Maneuver Node Plot/Burn Not Accurate

[Scarecrow71]

While playing yesterday and today, I noticed that some of my plotted maneuvers do not end up where they should after I burn.  As an example, here is the plotted course for a Mun landing, followed by the actual course after the burn.

The burn was to take 331 dV, which should leave me with 1829 dV.  And while I went over that amount slightly, the course is nowhere close to where I originally plotted it.  The landing point is well south (relatively speaking) of where I originally plotted it, which should not happen unless I redo the maneuver node and/or over/under burn.  And this wasn't a one-time thing; below you'll see shots of the plotted and actual courses for a return trip from the Mun.

This burn was to take 360 dV leaving me with 544.  I went over a bit - 5 m/s - but that should not have caused this ridiculous change in course.  I would have had to continue burning to even get close to what was plotted.

This is a bug.  A pretty serious one, as you cannot rely upon what you plot, which will in turn prevent players from going where they wish with any accuracy.  This is nearly game-breaking and needs attention.

[Hecatonichosachoron]

I had a similar issue.  I made an escape burn from Minmus, and the projected orbit after leaving minmus incorrectly showed a higher energy orbit escaping Kerbin altogether instead of the lower-energy orbit. 

Before exiting SOI:

After exiting SOI:

 

Edited February 26, 2023 by Hecatonichosachoron
reformatting image link

[Draradech]

There are multiple bugs with maneuver nodes. They appear to be accurate if you switch to SAS hold directly before the burn, and don't toggle map mode. Longer discussion in here: 

 

[Scarecrow71]

1 hour ago, Draradech said:

There are multiple bugs with maneuver nodes. They appear to be accurate if you switch to SAS hold directly before the burn, and don't toggle map mode. Longer discussion in here: 

 

If you take a look at the images I shared, I am holding on the node itself.

[Draradech]

4 minutes ago, Scarecrow71 said:

If you take a look at the images I shared, I am holding on the node itself.

Yes, that's the problem. The node direction as indicated on the navball, and followed by SAS, drifts away during the burn.
If you look at my images in here, it works with SAS hold (the padlock icon): 

 

[Scarecrow71]

13 minutes ago, Draradech said:

Yes, that's the problem. The node direction as indicated on the navball, and followed by SAS, drifts away during the burn.
If you look at my images in here, it works with SAS hold (the padlock icon): 

 

Hold the phone.  Holding the node no longer works?  Clicking on the node icon to gold the node no longer works?  That is a bug.  Why?  I don't have to click the lock icon to gold prograde or reteograde; why should I have to in order to hold the maneuver node (which is part of SAS)?

[Draradech]

18 minutes ago, Scarecrow71 said:

Hold the phone.  Holding the node no longer works?  Clicking on the node icon to gold the node no longer works?  That is a bug.  Why?  I don't have to click the lock icon to gold prograde or reteograde; why should I have to in order to hold the maneuver node (which is part of SAS)?

Actually, you do need to do that for prograde maneuvers as well. All maneuvers are assumed to have constant pointing. Your prograde changes during your burn, leading to inaccurate results if you turn with it. That's weird if coming from KSP1 (with half before half after burning - which is an approximation), but viewed without that frame of reference it makes sense (and is more accurate).
For the maneuver direction I agree it's a bug. If the maneuver is supposed to have constant pointing, the indicator and SAS shouldn't drift.

[skogs]

Confirm strange behavior.  The maneuver node that is the direction I'm supposed to burn...yeah it should not move around like the rest. Almost left orbit entirely instead of comfortably bouncing out to Minmus.

 

[Niko_Dragovich]

Same problem as Hecatonichosachoron for Minmus.

Edited February 27, 2023 by Niko_Dragovich

[Scarecrow71]

1 hour ago, Draradech said:

Actually, you do need to do that for prograde maneuvers as well. All maneuvers are assumed to have constant pointing. Your prograde changes during your burn, leading to inaccurate results if you turn with it. That's weird if coming from KSP1 (with half before half after burning - which is an approximation), but viewed without that frame of reference it makes sense (and is more accurate).
For the maneuver direction I agree it's a bug. If the maneuver is supposed to have constant pointing, the indicator and SAS shouldn't drift.

I think we are saying the same thing.  I have clicked on the node icon in the SAS tray and am holding the node.

[Draradech]

For now, you can work around by pointing at maneuver, clicking the padlock shortly before burn start, and burn as indicated by the timer. The result will be accurate. (Oh, and don't toggle map view - that resets the node...)

