Measure periapsis from planet center instead of surface

The periapsis is reported as NA if its below the planet surface - this is wrong, because as property of the orbit it is perfectly well defined even if the orbit happens to intersect the surface. You should see e.g. the effect of a burn in raising the periapsis and then you can also see how far from a stable orbit you are. One way to do this is to report the periapsis as a distance from the planet center (e.g. printed red if its smaller than the planetradius), alternatively it could be reported as negative number.