Fig. 1

Model of Tiangong-1 and its body-fixed coordinate system. The main body of Tiangong-1 is 10.4 m in length with a maximum diameter of 3.35 m and a weight of 8.5 t. The two solar panels on either side of the satellite have dimensions of 7 m \(\times\) 3 m. A body-fixed coordinate system is established with the center of mass of the model as the origin O. The three coordinate axes are along the principal axes of inertia, where the Ox-axis points along the minimum axis of inertia in the docking direction and the Oz-axis follows the maximum axis of inertia. The principal moments of inertia are \(I_x = 16{,}403.01\,{{\rm kg\,m}}^2\), \(I_y = 70{,}915.56\,{{\rm kg\,m}}^2\), and \(I_z = 76{,}392.38\,{{\rm kg\,m}}^2\). The relative vector of the centers of the two corner cube reflectors on the docking interface (from the large one to the small one) can be expressed in the body-fixed coordinate system as \({\varvec{P}}_0 = (-0.2029, 0.6406, 2.6625)\,\hbox {m}\)