Knowledge of the maneuver axis of actively controlled satellites and the rotation axes of uncontrolled satellites is critical for maintaining Space Situational Awareness (SSA) and predicting satellite motions. Estimates of the spin rate and spin-axis of rotating satellites have been shown to be retrievable via passively collected time series of satellite brightness, otherwise known as light curves. Retrieval of satellite spin state parameters from light curves is accomplished by application of a physically derived relationship, the “Epoch Method," that explains the difference between the apparent spin rate and the inertial spin rate using the known relative motion between the observation telescope, the satellite, and the sun. There are two major challenges for retrieving the inertial spin rate from relative spin rate measurements operationally via the Epoch Method. One challenge is that satellites can have complex rotation states in the sense that they rotate about multiple axes with varying angular velocities. A second challenge is that the apparent difference between the inertial and relative spin rate is a direct function of the observer-to-solar geometry, meaning that geographical sites must be tasked optimally in order to maximize their ability to collect useful measurements for spin state retrieval. In order to overcome these challenges we derive an information metric that can both (1) explain the rotation axis that was maximally observable for a collected light curve from a geographic site, and (2) be utilized to task a diverse network of geographic sites for collecting maximally useful light curve measurements for monitoring the spin axis of an uncontrolled satellite. This is accomplished by deriving the observability of the inertial spin axis information according to the Fisher Information Matrix (FIM). We assume that the state vector that is being tracked is the inertial spin axis and that the measurement is an apparent spin rate measurement. We then derive a sensitivity matrix that utilizes the physical theory of the Epoch Method in deriving the partial derivatives of the measurement with respect to the state vector. We present several examples of how this metric can be applied towards tasking satellite networks across the continental United States for monitoring the inertial spin axis of Low Earth Orbit (LEO) and Geostationary (GEO) satellites.
Observability of Inertial Rotation Axis from Light Curve Derived Relative Spin Rate Measurements
J Astronaut Sci
01.10.2024
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
Light curve , Spin stability , Satellite , Fisher Information , Epoch Method , Space Situational Awareness Engineering , Aerospace Technology and Astronautics , Mathematical Applications in the Physical Sciences , Space Sciences (including Extraterrestrial Physics, Space Exploration and Astronautics)
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