  In the domain of Space Situational Awareness (SSA), the challenges pertaining
to orbit determination and catalog correlation are notably pronounced, partly
attributable to the escalating presence of non-cooperative satellites engaging
in unspecified maneuvers at irregular intervals. This study introduces an
initial orbit determination methodology reliant upon data obtained from a
single surveillance radar, such as the Spanish Space Surveillance and Tracking
Surveillance Radar (S3TSR). The need for fast algorithms within an operational
context is considered here as the main design driver. The result is a
least-squares fitting procedure that incorporates an analytically formulated
approximation of the dynamics under the J2 perturbation, valid for short-term
propagation. The algorithm makes use of all available observables, including
range-rate, which makes it distinct from other similar methods. The method is
compared in a battery of synthetic tests against a classical range and angles
fitting method (GTDS) to study the effect of the track length and density of
measurements on the full state estimation. The presented methodology is quite
versatile, and it is leveraged to improve the estimation quality by adding
information of the object's orbital plane obtained from predictions. The
resulting method has been named OPOD.