Edited February 27, 2023 by Draradech

[Scarecrow71]

47 minutes ago, Draradech said:

For now, you can work around by pointing at maneuver, clicking the padlock shortly before burn start, and burn as indicated by the timer. The result will be accurate. (Oh, and don't toggle map view - that resets the node...)

I shouldn't have to click the Lock icon; simply clicking the maneuver node icon should hold the maneuver node.  Both of these are bugs; neither should happen.  There was no lock in KSP1, and there is nothing in the game itself that I've seen that indicates this needs to happen.  I mean, what's the point of clicking the icon if you then have to click something else to make it stick?

[Draradech]

1 minute ago, Scarecrow71 said:

I shouldn't have to click the Lock icon; simply clicking the maneuver node icon should hold the maneuver node.  Both of these are bugs; neither should happen.  There was no lock in KSP1, and there is nothing in the game itself that I've seen that indicates this needs to happen.  I mean, what's the point of clicking the icon if you then have to click something else to make it stick?

I agree. That's why I said it is a work around. When the bug is fixed, you will no longer need to click the lock icon to keep pointing in the correct direction. The bug is that the indicated maneuver direction drifts during the burn. Switching to "hold orientation" (the lock) keeps you pointed in the intended direction for now (until they fix the problem).

[Scarecrow71]

3 hours ago, Draradech said:

I agree. That's why I said it is a work around. When the bug is fixed, you will no longer need to click the lock icon to keep pointing in the correct direction. The bug is that the indicated maneuver direction drifts during the burn. Switching to "hold orientation" (the lock) keeps you pointed in the intended direction for now (until they fix the problem).

So, I did a Mun landing this morning (practice makes perfect, and I'm not skilled at doing that manually having let MJ do it for me the last few years), and your help worked...partially.  With the transfer burn, I clicked to hold the maneuver, then turned off SAS, then turned it back on (both by clicking the Lock button), then clicked the maneuver node again.  This held the maneuver and the transfer burn worked fine.

The landing burn, however, did not.  I did the above stuff multiple times, and the burn still didn't not happen the way it was plotted.  I ended up having to do a manual burn, pointing to different things (a bit prograde, a bit radial, etc.) before I was able to get a landing site that was suitable enough/close enough to where I originally plotted it.

So yeah, the advice helps with interplanetary (or, in this case, planet-to-Mun) transfer burns, but not with landing.  Unless I missed something?

[Draradech]

Click the lock once before you start the burn. The label is wrong, it doesn't turn sas off, it switches to "hold direction". Do not follow "maneuver" pointing with sas during burn, the bug is that maneuever pointing drifts during the burn.

[Scarecrow71]

1 hour ago, Draradech said:

Click the lock once before you start the burn. The label is wrong, it doesn't turn sas off, it switches to "hold direction". Do not follow "maneuver" pointing with sas during burn, the bug is that maneuever pointing drifts during the burn.

No, mine either turns SAS on or turns it off, depending upon what it's at when I click it.  But, if you are saying to turn it off then turn it back on, and don't click on the node icon...I can try that next time to see what happens!

[Billy1996]

Same. Maneuver node doesn't work for me.  put SAS on maneuver point ,  did all steps correctly (start/stop burning  with green checks) but after that, my orbit doesn't matches manouvrer orbit , and my ship keep fallen to Kerbin. 
 

 

Edited February 27, 2023 by Billy1996

[Draradech]

1 hour ago, Scarecrow71 said:

No, mine either turns SAS on or turns it off, depending upon what it's at when I click it.  But, if you are saying to turn it off then turn it back on, and don't click on the node icon...I can try that next time to see what happens!

Turning SAS off is done by the button "SAS" closer to the navball. If SAS is off and you tap "a" (or any direction key for that matter) the craft will spin and won't stop by itself. Clicking the lock once sets SAS to hold its current direction. If you tap a key you turn a bit and then hold this new direction.

35 minutes ago, Billy1996 said:

Same. Maneuver node doesn't work for me.  put SAS on maneuver point ,  did all steps correctly (start/stop burning  with green checks) but after that, my orbit doesn't matches manouvrer orbit , and my ship keep fallen to Kerbin. 

Yes. SAS on maneuver doesn't work, because the maneuver indicator drifts during the burn (I consider this a bug, we'll see). As a workaround you can switch SAS to hold direction (click lock icon once) directly before the burn.

 

 

For reference:

 

[Scarecrow71]

4 minutes ago, Draradech said:

Turning SAS off is done by the button "SAS" closer to the navball. If SAS is off and you tap "a" (or any direction key for that matter) the craft will spin and won't stop by itself. Clicking the lock once sets SAS to hold its current direction. If you tap a key you turn a bit and then hold this new direction.

For reference:

 

That explains it perfectly.  Thank you for that!