yv      array for interpolation y-vectors
note: most interpolators use only 1-5, but the moon
uses 1-7
body    coordinates from integration tape
ndim    dimension of 'body' - max. # of partials + 1
icall   indicates which is the calling routine
1 - emtrp,  2 - mntrp,  3 - pltrp,  4 - sbtrp,
5 - sctrp,  6 -(prtrp), 7 -(ertrp), 8 - sotrp,
9 - ertsnt, 10 - sotrp for mercury
index   dimensions of y to set up (usually 3)