Shakey Numbers

[Rocket Farmer]

Is it just me or does everybody get the shakey numbers issue when flying.

Basically when trying to do an intercept sometimes the perapsis numbers jump about wildly. This is even after I have turned off my SAS/ASAS, turned off the RCS and even time warped a little to stop all rotation. I get bouncing numbers. Sometimes they bounce so bad that you can't read any number under 100,000 which makes it difficult to plan burns and even determine if a burn is helping or not. Other times they stay perfectly still the entire time.

I even get this just going out to Minmas sometimes (in that case usually the 10,000 numbers and less aren't readable.

Is this a floating point issue, my own personal computer hating me or something else that is fixable?

[sickboy]

happens to me a little bit, but definitely not in the 10,000 range

[Brapness]

happens to me often with larger ships, though it seems to reduce the closer I get to my destination. Usually it means I can't 'plan' burns, which has taught me instead to eyeball it and fly manually. If anyone does have a fix for this it would be nice.

[James_Eh]

I typed all of the below first, then carefully reread your question and don't think any of this will be of any help at all. Can't see how it could be a floating pt error, would suspect it stems from other mods or conflicts unless it is a straight KSP issue as below... Sorry, this is not too helpful and I would delete it except that there is a 1% chance is is not unhelpful...

The only time I have seen this is when:

1) peri and apo are so close to each other that they flip-flop repeatedly (who cares!?! circle!)

2) using MechJeb to predict aerobrake results from very far away

3) gently nudging peri/incl from very far away

I have never seen this inside Kerbin SOI. With one exception: when you have a "grazing" encounter with Mun on your way out to somewhere else, the ship path will bounce back and forth between "encounter" and "no encounter" and the resultant orbits will bounce accordingly. (Also happens when you leave the SOI of any planet/moon but with JUST enought delta-V to escape - you keep getting recaptured and escaping.) Usually clears up as you move along. I always treat that as DANGER and do a random minor burn until the ghost encounter stops flickering on to the screen...

[Z-Man]

Basically when trying to do an intercept sometimes the perapsis numbers jump about wildly.

I assume that means you are still very far away from the target body, right? The problem there is mostly due to the apparent fact that for orbit prediction, KSP does not use the current position and velocity of the center of mass of your craft. It uses the data from the part that is controlling the ship. So while you rotate or your ship or if it suffers from internal oscillations, those values vary, leading to different predictions.

Only remedy: be content with planning only a rough intercept from far away, do correction burns as go get closer. Once you are in the target body's SOI, accuracy should suffice.

[katateochi]

I don't normally have shaky numbers when doing local (Mun, Minmus) transfers, but it can happen around Kerbin if your orbit is almost perfectly circular (which is why I never bother with getting perfectly circular orbits).

Its a real pain when attempting to get accurate interplanetary transfers. when I did a Curiosity remake mission I wanted to set the correct Pe for aerobraking at Duna while I was still around Kerbin and that was a real pain. The way I deal with it is use the M-nodes to get the ruff trajectory, then once the main burn is complete I turn the m-node off and use the information feedback from the protractor mod while making fine adjustments with RCS.

[KvickFlygarn87]

That's because game engines aren't perfectly accurate, since the player doesn't care if the grenade he threw has an ever so slightly different bounce every time.

[sporkafife]

I know it's a bit annoying to not be able to accurately see your nodes from far away, but it is probably just the way that KSP's game engine only very roughly estimates the orbit going forward until you time accelerate and lock it in to place.

I suppose I take the approach that even NASA have to do mid course corrections, and they've got much more powerful computers and accurate models than I do to plan maneuvers with

[Rocket Farmer]

Thank-you for all the replys.

1. To answer a couple of questions I play totally stock.

2. Recently when doing a Duna encounter when I was already out of kerbins SOI it was bouncing between around 390,000 and 480,000km periapsis around Duna. This is after absolutely all ship movement had been cancelled with a little time warp and my course goes deep into Duna's SOI (ie not grazing).

3. When I time warp the number actually stops bouncing but starts as soon as I stop.

4. Even mid course corrections are jittery and tough. Basically I usually have to wait till 80-90% of the way there and as somebody above said eyeball it before then.

5. It only happens sometimes. Recently went to Eeloo without a single digit shake.

[Aragosnat]

Yeah. I have had it bounce around. Looks like it is most likely be a floating point problem. Where the end value is just right inbetween the tic and the toc. I do agree it does not happen often. But, it seems to happen more often at the edge of a SOI where it sems to have trouble knowing if you are in a SOI or not.

Or it could be showing what your periapsis is after encountering the SOI. Looking at the Duna where it has Ike. It could be also calculating the after or before effect of an Ike encounter too. As The game does try to calculate your path before and after hitting the SOI.