Time To Impact

// cos true anomaly (cos(v))        cos(v) =  (((SMA(1-e^2))/r) - 1) / e

    local   geoimpact       IS  ADDONS:TR:IMPACTPOS.
    local   SMAA            IS  SHIP:ORBIT:SEMIMAJORAXIS.
    local   SMAB            IS  (SQRT((PERIAPSIS + SHIP:BODY:RADIUS) * (APOAPSIS + SHIP:BODY:RADIUS))).
    local   Ecce            IS  SQRT(1 - ((SMAB^2)/(SMAA^2))).
    local   radiusimp       IS  (SHIP:BODY:RADIUS + geoimpact:TERRAINHEIGHT).
    local   radiuscur       IS  (SHIP:ALTITUDE + SHIP:BODY:RADIUS).
    local   cosvimp         IS  ((((SMAA * (1 - ecce^2)) / radiusimp) - 1) / ecce).
    local   cosvcur         IS  ((((SMAA * (1 - ecce^2)) / radiuscur) - 1) / ecce).

// eccentric anomaly (E)            E = ArcCos [ (e + cos(v)) / (1 + e * cos(v)) ]

    local   EcceAnomImp     IS  ARCCOS((ecce + cosvimp) / (1 + ecce * cosvimp)).
    local   EcceAnomCur     IS  ARCCOS((ecce + cosvcur) / (1 + ecce * cosvcur)).

// Mean anomaly (M)                 M = E - e * sin(E)

    LOCAL MeanAnomImp           IS ecceAnomImp - (ecce * SIN(ecceAnomImp)).
    LOCAL MeanAnomCur           IS ecceAnomCur - (ecce * SIN(ecceAnomCur)).

// Mean notion anomaly (n)          n = 360 / P

    local   gravmu          IS  (SHIP:BODY:MASS * CONSTANT:G).
    local   orbperiod       IS  (2 * constant:pi * SQRT((SMAA^3)/(GravMu))).
    local   meanmotion      IS  (360 / orbperiod).

// Time calc

    local   deltatime       IS  (MeanAnomCur - MeanAnomImp)/Meanmotion.

    print   "time to impact: " + ROUND(deltatime) + " seconds.".