KOS

lock maxaccel to ship:maxthrust/ship:mass.
lock gravaccel to constant():G*ship:body:mass/(ship:altitude+ship:body:radius)^2.

set targethgt to 500.
until 0 {
	set targaccel to -(ship:verticalspeed^2)/(2*targethgt-ship:altitude).
	if ship:altitude<targethgt {
		lock throttle to (targaccel+gravaccel)/maxaccel.
	} else {
		lock throttle to (targaccel-gravaccel)/maxaccel.
	}.
	wait 1.
}.