x      = output coordinates of earth or earth-moon barycenter
relative to center of mass of solar system
determined from n-body tape by calling solcnt & ertsnt
output units are au and au/day
input quantities are
jd     = julian day number
fract  = coordinate time fraction of day
nvel   = 0 x(1-3) position output
nvel   = 1 x(4-6) velocity output
ntype  = 0 earth-moon barycenter relative to center of mass
of solar system
ntype  = 1 earth relative to center of mass of solar system