The scientific objectives of a space mission result into instrumental developments and specific satellite operations
to observe astronomical objects of interest. The payload in its space environment is however subject to important
thermal variations that affect observations. This is well observed when images of the Sun are recorded with the
constraint of keeping the solar rotational axis in a constant direction relatively to the camera reference frame.
Consequences are clearly observed on image positions that follow the thermal variations induced by the satellite
orbit. This is, in particular, the case for the space mission PICARD. This phenomenon is similar to defocus
and motions of images recorded with ground-based telescopes. We first present some simulations showing these
effects. We then compare our results with real data obtained from the space mission PICARD.