When to Start Burns

[Lar-E]

Per the wiki "For best results the burn should be initiated roughly half of the duration of the burn before the indicated burn time." This has been working pretty well for me. My question is, does this rule of thumb hold true for longer burns, in the 4-6 minute range? And what is the rationale behind this?

[BigFatStupidHead]

The maneuver node system (and the math it is based on) expects all the force of the burn to be delivered instantaneously. Because this is a physical impossibility, we have to make as close an approximation as possible, and do that by burning half before, then half after.

[Specialist290]

For most burns, splitting the duration in half on either side of the burn works well enough, with a few minor corrections.

Of course, if you want to get the most efficiency out of your longer burns, what you really want to do is split the delta-v expended in half, not the time. This gets a little complicated to calculate exactly, but this tutorial has the equations you'll need, as well as a decent "back-of-envelope" method for estimating the ideal time to begin your burn.