Determination of the rotation parameters of the AJISAI passive satellite using linear detection photometry and kHz SLR

The attitude motion of geodetic satellites can indirectly affect their orbit through non-gravitational perturbations. This effect is particularly significant for non-symmetrical bodies, as their orientation determines the surface areas subjected to atmospheric drag and radiative forces. However, this also applies, to a lesser extent, to fully spherical satellites due to thermal effects such as the Yarkovsky effect (Bertotti and Iess, 1991; Farinella et al., 1996; Métris et al., 1999; Andrés et al., 2004). Modelling the Yarkovsky effect requires, in particular, knowledge of the spin axis direction.

Due to the peculiar configuration of Ajisai mirrors, the photometry of flashes generated by the reflection of sunlight on their surfaces, and specifically the linear measurement of its luminous flux, appears to be the most adequate technique to study its rotation with high single-pass accuracy. Measurements of the Ajisai's luminous flux has been acquired using a high frequency (10 kHz) linear-detection optical photometry technique from the MéO telescope at Grasse station on the Plateau de Calern site of Observatoire de la Côte d'Azur. In this presentation we show that this instrumentation produces very rich informations. 

The selection, extraction, time-stamping and collection of the sequence of single flashes from the raw measured flux and the subsequent identification of the mirror on which the reflection occurred, allowed us to determine the rotation parameters of the satellite, i.e. to reconstruct its attitude, with an unprecedented single pass accuracy. The estimated precision for the determination of the rotation parameters during one pass of Ajisai is typically in the order of 0.25 deg for the spin axis orientation, 10^-5 s for the rotation period.

The growing number of kHz-capable Satellite Laser Ranging Stations and the extensive dataset made available by the International Laser Ranging Network (ILRS) position kHz SLR as a compelling tool with great potential for conducting medium- and long-term studies on the rotation of the Ajisai satellite.

Through the analysis of high repetition rate laser ranging data from the ILRS network, we were able to further investigate the rotation and confirm the photometry results. Similar to photometry, the sequence of CCRs closest approaches during the satellite pass observation could be identified and used to reconstruct the satellite's attitude.

A notable application of this work could be in the context of the next generation bistatic optical time transfer through a fully passive satellite.