r.reasenberg january 1972   subroutine sbeng
t. forni march 1976 fixed and added mariner6&7
spacecraft name used in &nmlst2 and sbeng must be identical
spacecraft engineering data inputed in this routine
returns sbmass, sbarea, ssav, sdel

table look up format
n.s/c-id-string is the number of elements in the
area and mass vectors.  it is one less than the number of
elements in the time vector.