The Microwaves and Radar Institute of German Aerospace Center (DLR) is currently developing an experimental radar system called IoSiS (Imaging of Satellites in Space), for the purpose of gathering high-resolution radar images of objects in a low earth orbit. The basic purpose of the instrument is the analysis of satellite structures for detection of possible mechanical damages or irregularities generated by space debris, for example. Furthermore investigations on unknown objects or satellites can be performed. Based on inverse synthetic aperture radar (ISAR) geometry, the ground-based pulse radar creates high-resolution range profiles over a certain azimuth angle by tracking the space object or satellite using a steerable antenna system. The guided tracking of objects during overpass, whose trajectory is sufficiently known, allows wide azimuth observation angles. Thus high azimuth resolution in the order of the range resolution can be achieved. The range resolution is given by the radar bandwidth of up to 4.4 GHz resulting in a theoretical range resolution of up to few centimeters. Considering very high-resolution imaging of objects in a low earth orbit, several error sources have to be taken into account in order to achieve desired image quality. This paper outlines main challenges of the imaging process and discusses main error sources and its influence on the ISAR image. Such error sources, like atmospheric distortion or inaccurate orbit information, primarily generate severe blurring of the ISAR image making proper focusing very challenging. Therefore, proper error correction is essential.