  We have developed a new, fast method of estimating the orbital properties of
a binary or triple system using as few as two epochs of astrometric data. FOBOS
(Few Observation Binary Orbit Solver) uses a flat prior brute force Monte Carlo
method to produce probability density functions of the likely orbital
parameters. We test the code on fake observations and show that it can (fairly
often) constrain the semi-major axis to within a factor of 2-3, and the
inclination to within $\sim$20$^{\circ}$ from only two astrometric
observations. We also show that the 68 and 95 per cent confidence intervals are
statistically reliable. Applying this method to triple systems allows the
relative inclination of the secondary and tertiary star orbits to be
constrained. FOBOS can usually find a statistically significant number of
possible matches in CPU minutes for binary systems, and CPU hours for triple
systems.
