  The Tisserand graph (TG) is a graphical tool commonly employed in the
preliminary design of gravity-assisted trajectories. The TG is a
two-dimensional map showing essential orbital information regarding the
Keplerian orbits resulting from the close passage by one or more massive
bodies, given the magnitude of the hyperbolic excess speed ($v_{\infty}$) and
the minimum allowed pericenter height for each passage. Contours of constant
$v_{\infty}$ populate the TG. Intersections between contours allow to link
consecutive flybys and build sequences of encounters en route to a selected
destination. When the number of perturbing bodies is large and many
$v_{\infty}$ levels are considered, the identification of all the possible
sequences of encounters through the visual inspection of the TG becomes a
laborious task. Besides, if the sequences are used as input for a numerical
code for trajectory design and optimization, an automated examination of the TG
is desirable. This contribution describes an automatic technique to explore the
TG and find all the encounter paths. The technique is based on a tree search
method, and the intersections between contours are found using the regula-falsi
scheme. The method is validated through comparisons with solutions available in
the open literature. Examples are given of application to interplanetary
mission scenarios, including the coupling with a trajectory optimizer.
