detector units to the station instrument panel its orientation was determined by the station orientation mainly in two modes: 3-axes stabilization and orbital. In the first case the instrument axis had fixed orientation in space while in the second case it slowly ($\sim 4^o/min$) scanned the sky by the station orbital motion. Thus the different parts of the sky including Galactic Centre and Anti-Centre regions were accessible for observations during this experiment.

The sky region observed during the experiment is shown in Fig. 2 in equatorial coordinates. Different shades of gray represent the exposure time throughout the entire experiment. When estimating the exposure time, we assumed the angle between the source direction and the PX-2 axis to be no larger than $30^o$. In addition, we exclude the “Mir” residence time in the regions of trapped radiation. As a condition for the source being not shadowed by the Earth, we considered the requirement of PX-2 orientation to the sky, i.e. the angle between the PX-2 axis and the nadir-zenith direction should be within the range $0^o-90^o$. The figure also shows the brightest X-ray sources, slow pulsars and the Galactic equator. The typical exposure time can be determined by using observing conditions 