How to do a proper burn?

[Stealth2668]

I find that when near the end of the burn, the blue target (which you face when using nodes) quickly moves around the nav ball and I end up raising my Ap since I can't possibly follow it that fast (when circularizing for example). So when I cut my engines at an Ap of 100km then try and circularize using nodes, I manage to get my Pe to 100 km but by then my Ap is 200km... I'm sure I'm lining up perfectly in the beginning but then end always gets messed up and I end with a non circular orbit. I also tried starting early; I start maybe 5 secs early and I've tried doing half-and-half and still can't get a near circular orbit

[Specialist290]

From personal experience: If you're within ~5% of your target delta-v change for the node, you'll be just fine. You don't have to actually change your heading as the target moves; just kill your throttle before the delta-v meter starts going up again. The maneuver node system assumes an instantaneous change in velocity, so your actual burn is almost never going to be a perfect match to the plotted course (unless you use an autopilot to help).

It used to trip me up quite a bit, too, since I have a slight OCD tendency towards getting things exactly right.

[rflrob]

When doing circularization maneuvers, I like to stay in the map view (with the nav ball brought up so you can actually perform the maneuvers), then just watch the AP and PE nodes until they're in the right place. If you do your burns as close to AP as possible, then only your PE should be increasing, but in practice what I do is start my maneuvers a few seconds early, then keep the "Time until AP" readout around 5-10 seconds. When you're almost exactly circular, this becomes a lot harder, but I figure a circular orbit ±300m (which I can pretty routinely achieve) is close enough to circular as not to matter.

[dagothar]

I usually start maneuvers at half time of calculated burn before the node (ie. if burn is supposed to take 1 minute, I start at 30s before the node), unless dv is small - then I don't use full thrust and start at ~-5s, or use RCS. It all also depends on what situation are you in, as sometimes there is a plenty of time for corrections, and sometimes there isn't.

[Rune]

Yup, you don't lose anything by not being in a perfect circular orbit, and fiddling around with it can cost you. If you can learn to live with a bit of clutter, straight 50/50 on the burn will be pretty accurate on burns lasting less than 10 minutes. It's easy to plan correction maneuvers later anyhow, and the reason that is the way that is done in real life. It's mighty difficult to get an accuracy of 0.1 m/s on a 1km/s burn. But it's easier on a later 15m/s second maneuver.

Rune. Outside a gravity well, kick back and relax, you have time and can always correct. Think everything twice, act only when sure.

[Vanamonde]

The marker is calculating a mathematically precise heading on the fly, adjusting for every little wobble, and there's probably a bit of floating point slop in there, too. You'll drive yourself crazy trying to follow it exactly. I generally don't change my heading at all, once I've started a burn, knowing that the original heading will get me pretty darned close.

[georgTF]

You can allways reduce engine thrust once you're almost done with the burn. Do the last 10-20 m/s with minimal thrust if you have a powerfull engine. It will take a few extra seconds, but you will still nail it. Getting the correct amount of delta v is all that matters. At worst you will waste a little fuel, but with minimal thrust that's not really going to be an issue.

[steffen_anywhere]

Yeah... that happens when you overshoot with your manoeuvre burn. The easiest is actually to decrease engine power the closer you get to the end of the burn, then cut the engine with maybe 20 m/s to go and use RCS (if you're not short on RCS fuel). This is not a very efficient way, due to the use of RCS, but this way you will get the closest to the planned trajectory.