tomf Posted May 24, 2023 Share Posted May 24, 2023 (edited) During a large burn the position of the maneuvre node on the navball shifts around meaning that burns that significantly change the direction of the craft aren't executed as expected. Impact Large accurate burns are impossible. Reproduction This affects every maneuver to some extent but can be very clearly with the following reproduction Place a craft with a high TWR into a 100 km equatorial circular orbit of kerbin. (I used a mod to get my test craft into orbit) Create a maneuver node to plane shift the craft into a polar orbit. This should have a deta-v total of about 3181 (again using a mod I can see -2246 prograge, +2246 normal and +126 radial) Observe that the predicted orbit is now a polar orbit with 90 degree inclination and ~ 100km AP and PE Use SAS to orient the craft Try to execute the maneuvre Observe that the burn progress bar decreases to about half way then starts going up again. Continue the burn for the predicted length of time (in my case this burn was predicted to take 29 seconds Observe that you are now completely the wrong trajectory Analysis The issue appears to be that as the burn was executed the maneuvre node moved in order to stay fixed relative to the current velocity of the craft. However the projected trajectory line (and the KSP 1 behaviour) shows the result of the burn at a fixed direction relative to the body being orbited. For this maneuvre I would expect the burn to be fixed at a 45 degrees north while the velocity markers will migrate from initially having prograde at 90 degrees moving upwards to 0 degrees at then end with prograde passing under the maneuvre marker half way through the burn. Workaround (untested) Use SAS to allign with the node and then switch to SAS locked heading mode and ignore the maneuvre node wandering. Edited June 1, 2023 by Anth12 adding version Link to comment Share on other sites More sharing options...
tomf Posted May 24, 2023 Author Share Posted May 24, 2023 Just to add - this could be a useful advanced feature for very low TWR burns where the craft needs to spiral out with a single burn lasting a significant fraction of the orbit, but the maneuvre node predicted orbit needs to support it and definitely shouldn't be a default. Link to comment Share on other sites More sharing options...
Sea_Kerman Posted June 1, 2023 Share Posted June 1, 2023 (edited) Can confirm that having SAS on “attitude hold” mode instead of “point at maneuver” mode is a functional workaround. The maneuver aimpoint does indeed seem to rotate and maintain angle relative to your current velocity instead of your initial orbit. Edited June 1, 2023 by Sea_Kerman Link to comment Share on other sites More sharing options...
Spicat Posted June 1, 2023 Share Posted June 1, 2023 Can confirm, same bug I reported some time ago (which seems to be the case for only normal and anti-normal): Link to comment Share on other sites More sharing options...
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