quicksave before trying, and if you don't get it, try again.

Edit: 400th post, for the second time (Forum Account Slaughter)

[astropapi1]

Hope you get them home. It's nice to see someone cares about their lives.

Good luck!