input quantities
cond(1) = distance from central body
cond(2) = right ascension of position (reference epoch)
(between 0 and 360 deg)
cond(3) = declination of body (reference epoch)
(between -90 and 90 deg)
cond(4) = magnitude of velocity minus velocity in
circular orbit of radius cond(1)
cond(5) = azimuth of velocity vector on plane normal to
radius vector (between 0 and 360 deg)
cond(6) = flight path angle measured from radius vector to
velocity vector (between 0 and 180 deg)
goose   = sqrt(gm)
kind    = 0 if only coordinates needed, 1 if also partials
output quantities
x0(1-6) = cartesian components of position and velocity
referred to the mean equinox and equator of ref.epoch
dx0(i,j)= partial derivative of x0(i) with respect to cond(j)