Ike Slingshot?

[Umlüx]

i am currently sitting in low Duna Orbit with about 1k dV left. i fear that is not enough for my return to Kerbin.

Ike is relatively big.. so i thought i try and slingshot me out of Duna SOI and then finish the burn for Kerbin. would this actually cost me less fuel than burning from LDO?

maybe i can even combine a LDO burn with a slingshot maneuver.. but this would be a rather hefty stunt i think..

Edited November 4, 2013 by Umlüx

[AndreyATGB]

It will but you'll have to eyeball the correct angle. Keep in mind you'll probably exit Ike at about 100 or so degrees from your original path, so you need Ike to be almost retrograde to duna's orbit, but not enough for your ejection angle to be screwed up. 1000dV is enough though, ejection burn is only ~600.

[Kasuha]

No eyeballing needed if you increase your CONIC_PATCH_LIMIT to about 6 in settings.cfg. Just place a maneuver and watch if you can hit Kerbin SOI.

[JiWint]

Don't use cheats ksp.olex.biz is a tool just for you. I just got from eve to kerbin in 1 burn and aerobraked

[boomerdog2000]

I had the same situation. You can probably make it with the conic limit turned up so you can see what you are doing. I did have to use the RCS on my lander to actually hit Kerbinl but Jeb, Bob and Bill were all returned safely. Long as you quicksave before burning you should be alright. Also don't timewarp too fast over SOI changes as this can mess up your projected path.

[blizzy78]

Don't use cheats ksp.olex.biz is a tool just for you. I just got from eve to kerbin in 1 burn and aerobraked

It's not a cheat to get more information displayed.

[Nao]

Don't use cheats ksp.olex.biz is a tool just for you. I just got from eve to kerbin in 1 burn and aerobraked

Lol, no offence, but you tell him to not use "cheats" while providing one yourself. I would consider using external tools that give knowledge you can't normally find in the game more "cheaty" than just extending the standard UI usability by modifying original options file.

edit: actually more OnTopic, Slingshot around should work, but due to its small gravity you would probably lose more speed correcting your ship for proper flyby than you gain from slingshot. Also for reference best case scenario slingshot from Mun can net you 400+m/s. Ike would probably give less than 50m/s

Edited November 3, 2013 by Nao

[SRV Ron]

Ike can give you big changes if you can catch it at the right spot at the right time.

[Nao]

@SRV Ron, Yes but the bigger the speed, the harder is for the moon/planet to alter your trajectory, and the amount of dV gained from slingshot is proportional to the trajectory change angle.

That's why you can get 400m/s+ slingshot from Mun when going to Eve (going to Eve actually cost's almost the same as just going to Mun that way). But when trying to get Mun slingshot to Jool it is 100 m/s gain at best.

edit: Did a simple ingame test, it takes around 600m/s dV to get from low Duna orbit to Kerbin, and at that speed Ike slingshot will give around 60-70m/s, 10% savings, not bad.

Edited November 4, 2013 by Nao

[Umlüx]

i did it!

used Ike to give me a small boost and instantly hit Kerbin SOI with my last drop of fuel. then i used RCS to alter the trajectory enough to get me deep inside Kerbins atmosphere and decoupled/landed the command/hab section safely on the ground.

@ Nao: 600m/s? what..? how..? i played around with maneuver nodes for half an hour and didnt get one burn below 1k d/v

seems, i do something wrong... or KAC shows me the wrong numbers for the transfer windows....

[Kasuha]

i did it!

used Ike to give me a small boost and instantly hit Kerbin SOI with my last drop of fuel. then i used RCS to alter the trajectory enough to get me deep inside Kerbins atmosphere and decoupled/landed the command/hab section safely on the ground.

Good job, congratulations!

[Nao]

i did it!

used Ike to give me a small boost and instantly hit Kerbin SOI with my last drop of fuel. then i used RCS to alter the trajectory enough to get me deep inside Kerbins atmosphere and decoupled/landed the command/hab section safely on the ground.

@ Nao: 600m/s? what..? how..? i played around with maneuver nodes for half an hour and didnt get one burn below 1k d/v

seems, i do something wrong... or KAC shows me the wrong numbers for the transfer windows....

Congratulations!

Since the Duna orbit is elliptic, during earlier testing i could get transfer Pe below Kerbin orbit with lower deltaV of around 540m/s. When trying actually to get a real transfer window in my testing save, it ended up little more: 610m/s from 50km orbit.

It is important that when exiting Duna SOI your trajectory should be as parallel to Kerbol orbit as possible. Ideally you should be at transfer orbit Ap right as you exit Duna SOI. And that's probably what costs you more dV than needed.

[Umlüx]

nice. damn.. now i have to try and redo this

thanks!