kreflt=1 albedo radiation
=2 infared radiation
=3 both inrared and albedo
kradgo    =iabs(kkp(78) )
0         mariner-9 general-purpose 3-axis
seven-term model
1         rad georgevic model put in by
l.e. conrod and r.mckinnis    (1975)
2         mvm model of c christensen
3         viking model of c christensen
4         pvo - put in by r.b.g.  dec. 1978

ncall=-2 setup once per iteration of a given step for partials
ncall=-1 setup once per iteration of a given step for motion
ncall= 0 setup once per step
ncall= k evaluate acceleration for equation k.gt.0

sh = scale height (km)
rhoz= density at height h0 (gm/cm**3)
drgeps = upper limit on exponent in atmden
cdrg1 = drag coefficient
cdrg2 = drag coefficient
rhzkm = distance from center of planet to height h0

kp(81)= kreflt*10+ kdirct
kdirct=0 no radiation pressure
=1 direct radiation,exact shadow
=2 direct radiation,approx. shadow.(not coded)
=3 direct radiation, no shadow

*  start=1000
start of code that establishes rlim, the s/c height above
which drag is of no interest.
iset
0 initial
-1 drag was insignificant
1 drag was significant
2 drag has changed from insig. to sig. or vice-versa
idrag
-1 insignificant
0 significant

*  start=3500
effect of low-thrust forces on partial derivatives
the effect on position and velocity is not included
see if partial is w/r/t a probe con