Here's a quick mod-free technique to come up with a pretty good estimate for deciding when to start a suicide burn.  Even if you don't use it as your primary go-to technique, you can still use it as a backup "sanity check" for the numbers you get out of some other mod, such as KER: Get yourself on a suborbital trajectory. Zoom way in on the map view, and carefully place a maneuver node right on the spot where your trajectory intersects the surface (i.e. your impact point). Gr