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Figure 2.8: The ROSAT spacecraft coordinate frame. This virtual right-handed frame is fixed to the spacecraft and the axis is aligned with the optical axis of the XRT in the pointing direction, while the axis is perpendicular to the solar panels in the anti-sun direction [Hasinger1990a].
The aspect solution for a given observation is referenced to the ROSAT (S/C) cartesian coordinate system ( ). This virtual right-handed frame is fixed to the S/C (Fig. 2.8) with the -axis aligned with the optical axis of the XRT (and parallel to that of the WFC) in the pointing direction, and the -axis perpendicular to the solar panels in the anti-Sun direction. In orbit, the ROSAT coordinate system is defined by the GSOC attitude solution derived from the measurement of stars in the star tracker FOV\ (Sect. 1.2.5).