Gravibreaking?

[Itchono]

Is it possible to get captured around Jool from a Kerbin-Jool interplanetary trajectory using Tylo or laythe? I just wanted try something other than aerocapture.

Edited September 1, 2013 by Itchono

[Motokid600]

Someone correct me if I'm wrong, but I'd say no. If you don't hit atmosphere or make a burn your speeds only going to increase from the slingshots

[Itchono]

I thought you could use a reverse slingshot to decrease your velocity but I don't know if it's enough.

[Motokid600]

No I'm pretty sure if you enter an SoI and don't make any maneuvers you will exit at a greater velocity. A different trajectory, but a faster speed. Why not just hit Laythe or Jool for an Areobrake? Saves a load of DV.

[iornfence]

It is absolutely possible to "Gravity brake". You aren't losing your momentum exactly, but ejecting retrograde to your target, in this case Jool. If you pass in front of the moon then leave it's gravity pointing retrograde to Jool, you should enter a stable orbit.

[UmbralRaptor]

It's doable, at least in theory. Just make sure you enter the moon's SOI on the leading side and exit on the trailing side.

[Awaras]

Yes, you can use a reverse slingshot around one of the moons to get captured into jool orbit. It all depends on the speed you enter Jool SOI, though. If you set up your hohmann transfer right you don't need to shed a lot of velocity to get captured. If you enter Jool SOI going at greater speed, you might have trouble getting a capture this way...

[Tex_NL]

I am actually surprised this subject comes up again. It does get asked at least once every few weeks.

Yes, you can brake using gravity assists and aerobraking. But it will NOT result in a stable orbit. You might slow down enough to stay within Jool's SoI but you will eventually re-encounter the body you last visited. It might happen in just a few orbits, it might take several years but you will encounter that body again. And anything can happen at that time. You might get slowed down, get a boost or become a permanent resident. Unless of course you stabilize your orbit with your engines before that time.

[Itchono]

Ok, thanks for the help! I'll adjust my orbit once in jool SOI

[KerbMav]

After burning (literally) through Duna's atmosphere with a probe, not having enough fuel to make an orbit and flying to high in the atmosphere to slow down enough by aerobreaking, I had an encounter with its moon. The slingshot surprised me with a nice, high orbit around Duna afterwards.

Did I actually loose momentum? Was the probe only thrown into an altitude in Duna's SOI at a velocity that corresponded with a valid orbit? Is it calculated correctly? Or is it just a quirk of KSP's two body engine that looks like a realistic result?

[Jackissimus]

After burning (literally) through Duna's atmosphere with a probe, not having enough fuel to make an orbit and flying to high in the atmosphere to slow down enough by aerobreaking, I had an encounter with its moon. The slingshot surprised me with a nice, high orbit around Duna afterwards.

Did I actually loose momentum? Was the probe only thrown into an altitude in Duna's SOI at a velocity that corresponded with a valid orbit? Is it calculated correctly? Or is it just a quirk of KSP's two body engine that looks like a realistic result?

It's a realistic result, absolutely. You can speed up as well as slow down using a slingshot.

If you pass a planet on its trailing side, you speed yourself up (the planet drags you with it for a while) and slow the planet down a tiny bit (you draw the planet to you, thus slowing it down). Similarly, if you pass a planet on its leading side, you slow yourself down and speed the planet up a bit.

[KerbMav]

So: sling around a moon (if present), aerobrake (if atmosphere is present) and only burn if needed to get captured - cannot establish an orbit cheaper (before circulization) then?

[Awaras]

So: sling around a moon (if present), aerobrake (if atmosphere is present) and only burn if needed to get captured - cannot establish an orbit cheaper (before circulization) then?

You can combine the slingshot and capture burn - due to the oberth effect, you get more 'bang per buck' (dV per unit of fuel expended) the faster you move and the closer you are to a gravity well. So, generally, IF you have to burn to get captured, the most efficient time to burn would be at or near your periapsis.

[Jackissimus]

So: sling around a moon (if present), aerobrake (if atmosphere is present) and only burn if needed to get captured - cannot establish an orbit cheaper (before circulization) then?

You can get captured without burning - by a moon slingshot or aerobraking. You can also almost completely circularize your orbit by aerobraking - that's what the Mars orbiters did.

You can always use lithobraking, although it's hard to circularize ...

EDIT: Oh, I think I understood what you were asking. To answer: it's impossible to establish an orbit around a body with no atmosphere and no moon without burning. However if you use a standard Hohmann transfer the burns to get captured are usually very small. More info here: http://forum.kerbalspaceprogram.com/showthread.php/41515-Is-it-possible-to-have-Mun-capture-you-in-orbit-around-it

Edited September 4, 2013 by Jackissimus

[KerbMav]

EDIT: Oh, I think I understood what you were asking. To answer: it's impossible to establish an orbit around a body with no atmosphere and no moon without burning.

Hence the brackets ...

I was simply listing the options to slow down (in an ideal situation).

But on another matter - from the thread you linked:

You never leave the SOI with a greater/less speed than you entered it when the speed is measured relative to the body of interest which is the measurement that matters when considering capture.

So the moon used to sling shot around adds to a vessels velocity during approach an equivalent dV (it has to, because it gets faster until it reaches the Pe of the encounter) as he takes away again when departing - only that the vessel adds the vector of the moon to its own and thereby gains speed relative to any other body in the system?

[Jackissimus]

So the moon used to sling shot around adds to a vessels velocity during approach an equivalent dV (it has to, because it gets faster until it reaches the Pe of the encounter) as he takes away again when departing - only that the vessel adds the vector of the moon to its own and thereby gains speed relative to any other body in the system?

Yeah, basically yeah. Although I am not sure about the exact speed you gain, you certainly gain some speed in the direction of the vector.

OT: I really wish there was a better way to monitor replies to your posts on this forum. I only found out you replied to me now.