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RocketPropelledGiraffe

Multiple Encounters with the Same Body

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It seems The trajectory prediction for multiple encounters is confusing. This is sort of in between gameplay and technical question.

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If I do a swing-by on a body, leave its SOI, and get on a trajectory that immediately gets another encounter with the same body, the orbit prediction does not recognize the second encounter until the ship leaves the SOI.

Is this a limitation in the course plotting system, or basically just a corner case that almost never happens anyway and no one cares about it? I actually never noticed this until yesterday.

Edited by RocketPropelledGiraffe
image troubles.

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Looks like you only copied part of the link. The thing you want is the whole BBCode link.

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Thanks Vanamonde, I acually misclicked "start thread" instead of preview, messed up the link, and things sort of got downhill from there... ;)

I think I got it working now.

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I've had some similar weirdness with the trajectory plotting, but it's been in the Kerbin system. In my case it hasn't been the second encounter that doesn't display, but the first one.

Specifically, there have been multiple times where I set up a Minmus encounter that also happens to encounter the Mun on the way back. After I have it set up and warp a little bit, the Minmus encounter disappears, leaving me with just the Mun encounter shown. If I'm careful and cross Minmus' SOI at warp below the highest two levels I enter the SOI as expected, and the shown trajectory is now correct. If I use those top two levels of warp I pass through the SOI without it registering as such, and continue on the previous trajectory that leads to a Mun encounter.

This may be related or it may not, but there definitely seems to be some weirdness when the trajectory has multiple encounters.

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If I do a swing-by on a body, leave its SOI, and get on a trajectory that immediately gets another encounter with the same body, the orbit prediction does not recognize the second encounter until the ship leaves the SOI.

Is this a limitation in the course plotting system, or basically just a corner case that almost never happens anyway and no one cares about it? I actually never noticed this until yesterday.

Ah, the perils of navigating between Jool's moons :). The close proximity of so many relatively massive bodies with overlapping SOIs makes all sorts of weirdness happen out there. Granted, the whole patched conics system has difficulties with SOI changes in general, but the Joolian system just drives it nuts.

A good example is trying to do the most economical transfer from Laythe to Vall, whereby you leave Laythe nearly tangent to its orbit to meet Vall 1/2 an orbit later. If you do this, it will all look OK during your burn but it will almost certainly fall apart just after you leave Laythe's SOI. At that point, you're in Jool's SOI and the effects of Laythe are ignored in the 2-body gravity system. So, you're now in a slightly wider orbit than Laythe, which from Jool's POV means you should be going slower than Laythe, so that's what happens, and Laythe starts catching up from behind despite you having just burned a pile of fuel to be going faster. And because you took the efficient route, you're not diverging quickly from Laythe's path, so are still within reach of Laythe's wide SOI when it catches up with you. The patched conics, however, show your path continuing on towards Vall with no Laythe encounter, so you crank the warp up high to get the trip over quickly. Then suddenly, POOF, you're back in Laythe's SOI on a collision course with its center of mass, and will probably crash before you can react due to the warp speed :D. To avoid this, you have to do a less-efficient transfer to leave Laythe's orbit at a steeper angle, so that when Laythe catches up you're out beyond the reach of its SOI. Also, don't warp more than 100x until you see Laythe pass you by and know you're safe :).

Remember, the Kraken lives on Bop so things are going to be unpredictable in Jool's vicinity. Save early, save often, and never trust what your instruments are saying.

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Yeah, that happens sometimes.

If you want to fix it, put a maneuver node down on the orbit after the encounter. This will force the game to compute the next orbit and should show you the second encounter.

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