On the Determination of Ajisai’s Spin Parameters from Graz Khz-slr Data

We determine the spin rate and spin direction of the spherical satellite AJISAI as well as its slow down between 2003/10 and 2005/06 using Graz full rate kHz satellite laser ranging (SLR) data. Since October 2003, the SLR station Graz/Lustbuehel as the first and only station worldwide is capable of laser ranging to Earth orbiting satellites with a laser pulse repetition rate of 2 kHz. The high density of the kHz observations compared to the regular 10 Hz systems results in a very precise scanning of the distribution and orientation of the satellite’s retroreflector panels during its spinning motion. The frequencies resulting from spectral analysis methods allow to identify the arrangement of the involved laser retro reflector panels at any instant in time. Using this method, we calculated the spin rate with very high accuracy (RMS of 4.6 × 10 Hz), and determined a slow down of the spin rate of 0.0081 Hz/yr during the investigated period. The main reason of this long term slow down is due to the interaction between the satellite’s metallic parts and the Earth’s magnetic field causing eddy currents. However, these mechanisms have not yet been modeled precisely. Furthermore, an approach was made to determine the attitude of AJISAI’s spin axis at any instant in time.