  The first orbital solution for the spectroscopic pair in the multiple star
system sigma Scorpii, determined from measurements with the Sydney University
Stellar Interferometer (SUSI), is presented. The primary component is of beta
Cephei variable type and has been one of the most intensively studied examples
of its class. The orbital solution, when combined with radial velocity results
found in the literature, yields a distance of 174(+23,-18) pc, which is
consistent with, but more accurate than the Hipparcos value. For the primary
component we determine 18.4+/-5.4 M_sun, -4.12+/-0.34 mag and 12.7+/-1.8 R_sun
for the mass, absolute visual magnitude and radius respectively. A B1 dwarf
spectral type and luminosity class for the secondary is proposed from the mass
determination of 11.9+/-3.1 M_sun and the estimated system age of 10 Myr.
