Rotation analysis of unknown LEO objects from light curves using periodicity fluctuations and pattern recognition

Kurzfassung

Spatially unresolved light curves are a useful tool for the rotational analysis and characterization of orbital objects. While the light curve itself comprises only a time series of the one-dimensional data on signal brightness, positional data of the observation geometry, which quickly changes during the light curve measurement, can be exploited to deduce possible directions of the object’s rotational axis.

Two sophisticated light curve inversion methods for target-agnostic rotation analysis are presented which can be used without any prior knowledge about the orbital object itself. Solely assuming that its rotational axis is fixed with respect to the geocentric inertial system, the epoch method (Hall et al., 2006) as well as the photometric patterns method (Koshkin et al., 2024) make use of periodic structures within the light curve signal. The epoch method utilizes small variations of the observed synodic period to derive the rotational axis, since those variations stem from a shift in the object-fixed longitude of the observation scene that reduces or increases the signal period, similar to the Doppler effect in translational motion.

In the photometric patterns method, the angle between phase-angle bisector and the rotation plane of the target is employed to attribute the object-fixed latitude of observation to identical light curve patterns from different observations, from which the direction of the rotation axis can be concluded.

Both methods are analyzed and validated by means of synthetic light curves from our raytracing-based simulation tool Raxus Prime. Benefits and drawbacks of each method are illustrated for exemplary targets. A perspective of usefulness and constraints of both methods for their practical application is outlined using high-resolution data from light curve observations of objects in the low Earth orbit.