subroutine sbfout
output routine for satellite-probe numerical integration
paul macneil  nov.  1977
modification of:
becker/ash   oct. 1968   subroutine sbout
includes iteration with kalman filter (pm, nov., 1977)
nordsieck vtp output oddities corrected pm,dec.,1977

third end point written out, first point of next span
(if any) ready to be written during next entry, write
header/trailer
find new (next) times