Hypertemporal photometric measurement of spaceborne mirrors specular reflectivity for Laser Time Transfer link model

Abstract

The hypertemporal light curves of the sunlit Ajisai satellite allow for reflectivity measurement of the individual on-board mirror panels. The photon counting technology developed at Graz Satellite Laser Ranging (SLR) station makes it possible to distinguish between the solar flux diffused and specularly reflected off the spinning Ajisai. The flux intensities measured at 10 kHz sampling rate during the period from Oct. 2015 until Jan. 2018 are analyzed through the spacecraft micro-model link budget equation and indicate reflectivity of the 149 mirrors of between 82.3% and 88.2% with the mean value of 85.3% and the RMS of 1.2%. It is predicted that this high specular reflectivity of the satellite will allow for the establishment of a laser link between the distant ground locations with the individual mirrors acting as a zero-latency, passive optical relay. Simulations of the laser link between the Matera (Italy) and Graz (Austria) SLR systems via spaceborne mirror reflections indicate that such a channel can be operated at mean signal strength of 3.46 photoelectrons per laser pulse. The predicted mean number of the laser link intervals per pass is 874.6 with a mean interval duration of 9.15 ms.