subscp computes the latitude and longitude of the
sub-spacecraft point and the height of the spacecraft.
the longitude is put in dstf(2), the lat in dstf(3) and
the height in savb(48,1)
-180.lt.longitude.le.180 (measured east),
-90.le.latitude.le.90
height from center of planet in kilometers
this subroutine is turned on by ict(55)=1